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diff --git a/5765-h/5765-h.htm b/5765-h/5765-h.htm new file mode 100644 index 0000000..7870746 --- /dev/null +++ b/5765-h/5765-h.htm @@ -0,0 +1,18226 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" +"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> +<head> +<meta http-equiv="Content-Type" content="text/html;charset=utf-8" /> +<meta http-equiv="Content-Style-Type" content="text/css" /> +<title>The Project Gutenberg eBook of Insectivorous Plants, by Charles Darwin</title> + +<style type="text/css" xml:space="preserve"> + +body { margin-left: 20%; + margin-right: 20%; + text-align: justify; } + +h1, h2, h3, h4, h5 {text-align: center; font-style: normal; font-weight: +normal; line-height: 1.5; margin-top: .5em; margin-bottom: .5em;} + +h1 {font-size: 300%; + margin-top: 0.6em; + margin-bottom: 0.6em; + letter-spacing: 0.12em; + word-spacing: 0.2em; + text-indent: 0em;} +h2 {font-size: 150%; margin-top: 2em; margin-bottom: 1em;} +h3 {font-size: 130%; margin-top: 1em;} +h4 {font-size: 120%;} +h5 {font-size: 110%;} + +.no-break {page-break-before: avoid;} /* for epubs */ + +div.chapter {page-break-before: always; margin-top: 4em;} + +hr {width: 80%; margin-top: 2em; margin-bottom: 2em;} + +p {text-indent: 1em; + margin-top: 0.25em; + margin-bottom: 0.25em; } + +.p1 {margin-top: 1em;} + +p.letter {text-indent: 0%; + margin-left: 10%; + margin-right: 10%; + margin-top: 1em; + margin-bottom: 1em; } + +p.noindent {text-indent: 0% } + +p.center {text-align: center; + text-indent: 0em; + margin-top: 1em; + margin-bottom: 1em; } + +p.footnote {font-size: 90%; + text-indent: 0%; + margin-left: 10%; + margin-right: 10%; + margin-top: 1em; + margin-bottom: 1em; } + +sup { vertical-align: top; font-size: 0.6em; } + +a:link {color:blue; text-decoration:none} +a:visited {color:blue; text-decoration:none} +a:hover {color:red} + +</style> + </head> + <body> + +<div style='text-align:center; font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of Insectivorous Plants, by Charles Darwin</div> +<div style='display:block; margin:1em 0'> +This eBook is for the use of anyone anywhere in the United States and +most other parts of the world at no cost and with almost no restrictions +whatsoever. You may copy it, give it away or re-use it under the terms +of the Project Gutenberg License included with this eBook or online +at <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you +are not located in the United States, you will have to check the laws of the +country where you are located before using this eBook. +</div> +<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: Insectivorous Plants</div> +<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Author: Charles Darwin</div> +<div style='display:block; margin:1em 0'>Release Date: August 31, 2002 [eBook #5765]<br /> +[Most recently updated: December 28, 2021]</div> +<div style='display:block; margin:1em 0'>Language: English</div> +<div style='display:block; margin:1em 0'>Character set encoding: UTF-8</div> +<div style='display:block; margin-left:2em; text-indent:-2em'>Produced by: Sue Asscher and David Widger</div> +<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK INSECTIVOROUS PLANTS ***</div> + + +<h1>INSECTIVOROUS PLANTS</h1> + +<h2 class="no-break">By Charles Darwin</h2> + +<hr /> + +<h2>CONTENTS</h2> + +<table summary="" style=""> + +<tr> +<td> <a href="#link2H_4_0001">DETAILED TABLE OF CONTENTS.</a></td> +</tr> + +<tr> +<td> <a href="#link2H_4_0002">INSECTIVOROUS PLANTS.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0001">CHAPTER I. DROSERA ROTUNDIFOLIA, OR THE COMMON SUN-DEW.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0002">CHAPTER II. THE MOVEMENTS OF THE TENTACLES FROM THE CONTACT OF SOLID BODIES.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0003">CHAPTER III. AGGREGATION OF THE PROTOPLASM WITHIN THE CELLS OF THE TENTACLES.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0004">CHAPTER IV. THE EFFECTS OF HEAT ON THE LEAVES. </a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0005">CHAPTER V. THE EFFECTS OF NON-NITROGENOUS AND NITROGENOUS ORGANIC FLUIDS ON THE LEAVES.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0006">CHAPTER VI. THE DIGESTIVE POWER OF THE SECRETION OF DROSERA.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0007">CHAPTER VII. THE EFFECTS OF SALTS OF AMMONIA. </a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0008">CHAPTER VIII. THE EFFECTS OF VARIOUS OTHER SALTS AND ACIDS ON THE LEAVES.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0009">CHAPTER IX. THE EFFECTS OF CERTAIN ALKALOID POISONS, OTHER SUBSTANCES AND VAPOURS.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0010">CHAPTER X. ON THE SENSITIVENESS OF THE LEAVES, AND ON THE LINES OF TRANSMISSION OF THE MOTOR IMPULSE.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0011">CHAPTER XI. RECAPITULATION OF THE CHIEF OBSERVATIONS ON DROSERA ROTUNDIFOLIA.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0012">CHAPTER XII. ON THE STRUCTURE AND MOVEMENTS OF SOME OTHER SPECIES OF DROSERA.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0013">CHAPTER XIII. DIONAEA MUSCIPULA.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0014">CHAPTER XIV. ALDROVANDA VESICULOSA.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0015">CHAPTER XV. DROSOPHYLLUM—RORIDULA—BYBLIS—GLANDULAR HAIRS OF OTHER PLANTS—CONCLUDING REMARKS ON THE DROSERACEÆ.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0016">CHAPTER XVI. PINGUICULA.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0017">CHAPTER XVII. UTRICULARIA.</a></td> +</tr> + +<tr> +<td> <a href="#link2HCH0018">CHAPTER XVIII. UTRICULARIA (continued).</a></td> +</tr> + +<tr> +<td> <a href="#link2H_CONC">CONCLUSION.</a></td> +</tr> + +<tr> +<td> <a href="#link2H_4_0022">INDEX.</a></td> +</tr> + +</table> + +<hr /> + +<div class="chapter"> + +<h2><a name="link2H_4_0001" id="link2H_4_0001"></a> +DETAILED TABLE OF CONTENTS. +</h2> + +<p class="noindent"> +<a href="#link2HCH0001">CHAPTER I.</a><br/> +DROSERA ROTUNDIFOLIA, OR THE COMMON SUN-DEW.<br/> +Number of insects captured—Description of the leaves and their appendages +or tentacles— Preliminary sketch of the action of the various parts, and +of the manner in which insects are captured—Duration of the inflection of +the tentacles—Nature of the secretion—Manner in which insects are +carried to the centre of the leaf—Evidence that the glands have the power +of absorption—Small size of the roots.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0002">CHAPTER II.</a><br/> +THE MOVEMENTS OF THE TENTACLES FROM THE CONTACT OF SOLID BODIES.<br/> +Inflection of the exterior tentacles owing to the glands of the disc being +excited by repeated touches, or by objects left in contact with +them—Difference in the action of bodies yielding and not yielding soluble +nitrogenous matter—Inflection of the exterior tentacles directly caused +by objects left in contact with their glands—Periods of commencing +inflection and of subsequent re-expansion—Extreme minuteness of the +particles causing inflection—Action under water—Inflection of the +exterior tentacles when their glands are excited by repeated +touches—Falling drops of water do not cause inflection.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0003">CHAPTER III.</a><br/> +AGGREGATION OF THE PROTOPLASM WITHIN THE CELLS OF THE TENTACLES.<br/> +Nature of the contents of the cells before aggregation—Various causes +which excite aggregation—The process commences within the glands and +travels down the tentacles— Description of the aggregated masses and of +their spontaneous movements—Currents of protoplasm along the walls of the +cells—Action of carbonate of ammonia—The granules in the protoplasm +which flows along the walls coalesce with the central masses—Minuteness +of the quantity of carbonate of ammonia causing aggregation—Action of +other salts of ammonia—Of other substances, organic fluids, +&c.—Of water—Of heat—Redissolution of the aggregated +masses—Proximate causes of the aggregation of the +protoplasm—Summary and concluding remarks—Supplementary +observations on aggregation in the roots of plants.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0004">CHAPTER IV.</a><br/> +THE EFFECTS OF HEAT ON THE LEAVES.<br/> +Nature of the experiments—Effects of boiling water—Warm water +causes rapid inflection— Water at a higher temperature does not cause +immediate inflection, but does not kill the leaves, as shown by their +subsequent re-expansion and by the aggregation of the protoplasm— A still +higher temperature kills the leaves and coagulates the albuminous contents of +the glands.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0005">CHAPTER V.</a><br/> +THE EFFECTS OF NON-NITROGENOUS AND NITROGENOUS ORGANIC FLUIDS ON THE LEAVES.<br/> +Non-nitrogenous fluids—Solutions of gum +arabic—Sugar—Starch—Diluted alcohol—Olive oil— +Infusion and decoction of tea—Nitrogenous +fluids—Milk—Urine—Liquid albumen—Infusion of raw +meat—Impure mucus—Saliva—Solution of +isinglass—Difference in the action of these two sets of +fluids—Decoction of green peas—Decoction and infusion of +cabbage—Decoction of grass leaves.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0006">CHAPTER VI.</a><br/> +THE DIGESTIVE POWER OF THE SECRETION OF DROSERA.<br/> +The secretion rendered acid by the direct and indirect excitement of the +glands—Nature of the acid—Digestible substances—Albumen, its +digestion arrested by alkalies, recommences by the addition of an +acid—Meat—Fibrin—Syntonin—Areolar +tissue—Cartilage—Fibro-cartilage— Bone—Enamel and +dentine—Phosphate of lime—Fibrous basis of +bone—Gelatine—Chondrin— Milk, casein and +cheese—Gluten—Legumin—Pollen—Globulin—Haematin—Indigestible +substances—Epidermic productions—Fibro-elastic +tissue—Mucin—Pepsin—Urea—Chitine— +Cellulose—Gun-cotton—Chlorophyll—Fat and +oil—Starch—Action of the secretion on living seeds—Summary +and concluding remarks.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0007">CHAPTER VII.</a><br/> +THE EFFECTS OF SALTS OF AMMONIA.<br/> +Manner of performing the experiments—Action of distilled water in +comparison with the solutions—Carbonate of ammonia, absorbed by the +roots—The vapour absorbed by the glands—Drops on the +disc—Minute drops applied to separate glands—Leaves immersed in +weak solutions—Minuteness of the doses which induce aggregation of the +protoplasm—Nitrate of ammonia, analogous experiments with—Phosphate +of ammonia, analogous experiments with—Other salts of +ammonia—Summary and concluding remarks on the action of salts of +ammonia.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0008">CHAPTER VIII.</a><br/> +THE EFFECTS OF VARIOUS OTHER SALTS, AND ACIDS, ON THE LEAVES.<br/> +Salts of sodium, potassium, and other alkaline, earthy, and metallic +salts—Summary on the action of these salts—Various +acids—Summary on their action.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0009">CHAPTER IX.</a><br/> +THE EFFECTS OF CERTAIN ALKALOID POISONS, OTHER SUBSTANCES AND VAPOURS.<br/> +Strychnine, salts of—Quinine, sulphate of, does not soon arrest the +movement of the protoplasm—Other salts of +quinine—Digitaline—Nicotine—Atropine—Veratrine— +Colchicine— +Theine—Curare—Morphia—Hyoscyamus—Poison of the cobra, +apparently accelerates the movements of the protoplasm—Camphor, a +powerful stimulant, its vapour narcotic—Certain essential oils excite +movement—Glycerine—Water and certain solutions retard or prevent +the subsequent action of phosphate of ammonia—Alcohol innocuous, its +vapour narcotic and poisonous—Chloroform, sulphuric and nitric ether, +their stimulant, poisonous, and narcotic power—Carbonic acid narcotic, +not quickly poisonous—Concluding remarks.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0010">CHAPTER X.</a><br/> +ON THE SENSITIVENESS OF THE LEAVES, AND ON THE LINES OF TRANSMISSION OF THE MOTOR IMPULSE.<br/> +Glands and summits of the tentacles alone sensitive—Transmission of the +motor impulse down the pedicels of the tentacles, and across the blade of the +leaf—Aggregation of the protoplasm, a reflex action—First discharge +of the motor impulse sudden—Direction of the movements of the +tentacles—Motor impulse transmitted through the cellular tissue— +Mechanism of the movements—Nature of the motor impulse—Re-expansion +of the tentacles.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0011">CHAPTER XI.</a><br/> +RECAPITULATION OF THE CHIEF OBSERVATIONS ON DROSERA ROTUNDIFOLIA.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0012">CHAPTER XII.</a><br/> +ON THE STRUCTURE AND MOVEMENTS OF SOME OTHER SPECIES OF DROSERA.<br/> +Drosera anglica—Drosera intermedia—Drosera capensis—Drosera +spathulata—Drosera filiformis—Drosera binata—Concluding +remarks.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0013">CHAPTER XIII.</a><br/> +DIONAEA MUSCIPULA.<br/> +Structure of the leaves—Sensitiveness of the filaments—Rapid +movement of the lobes caused by irritation of the filaments—Glands, their +power of secretion—Slow movement caused by the absorption of animal +matter—Evidence of absorption from the aggregated condition of the +glands—Digestive power of the secretion—Action of chloroform, +ether, and hydrocyanic acid—The manner in which insects are +captured—Use of the marginal spikes—Kinds of insects +captured—The transmission of the motor impulse and mechanism of the +movements— Re-expansion of the lobes.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0014">CHAPTER XIV.</a><br/> +ALDROVANDA VESICULOSA.<br/> +Captures crustaceans—Structure of the leaves in comparison with those of +Dionaea—Absorption by the glands, by the quadrifid processes, and points +on the infolded margins—Aldrovanda vesiculosa, var. +australis—Captures prey—Absorption of animal +matter—Aldrovanda vesiculosa, var. verticillata—Concluding +remarks.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0015">CHAPTER XV.</a><br/> +DROSOPHYLLUM—RORIDULA—BYBLIS—GLANDULAR HAIRS OF OTHER PLANTS— +CONCLUDING REMARKS ON THE DROSERACEÆ.<br/> +Drosophyllum—Structure of leaves—Nature of the +secretion—Manner of catching insects— Power of +absorption—Digestion of animal substances—Summary on +Drosophyllum—Roridula—Byblis—Glandular hairs of other plants, +their power of absorption—Saxifraga—Primula— +Pelargonium—Erica—Mirabilis—Nicotiana—Summary on +glandular hairs—Concluding remarks on the Droseraceae.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0016">CHAPTER XVI.</a><br/> +PINGUICULA.<br/> +Pinguicula vulgaris—Structure of leaves—Number of insects and other +objects caught—Movement of the margins of the leaves—Uses of this +movement—Secretion, digestion, and absorption—Action of the +secretion on various animal and vegetable substances—The effects of +substances not containing soluble nitrogenous matter on the +glands—Pinguicula grandiflora—Pinguicula lusitanica, catches +insects—Movement of the leaves, secretion and digestion.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0017">CHAPTER XVII.</a><br/> +UTRICULARIA.<br/> +Utricularia neglecta—Structure of the bladder—The uses of the +several parts—Number of imprisoned animals—Manner of +capture—The bladders cannot digest animal matter, but absorb the products +of its decay—Experiments on the absorption of certain fluids by the +quadrifid processes—Absorption by the glands—Summary of the +observation on absorption— Development of the bladders—Utricularia +vulgaris—Utricularia minor—Utricularia +clandestina.<br/><br/> +</p> + +<p class="noindent"> +<a href="#link2HCH0018">CHAPTER XVIII.</a><br/> +UTRICULARIA (continued).<br/> +Utricularia montana—Description of the bladders on the subterranean +rhizomes—Prey captured by the bladders of plants under culture and in a +state of nature—Absorption by the quadrifid processes and +glands—Tubers serving as reservoirs for water—Various other species +of Utricularia—Polypompholyx—Genlisea, different nature of the trap +for capturing prey— Diversified methods by which plants are +nourished. +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2H_4_0002" id="link2H_4_0002"></a> +INSECTIVOROUS PLANTS.</h2> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0001" id="link2HCH0001"></a> +CHAPTER I.<br/> +DROSERA ROTUNDIFOLIA, OR THE COMMON SUN-DEW.</h2> + +<p class="letter"> +Number of insects captured—Description of the leaves and their appendages +or tentacles— Preliminary sketch of the action of the various parts, and +of the manner in which insects are captured—Duration of the inflection of +the tentacles—Nature of the secretion—Manner in which insects are +carried to the centre of the leaf—Evidence that the glands have the power +of absorption—Small size of the roots. +</p> + +<p> +During the summer of 1860, I was surprised by finding how large a number of +insects were caught by the leaves of the common sun-dew (Drosera rotundifolia) +on a heath in Sussex. I had heard that insects were thus caught, but knew +nothing further on the subject.* I +</p> + +<p class="footnote"> +* As Dr. Nitschke has given (‘Bot. Zeitung,’ 1860, p. 229) the +bibliography of Drosera, I need not here go into details. Most of the notices +published before 1860 are brief and unimportant. The oldest paper seems to have +been one of the most valuable, namely, by Dr. Roth, in 1782. There is also an +interesting though short account of the habits of Drosera by Dr. Milde, in the +‘Bot. Zeitung,’ 1852, p. 540. In 1855, in the ‘Annales des +Sc. nat. bot.’ tom. iii. pp. 297 and 304, MM. Groenland and Trcul each +published papers, with figures, on the structure of the leaves; but M. Trcul +went so far as to doubt whether they possessed any power of movement. Dr. +Nitschke’s papers in the ‘Bot. Zeitung’ for 1860 and 1861 are +by far the most important ones which have been published, both on the habits +and structure of this plant; and I shall frequently have occasion to quote from +them. His discussions on several points, for instance on the transmission of an +excitement from one part of the leaf to another, are excellent. On December 11, +1862, Mr. J. Scott read a paper before the Botanical Society of Edinburgh, +[[page 2]] which was published in the ‘Gardeners’ Chronicle,’ +1863, p. 30. Mr. Scott shows that gentle irritation of the hairs, as well as +insects placed on the disc of the leaf, cause the hairs to bend inwards. Mr. +A.W. Bennett also gave another interesting account of the movements of the +leaves before the British Association for 1873. In this same year Dr. Warming +published an essay, in which he describes the structure of the so-called hairs, +entitled, “Sur la Diffrence entre les Trichomes,” &c., +extracted from the proceedings of the Soc. d’Hist. Nat. de Copenhague. I +shall also have occasion hereafter to refer to a paper by Mrs. Treat, of New +Jersey, on some American species of Drosera. Dr. Burdon Sanderson delivered a +lecture on Dionaea, before the Royal Institution published in +‘Nature,’ June 14, 1874, in which a short account of my +observations on the power of true digestion possessed by Drosera and Dionaea +first appeared. Prof. Asa Gray has done good service by calling attention to +Drosera, and to other plants having similar habits, in ‘The Nation’ +(1874, pp. 261 and 232), and in other publications. Dr. Hooker, also, in his +important address on Carnivorous Plants (Brit. Assoc., Belfast, 1874), has +given a history of the subject. [page 2] +</p> + +<p> +gathered by chance a dozen plants, bearing fifty-six fully expanded leaves, and +on thirty-one of these dead insects or remnants of them adhered; and, no doubt, +many more would have been caught afterwards by these same leaves, and still +more by those as yet not expanded. On one plant all six leaves had caught their +prey; and on several plants very many leaves had caught more than a single +insect. On one large leaf I found the remains of thirteen distinct insects. +Flies (Diptera) are captured much oftener than other insects. The largest kind +which I have seen caught was a small butterfly (Caenonympha pamphilus); but the +Rev. H.M. Wilkinson informs me that he found a large living dragon-fly with its +body firmly held by two leaves. As this plant is extremely common in some +districts, the number of insects thus annually slaughtered must be prodigious. +Many plants cause the death of insects, for instance the sticky buds of the +horse-chestnut (Aesculus hippocastanum), without thereby receiving, as far as +we can perceive, any advantage; but it was soon evident that Drosera was [page +3] excellently adapted for the special purpose of catching insects, so that the +subject seemed well worthy of investigation. +</p> + +<p> +The results have proved highly remarkable; the more important ones +being—firstly, the extraordinary +</p> + +<p> +FIG. 1.* (Drosera rotundifolia.) Leaf viewed from above; enlarged four times. +</p> + +<p> +sensitiveness of the glands to slight pressure and to minute doses of certain +nitrogenous fluids, as shown by the movements of the so-called hairs or +tentacles; +</p> + +<p class="footnote"> +* The drawings of Drosera and Dionaea, given in this work, were made for me by +my son George Darwin; those of Aldrovanda, and of the several species of +Utricularia, by my son Francis. They have been excellently reproduced on wood +by Mr. Cooper, 188 Strand. [page 4] +</p> + +<p> +secondly, the power possessed by the leaves of rendering soluble or digesting +nitrogenous substances, and of afterwards absorbing them; thirdly, the changes +which take place within the cells of the tentacles, when the glands are excited +in various ways. +</p> + +<p> +It is necessary, in the first place, to describe briefly the plant. It bears +from two or three to five or six leaves, generally extended more or less +horizontally, but sometimes standing vertically upwards. The shape and general +appearance of a leaf is shown, as seen from above, in fig. 1, and as seen +laterally, in fig. 2. The leaves are commonly a little broader than long, +</p> + +<p> +FIG. 2. (Drosera rotundifolia.) Old leaf viewed laterally; enlarged about five +times. +</p> + +<p> +but this was not the case in the one here figured. The whole upper surface is +covered with gland-bearing filaments, or tentacles, as I shall call them, from +their manner of acting. The glands were counted on thirty-one leaves, but many +of these were of unusually large size, and the average number was 192; the +greatest number being 260, and the least 130. The glands are each surrounded by +large drops of extremely viscid secretion, which, glittering in the sun, have +given rise to the plant’s poetical name of the sun-dew. +</p> + +<p> +[The tentacles on the central part of the leaf or disc are short and stand +upright, and their pedicels are green. Towards the margin they become longer +and longer and more inclined [page 5] outwards, with their pedicels of a purple +colour. Those on the extreme margin project in the same plane with the leaf, or +more commonly (see fig. 2) are considerably reflexed. A few tentacles spring +from the base of the footstalk or petiole, and these are the longest of all, +being sometimes nearly 1/4 of an inch in length. On a leaf bearing altogether +252 tentacles, the short ones on the disc, having green pedicels, were in +number to the longer submarginal and marginal tentacles, having purple +pedicels, as nine to sixteen. +</p> + +<p> +A tentacle consists of a thin, straight, hair-like pedicel, carrying a gland on +the summit. The pedicel is somewhat flattened, and is formed of several rows of +elongated cells, filled with purple fluid or granular matter.* There is, +however, a narrow zone close beneath the glands of the longer tentacles, and a +broader zone near their bases, of a green tint. Spiral vessels, accompanied by +simple vascular tissue, branch off from the vascular bundles in the blade of +the leaf, and run up all the tentacles into the glands. +</p> + +<p> +Several eminent physiologists have discussed the homological nature of these +appendages or tentacles, that is, whether they ought to be considered as hairs +(trichomes) or prolongations of the leaf. Nitschke has shown that they include +all the elements proper to the blade of a leaf; and the fact of their including +vascular tissue was formerly thought to prove that they were prolongations of +the leaf, but it is now known that vessels sometimes enter true hairs.** The +power of movement which they possess is a strong argument against their being +viewed as hairs. The conclusion which seems to me the most probable will be +given in Chap. XV., namely that they existed primordially as glandular hairs, +or mere epidermic formations, and that their upper part should still be so +considered; but that their lower +</p> + +<p class="footnote"> +* According to Nitschke (‘Bot. Zeitung,’ 1861, p. 224) the purple +fluid results from the metamorphosis of chlorophyll. Mr. Sorby examined the +colouring matter with the spectroscope, and informs me that it consists of the +commonest species of erythrophyll, “which is often met with in leaves +with low vitality, and in parts, like the petioles, which carry on +leaf-functions in a very imperfect manner. All that can be said, therefore, is +that the hairs (or tentacles) are coloured like parts of a leaf which do not +fulfil their proper office.” +</p> + +<p class="footnote"> +** Dr. Nitschke has discussed this subject in ‘Bot. Zeitung,’ 1861, +p. 241 &c. See also Dr. Warming (‘Sur la Diffrence entre les +Trichomes’ &c., 1873), who gives references to various publications. +See also Groenland and Trcul ‘Annal. des Sc. nat. bot.’ (4th +series), tom. iii. 1855, pp. 297 and 303. [page 6] +</p> + +<p> +part, which alone is capable of movement, consists of a prolongation of the +leaf; the spiral vessels being extended from this to the uppermost part. We +shall hereafter see that the terminal tentacles of the divided leaves of +Roridula are still in an intermediate condition. +</p> + +<p> +The glands, with the exception of those borne by the extreme +</p> + +<p> +FIG. 3. (Drosera rotundifolia.) Longitudinal section of a gland; greatly +magnified. From Dr. Warming. +</p> + +<p> +marginal tentacles, are oval, and of nearly uniform size, viz. about 4/500 of +an inch in length. Their structure is remarkable, and their functions complex, +for they secrete, absorb, and are acted on by various stimulants. They consist +of an outer layer of small polygonal cells, containing purple granular matter +or fluid, and with the walls thicker than those of the pedicels. [page 7] +Within this layer of cells there is an inner one of differently shaped ones, +likewise filled with purple fluid, but of a slightly different tint, and +differently affected by chloride of gold. These two layers are sometimes well +seen when a gland has been crushed or boiled in caustic potash. According to +Dr. Warming, there is still another layer of much more elongated cells, as +shown in the accompanying section (fig. 3) copied from his work; but these +cells were not seen by Nitschke, nor by me. In the centre there is a group of +elongated, cylindrical cells of unequal lengths, bluntly pointed at their upper +ends, truncated or rounded at their lower ends, closely pressed together, and +remarkable from being surrounded by a spiral line, which can be separated as a +distinct fibre. +</p> + +<p> +These latter cells are filled with limpid fluid, which after long immersion in +alcohol deposits much brown matter. I presume that they are actually connected +with the spiral vessels which run up the tentacles, for on several occasions +the latter were seen to divide into two or three excessively thin branches, +which could be traced close up to the spiriferous cells. Their development has +been described by Dr. Warming. Cells of the same kind have been observed in +other plants, as I hear from Dr. Hooker, and were seen by me in the margins of +the leaves of Pinguicula. Whatever their function may be, they are not +necessary for the secretion of a digestive fluid, or for absorption, or for the +communication of a motor impulse to other parts of the leaf, as we may infer +from the structure of the glands in some other genera of the Droseraceae. +</p> + +<p> +The extreme marginal tentacles differ slightly from the others. Their bases are +broader, and besides their own vessels, they receive a fine branch from those +which enter the tentacles on each side. Their glands are much elongated, and +lie embedded on the upper surface of the pedicel, instead of standing at the +apex. In other respects they do not differ essentially from the oval ones, and +in one specimen I found every possible transition between the two states. In +another specimen there were no long-headed glands. These marginal tentacles +lose their irritability earlier than the others; and when a stimulus is applied +to the centre of the leaf, they are excited into action after the others. When +cut-off leaves are immersed in water, they alone often become inflected. +</p> + +<p> +The purple fluid or granular matter which fills the cells of the glands differs +to a certain extent from that within the cells of the pedicels. For when a leaf +is placed in hot water or in certain acids, the glands become quite white and +opaque, whereas [page 8] the cells of the pedicels are rendered of a bright +red, with the exception of those close beneath the glands. These latter cells +lose their pale red tint; and the green matter which they, as well as the basal +cells, contain, becomes of a brighter green. The petioles bear many +multicellular hairs, some of which near the blade are surmounted, according to +Nitschke, by a few rounded cells, which appear to be rudimentary glands. Both +surfaces of the leaf, the pedicels of the tentacles, especially the lower sides +of the outer ones, and the petioles, are studded with minute papillae (hairs or +trichomes), having a conical basis, and bearing on their summits two, and +occasionally three or even four, rounded cells, containing much protoplasm. +These papillae are generally colourless, but sometimes include a little purple +fluid. They vary in development, and graduate, as Nitschke* states, and as I +repeatedly observed, into the long multicellular hairs. The latter, as well as +the papillae, are probably rudiments of formerly existing tentacles. +</p> + +<p> +I may here add, in order not to recur to the papillae, that they do not +secrete, but are easily permeated by various fluids: thus when living or dead +leaves are immersed in a solution of one part of chloride of gold, or of +nitrate of silver, to 437 of water, they are quickly blackened, and the +discoloration soon spreads to the surrounding tissue. The long multicellular +hairs are not so quickly affected. After a leaf had been left in a weak +infusion of raw meat for 10 hours, the cells of the papillae had evidently +absorbed animal matter, for instead of limpid fluid they now contained small +aggregated masses of protoplasm, which slowly and incessantly changed their +forms. A similar result followed from an immersion of only 15 minutes in a +solution of one part of carbonate of ammonia to 218 of water, and the adjoining +cells of the tentacles, on which the papillae were seated, now likewise +contained aggregated masses of protoplasm. We may therefore conclude that when +a leaf has closely clasped a captured insect in the manner immediately to be +described, the papillae, which project from the upper surface of the leaf and +of the tentacles, probably absorb some of the animal matter dissolved in the +secretion; but this cannot be the case with the papillae on the backs of the +leaves or on the petioles.] +</p> + +<p class="footnote"> +* Nitschke has elaborately described and figured these papillae, ‘Bot. +Zeitung,’ 1861, pp. 234, 253, 254. [page 9] +</p> + +<p class="center"> +<i>Preliminary Sketch of the Action of the several Parts, and of the Manner in +which Insects are Captured.</i> +</p> + +<p> +If a small organic or inorganic object be placed on the glands in the centre of +a leaf, these transmit a motor impulse to the marginal tentacles. The nearer +ones are first affected and slowly bend towards the centre, and then those +farther off, until at last all become closely inflected over the object. This +takes place in from one hour to four or five or more hours. The difference in +the time required depends on many circumstances; namely on the size of the +object and on its nature, that is, whether it contains soluble matter of the +proper kind; on the vigour and age of the leaf; whether it has lately been in +action; and, according to Nitschke,* on the temperature of the day, as likewise +seemed to me to be the case. A living insect is a more efficient object than a +dead one, as in struggling it presses against the glands of many tentacles. An +insect, such as a fly, with thin integuments, through which animal matter in +solution can readily pass into the surrounding dense secretion, is more +efficient in causing prolonged inflection than an insect with a thick coat, +such as a beetle. The inflection of the tentacles takes place indifferently in +the light and darkness; and the plant is not subject to any nocturnal movement +of so-called sleep. +</p> + +<p> +If the glands on the disc are repeatedly touched or brushed, although no object +is left on them, the marginal tentacles curve inwards. So again, if drops of +various fluids, for instance of saliva or of a solution of any salt of ammonia, +are placed on the central glands, the same result quickly follows, sometimes in +under half an hour. +</p> + +<p class="footnote"> +* ‘Bot. Zeitung,’ 1860, p. 246. [page 10] +</p> + +<p> +The tentacles in the act of inflection sweep through a wide space; thus a +marginal tentacle, extended in the same plane with the blade, moves through an +angle of 180o; and I have seen the much reflected tentacles of a leaf which +stood upright move through an angle of not less than 270o. The bending part is +almost confined to a short space near the base; but a rather larger portion of +the elongated exterior tentacles +</p> + +<p> +FIG. 4. (Drosera rotundifolia.) Leaf (enlarged) with all the tentacles closely +inflected, from immersion in a solution of phosphate of ammonia (one part to +87,500 of water.) +</p> + +<p> +FIG. 5. (Drosera rotundifolia.) Leaf (enlarged) with the tentacles on one side +inflected over a bit of meat placed on the disc. +</p> + +<p> +becomes slightly incurved; the distal half in all cases remaining straight. The +short tentacles in the centre of the disc when directly excited, do not become +inflected; but they are capable of inflection if excited by a motor impulse +received from other glands at a distance. Thus, if a leaf is immersed in an +infusion of raw meat, or in a weak solution of ammonia (if the [page 11] +solution is at all strong, the leaf is paralysed), all the exterior tentacles +bend inwards (see fig. 4), excepting those near the centre, which remain +upright; but these bend towards any exciting object placed on one side of the +disc, as shown in fig. 5. The glands in fig. 4 may be seen to form a dark ring +round the centre; and this follows from the exterior tentacles increasing in +length in due proportion, as they stand nearer to the circumference. +</p> + +<p> +The kind of inflection which the tentacles undergo is best shown when the gland +of one of the long exterior +</p> + +<p> +FIG. 6. (Drosera rotundifolia.) Diagram showing one of the exterior tentacles +closely inflected; the two adjoining ones in their ordinary position.) +</p> + +<p> +tentacles is in any way excited; for the surrounding ones remain unaffected. In +the accompanying outline (fig. 6) we see one tentacle, on which a particle of +meat had been placed, thus bent towards the centre of the leaf, with two others +retaining their original position. A gland may be excited by being simply +touched three or four times, or by prolonged contact with organic or inorganic +objects, and various fluids. I have distinctly seen, through a lens, a tentacle +beginning to bend in ten seconds, after an object had been [page 12] placed on +its gland; and I have often seen strongly pronounced inflection in under one +minute. It is surprising how minute a particle of any substance, such as a bit +of thread or hair or splinter of glass, if placed in actual contact with the +surface of a gland, suffices to cause the tentacle to bend. If the object, +which has been carried by this movement to the centre, be not very small, or if +it contains soluble nitrogenous matter, it acts on the central glands; and +these transmit a motor impulse to the exterior tentacles, causing them to bend +inwards. +</p> + +<p> +Not only the tentacles, but the blade of the leaf often, but by no means +always, becomes much incurved, when any strongly exciting substance or fluid is +placed on the disc. Drops of milk and of a solution of nitrate of ammonia or +soda are particularly apt to produce this effect. The blade is thus converted +into a little cup. The manner in which it bends varies greatly. Sometimes the +apex alone, sometimes one side, and sometimes both sides, become incurved. For +instance, I placed bits of hard-boiled egg on three leaves; one had the apex +bent towards the base; the second had both distal margins much incurved, so +that it became almost triangular in outline, and this perhaps is the commonest +case; whilst the third blade was not at all affected, though the tentacles were +as closely inflected as in the two previous cases. The whole blade also +generally rises or bends upwards, and thus forms a smaller angle with the +footstalk than it did before. This appears at first sight a distinct kind of +movement, but it results from the incurvation of that part of the margin which +is attached to the footstalk, causing the blade, as a whole, to curve or move +upwards. +</p> + +<p> +The length of time during which the tentacles as [page 13] well as the blade +remain inflected over an object placed on the disc, depends on various +circumstances; namely on the vigour and age of the leaf, and, according to Dr. +Nitschke, on the temperature, for during cold weather when the leaves are +inactive, they re-expand at an earlier period than when the weather is warm. +But the nature of the object is by far the most important circumstance; I have +repeatedly found that the tentacles remain clasped for a much longer average +time over objects which yield soluble nitrogenous matter than over those, +whether organic or inorganic, which yield no such matter. After a period +varying from one to seven days, the tentacles and blade re-expand, and are then +ready to act again. I have seen the same leaf inflected three successive times +over insects placed on the disc; and it would probably have acted a greater +number of times. +</p> + +<p> +The secretion from the glands is extremely viscid, so that it can be drawn out +into long threads. It appears colourless, but stains little balls of paper pale +pink. An object of any kind placed on a gland always causes it, as I believe, +to secrete more freely; but the mere presence of the object renders this +difficult to ascertain. In some cases, however, the effect was strongly marked, +as when particles of sugar were added; but the result in this case is probably +due merely to exosmose. Particles of carbonate and phosphate of ammonia and of +some other salts, for instance sulphate of zinc, likewise increase the +secretion. Immersion in a solution of one part of chloride of gold, or of some +other salts, to 437 of water, excites the glands to largely increased +secretion; on the other hand, tartrate of antimony produces no such effect. +Immersion in many acids (of the strength of one part to 437 of water) likewise +causes a wonderful amount of [page 14] secretion, so that when the leaves are +lifted out, long ropes of extremely viscid fluid hang from them. Some acids, on +the other hand, do not act in this manner. Increased secretion is not +necessarily dependent on the inflection of the tentacle, for particles of sugar +and of sulphate of zinc cause no movement. +</p> + +<p> +It is a much more remarkable fact that when an object, such as a bit of meat or +an insect, is placed on the disc of a leaf, as soon as the surrounding +tentacles become considerably inflected, their glands pour forth an increased +amount of secretion. I ascertained this by selecting leaves with equal-sized +drops on the two sides, and by placing bits of meat on one side of the disc; +and as soon as the tentacles on this side became much inflected, but before the +glands touched the meat, the drops of secretion became larger. This was +repeatedly observed, but a record was kept of only thirteen cases, in nine of +which increased secretion was plainly observed; the four failures being due +either to the leaves being rather torpid, or to the bits of meat being too +small to cause much inflection. We must therefore conclude that the central +glands, when strongly excited, transmit some influence to the glands of the +circumferential tentacles, causing them to secrete more copiously. +</p> + +<p> +It is a still more important fact (as we shall see more fully when we treat of +the digestive power of the secretion) that when the tentacles become inflected, +owing to the central glands having been stimulated mechanically, or by contact +with animal matter, the secretion not only increases in quantity, but changes +its nature and becomes acid; and this occurs before the glands have touched the +object on the centre of the leaf. This acid is of a different nature from that +contained in the tissue of the leaves. As long as the [page 15] tentacles +remain closely inflected, the glands continue to secrete, and the secretion is +acid; so that, if neutralised by carbonate of soda, it again becomes acid after +a few hours. I have observed the same leaf with the tentacles closely inflected +over rather indigestible substances, such as chemically prepared casein, +pouring forth acid secretion for eight successive days, and over bits of bone +for ten successive days. +</p> + +<p> +The secretion seems to possess, like the gastric juice of the higher animals, +some antiseptic power. During very warm weather I placed close together two +equal-sized bits of raw meat, one on a leaf of the Drosera, and the other +surrounded by wet moss. They were thus left for 48 hrs., and then examined. The +bit on the moss swarmed with infusoria, and was so much decayed that the +transverse striae on the muscular fibres could no longer be clearly +distinguished; whilst the bit on the leaf, which was bathed by the secretion, +was free from infusoria, and its striae were perfectly distinct in the central +and undissolved portion. In like manner small cubes of albumen and cheese +placed on wet moss became threaded with filaments of mould, and had their +surfaces slightly discoloured and disintegrated; whilst those on the leaves of +Drosera remained clean, the albumen being changed into transparent fluid. +</p> + +<p> +As soon as tentacles, which have remained closely inflected during several days +over an object, begin to re-expand, their glands secrete less freely, or cease +to secrete, and are left dry. In this state they are covered with a film of +whitish, semi-fibrous matter, which was held in solution by the secretion. The +drying of the glands during the act of re-expansion is of some little service +to the plant; for I have often observed that objects adhering to the leaves +[page 16] could then be blown away by a breath of air; the leaves being thus +left unencumbered and free for future action. Nevertheless, it often happens +that all the glands do not become completely dry; and in this case delicate +objects, such as fragile insects, are sometimes torn by the re-expansion of the +tentacles into fragments, which remain scattered all over the leaf. After the +re-expansion is complete, the glands quickly begin to re-secrete, and as soon +as full-sized drops are formed, the tentacles are ready to clasp a new object. +</p> + +<p> +When an insect alights on the central disc, it is instantly entangled by the +viscid secretion, and the surrounding tentacles after a time begin to bend, and +ultimately clasp it on all sides. Insects are generally killed, according to +Dr. Nitschke, in about a quarter of an hour, owing to their tracheae being +closed by the secretion. If an insect adheres to only a few of the glands of +the exterior tentacles, these soon become inflected and carry their prey to the +tentacles next succeeding them inwards; these then bend inwards, and so +onwards; until the insect is ultimately carried by a curious sort of rolling +movement to the centre of the leaf. Then, after an interval, the tentacles on +all sides become inflected and bathe their prey with their secretion, in the +same manner as if the insect had first alighted on the central disc. It is +surprising how minute an insect suffices to cause this action: for instance, I +have seen one of the smallest species of gnats (Culex), which had just settled +with its excessively delicate feet on the glands of the outermost tentacles, +and these were already beginning to curve inwards, though not a single gland +had as yet touched the body of the insect. Had I not interfered, this minute +gnat would [page 17] assuredly have been carried to the centre of the leaf and +been securely clasped on all sides. We shall hereafter see what excessively +small doses of certain organic fluids and saline solutions cause strongly +marked inflection. +</p> + +<p> +Whether insects alight on the leaves by mere chance, as a resting place, or are +attracted by the odour of the secretion, I know not. I suspect from the number +of insects caught by the English species of Drosera, and from what I have +observed with some exotic species kept in my greenhouse, that the odour is +attractive. In this latter case the leaves may be compared with a baited trap; +in the former case with a trap laid in a run frequented by game, but without +any bait. +</p> + +<p> +That the glands possess the power of absorption, is shown by their almost +instantaneously becoming dark-coloured when given a minute quantity of +carbonate of ammonia; the change of colour being chiefly or exclusively due to +the rapid aggregation of their contents. When certain other fluids are added, +they become pale-coloured. Their power of absorption is, however, best shown by +the widely different results which follow, from placing drops of various +nitrogenous and non-nitrogenous fluids of the same density on the glands of the +disc, or on a single marginal gland; and likewise by the very different lengths +of time during which the tentacles remain inflected over objects, which yield +or do not yield soluble nitrogenous matter. This same conclusion might indeed +have been inferred from the structure and movements of the leaves, which are so +admirably adapted for capturing insects. +</p> + +<p> +The absorption of animal matter from captured insects explains how Drosera can +flourish in extremely poor peaty soil,—in some cases where nothing but +[page 18] sphagnum moss grows, and mosses depend altogether on the atmosphere +for their nourishment. Although the leaves at a hasty glance do not appear +green, owing to the purple colour of the tentacles, yet the upper and lower +surfaces of the blade, the pedicels of the central tentacles, and the petioles +contain chlorophyll, so that, no doubt, the plant obtains and assimilates +carbonic acid from the air. Nevertheless, considering the nature of the soil +where it grows, the supply of nitrogen would be extremely limited, or quite +deficient, unless the plant had the power of obtaining this important element +from captured insects. We can thus understand how it is that the roots are so +poorly developed. These usually consist of only two or three slightly divided +branches, from half to one inch in length, furnished with absorbent hairs. It +appears, therefore, that the roots serve only to imbibe water; though, no +doubt, they would absorb nutritious matter if present in the soil; for as we +shall hereafter see, they absorb a weak solution of carbonate of ammonia. A +plant of Drosera, with the edges of its leaves curled inwards, so as to form a +temporary stomach, with the glands of the closely inflected tentacles pouring +forth their acid secretion, which dissolves animal matter, afterwards to be +absorbed, may be said to feed like an animal. But, differently from an animal, +it drinks by means of its roots; and it must drink largely, so as to retain +many drops of viscid fluid round the glands, sometimes as many as 260, exposed +during the whole day to a glaring sun. [page 19] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0002" id="link2HCH0002"></a> +CHAPTER II.<br/> +THE MOVEMENTS OF THE TENTACLES FROM THE CONTACT OF SOLID BODIES.</h2> + +<p class="letter"> +Inflection of the exterior tentacles owing to the glands of the disc being +excited by repeated touches, or by objects left in contact with +them—Difference in the action of bodies yielding and not yielding soluble +nitrogenous matter—Inflection of the exterior tentacles directly caused +by objects left in contact with their glands—Periods of commencing +inflection and of subsequent re-expansion—Extreme minuteness of the +particles causing inflection—Action under water—Inflection of the +exterior tentacles when their glands are excited by repeated +touches—Falling drops of water do not cause inflection. +</p> + +<p> +I will give in this and the following chapters some of the many experiments +made, which best illustrate the manner and rate of movement of the tentacles, +when excited in various ways. The glands alone in all ordinary cases are +susceptible to excitement. When excited, they do not themselves move or change +form, but transmit a motor impulse to the bending part of their own and +adjoining tentacles, and are thus carried towards the centre of the leaf. +Strictly speaking, the glands ought to be called irritable, as the term +sensitive generally implies consciousness; but no one supposes that the +Sensitive-plant is conscious, and as I have found the term convenient, I shall +use it without scruple. I will commence with the movements of the exterior +tentacles, when indirectly excited by stimulants applied to the glands of the +short tentacles on the disc. The exterior tentacles may be said in this case to +be indirectly excited, because their own glands are not directly acted on. The +stimulus proceeding from the glands of the disc acts on the bending part of the +[page 20] exterior tentacles, near their bases, and does not (as will hereafter +be proved) first travel up the pedicels to the glands, to be then reflected +back to the bending place. Nevertheless, some influence does travel up to the +glands, causing them to secrete more copiously, and the secretion to become +acid. This latter fact is, I believe, quite new in the physiology of plants; it +has indeed only recently been established that in the animal kingdom an +influence can be transmitted along the nerves to glands, modifying their power +of secretion, independently of the state of the blood-vessels. +</p> + +<p> +The Inflection of the Exterior Tentacles from the Glands of the Disc being +excited by Repeated Touches, or by Objects left in Contact with them. +</p> + +<p> +The central glands of a leaf were irritated with a small stiff camel-hair +brush, and in 70 m. (minutes) several of the outer tentacles were inflected; in +5 hrs. (hours) all the sub-marginal tentacles were inflected; next morning +after an interval of about 22 hrs. they were fully re-expanded. In all the +following cases the period is reckoned from the time of first irritation. +Another leaf treated in the same manner had a few tentacles inflected in 20 m.; +in 4 hrs. all the submarginal and some of the extreme marginal tentacles, as +well as the edge of the leaf itself, were inflected; in 17 hrs. they had +recovered their proper, expanded position. I then put a dead fly in the centre +of the last-mentioned leaf, and next morning it was closely clasped; five days +afterwards the leaf re-expanded, and the tentacles, with their glands +surrounded by secretion, were ready to act again. +</p> + +<p> +Particles of meat, dead flies, bits of paper, wood, dried moss, sponge, +cinders, glass, &c., were repeatedly [page 21] placed on leaves, and these +objects were well embraced in various periods from one hr. to as long as 24 +hrs., and set free again, with the leaf fully re-expanded, in from one or two, +to seven or even ten days, according to the nature of the object. On a leaf +which had naturally caught two flies, and therefore had already closed and +reopened either once or more probably twice, I put a fresh fly: in 7 hrs. it +was moderately, and in 21 hrs. thoroughly well, clasped, with the edges of the +leaf inflected. In two days and a half the leaf had nearly re-expanded; as the +exciting object was an insect, this unusually short period of inflection was, +no doubt, due to the leaf having recently been in action. Allowing this same +leaf to rest for only a single day, I put on another fly, and it again closed, +but now very slowly; nevertheless, in less than two days it succeeded in +thoroughly clasping the fly. +</p> + +<p> +When a small object is placed on the glands of the disc, on one side of a leaf, +as near as possible to its circumference, the tentacles on this side are first +affected, those on the opposite side much later, or, as often occurred, not at +all. This was repeatedly proved by trials with bits of meat; but I will here +give only the case of a minute fly, naturally caught and still alive, which I +found adhering by its delicate feet to the glands on the extreme left side of +the central disc. The marginal tentacles on this side closed inwards and killed +the fly, and after a time the edge of the leaf on this side also became +inflected, and thus remained for several days, whilst neither the tentacles nor +the edge on the opposite side were in the least affected. +</p> + +<p> +If young and active leaves are selected, inorganic particles not larger than +the head of a small pin, placed on the central glands, sometimes cause the +[page 22] outer tentacles to bend inwards. But this follows much more surely +and quickly, if the object contains nitrogenous matter which can be dissolved +by the secretion. On one occasion I observed the following unusual +circumstance. Small bits of raw meat (which acts more energetically than any +other substance), of paper, dried moss, and of the quill of a pen were placed +on several leaves, and they were all embraced equally well in about 2 hrs. On +other occasions the above-named substances, or more commonly particles of +glass, coal-cinder (taken from the fire), stone, gold-leaf, dried grass, cork, +blotting-paper, cotton-wool, and hair rolled up into little balls, were used, +and these substances, though they were sometimes well embraced, often caused no +movement whatever in the outer tentacles, or an extremely slight and slow +movement. Yet these same leaves were proved to be in an active condition, as +they were excited to move by substances yielding soluble nitrogenous matter, +such as bits of raw or roast meat, the yolk or white of boiled eggs, fragments +of insects of all orders, spiders, &c. I will give only two instances. +Minute flies were placed on the discs of several leaves, and on others balls of +paper, bits of moss and quill of about the same size as the flies, and the +latter were well embraced in a few hours; whereas after 25 hrs. only a very few +tentacles were inflected over the other objects. The bits of paper, moss, and +quill were then removed from these leaves, and bits of raw meat placed on them; +and now all the tentacles were soon energetically inflected. +</p> + +<p> +Again, particles of coal-cinder (weighing rather more than the flies used in +the last experiment) were placed on the centres of three leaves: after an +interval of 19 hrs. one of the particles was tolerably well embraced; [page 23] +a second by a very few tentacles; and a third by none. I then removed the +particles from the two latter leaves, and put on them recently killed flies. +These were fairly well embraced in 7 1/2 hrs. and thoroughly after 20 1/2 hrs.; +the tentacles remaining inflected for many subsequent days. On the other hand, +the one leaf which had in the course of 19 hrs. embraced the bit of cinder +moderately well, and to which no fly was given, after an additional 33 hrs. +(i.e. in 52 hrs. from the time when the cinder was put on) was completely +re-expanded and ready to act again. +</p> + +<p> +From these and numerous other experiments not worth giving, it is certain that +inorganic substances, or such organic substances as are not attacked by the +secretion, act much less quickly and efficiently than organic substances +yielding soluble matter which is absorbed. Moreover, I have met with very few +exceptions to the rule, and these exceptions apparently depended on the leaf +having been too recently in action, that the tentacles remain clasped for a +much longer time over organic bodies of the nature just specified than over +those which are not acted on by the secretion, or over inorganic objects.* +</p> + +<p class="footnote"> +* Owing to the extraordinary belief held by M. Ziegler (‘Comptes +rendus,’ May 1872, p. 122), that albuminous substances, if held for a +moment between the fingers, acquire the property of making the tentacles of +Drosera contract, whereas, if not thus held, they have no such power, I tried +some experiments with great care, but the results did not confirm this belief. +Red-hot cinders were taken out of the fire, and bits of glass, cotton-thread, +blotting paper and thin slices of cork were immersed in boiling water; and +particles were then placed (every instrument with which they were touched +having been previously immersed in boiling water) on the glands of several +leaves, and they acted in exactly the same manner as other particles, which had +been purposely handled for some time. Bits of a boiled egg, cut with a knife +which had been washed in boiling water, also acted like any other animal +substance. I breathed on some leaves for above a minute, and repeated the act +two or three times, with my mouth close to [[page 24]] them, but this produced +no effect. I may here add, as showing that the leaves are not acted on by the +odour of nitrogenous substances, that pieces of raw meat stuck on needles were +fixed as close as possible, without actual contact, to several leaves, but +produced no effect whatever. On the other hand, as we shall hereafter see, the +vapours of certain volatile substances and fluids, such as of carbonate of +ammonia, chloroform, certain essential oils, &c., cause inflection. M. +Ziegler makes still more extraordinary statements with respect to the power of +animal substances, which have been left close to, but not in contact with, +sulphate of quinine. The action of salts of quinine will be described in a +future chapter. Since the appearance of the paper above referred to, M. Ziegler +has published a book on the same subject, entitled ‘Atonicit et +Zoicit,’ 1874.) [page 24] +</p> + +<p> +The Inflection of the Exterior Tentacles as directly caused by Objects left in +Contact with their Glands. +</p> + +<p> +I made a vast number of trials by placing, by means of a fine needle moistened +with distilled water, and with the aid of a lens, particles of various +substances on the viscid secretion surrounding the glands of the outer +tentacles. I experimented on both the oval and long-headed glands. When a +particle is thus placed on a single gland, the movement of the tentacle is +particularly well seen in contrast with the stationary condition of the +surrounding tentacles. (See previous fig. 6.) In four cases small particles of +raw meat caused the tentacles to be greatly inflected in between 5 and 6 m. +Another tentacle similarly treated, and observed with special care, distinctly, +though slightly, changed its position in 10 s. (seconds); and this is the +quickest movement seen by me. In 2 m. 30 s. it had moved through an angle of +about 45o. The movement as seen through a lens resembled that of the hand of a +large clock. In 5 m. it had moved through 90o, and when I looked again after 10 +m., the particle had reached the centre of the leaf; so that the whole movement +was completed in less [page 25] than 17 m. 30 s. In the course of some hours +this minute bit of meat, from having been brought into contact with some of the +glands of the central disc, acted centrifugally on the outer tentacles, which +all became closely inflected. Fragments of flies were placed on the glands of +four of the outer tentacles, extended in the same plane with that of the blade, +and three of these fragments were carried in 35 m. through an angle of 180o to +the centre. The fragment on the fourth tentacle was very minute, and it was not +carried to the centre until 3 hrs. had elapsed. In three other cases minute +flies or portions of larger ones were carried to the centre in 1 hr. 30 s. In +these seven cases, the fragments or small flies, which had been carried by a +single tentacle to the central glands, were well embraced by the other +tentacles after an interval of from 4 to 10 hrs. +</p> + +<p> +I also placed in the manner just described six small balls of writing-paper +(rolled up by the aid of pincers, so that they were not touched by my fingers) +on the glands of six exterior tentacles on distinct leaves; three of these were +carried to the centre in about 1 hr., and the other three in rather more than 4 +hrs.; but after 24 hrs. only two of the six balls were well embraced by the +other tentacles. It is possible that the secretion may have dissolved a trace +of glue or animalised matter from the balls of paper. Four particles of +coal-cinder were then placed on the glands of four exterior tentacles; one of +these reached the centre in 3 hrs. 40 m.; the second in 9 hrs.; the third +within 24 hrs., but had moved only part of the way in 9 hrs.; whilst the fourth +moved only a very short distance in 24 hrs., and never moved any farther. Of +the above three bits of cinder which were ultimately carried to the centre, one +alone was well embraced by [page 26] many of the other tentacles. We here see +clearly that such bodies as particles of cinder or little balls of paper, after +being carried by the tentacles to the central glands, act very differently from +fragments of flies, in causing the movement of the surrounding tentacles. +</p> + +<p> +I made, without carefully recording the times of movement, many similar trials +with other substances, such as splinters of white and blue glass, particles of +cork, minute bits of gold-leaf, &c.; and the proportional number of cases +varied much in which the tentacles reached the centre, or moved only slightly, +or not at all. One evening, particles of glass and cork, rather larger than +those usually employed, were placed on about a dozen glands, and next morning, +after 13 hrs., every single tentacle had carried its little load to the centre; +but the unusually large size of the particles will account for this result. In +another case 6/7 of the particles of cinder, glass, and thread, placed on +separate glands, were carried towards, or actually to, the centre; in another +case 7/9, in another 7/12, and in the last case only 7/26 were thus carried +inwards, the small proportion being here due, at least in part, to the leaves +being rather old and inactive. Occasionally a gland, with its light load, could +be seen through a strong lens to move an extremely short distance and then +stop; this was especially apt to occur when excessively minute particles, much +less than those of which the measurements will be immediately given, were +placed on glands; so that we here have nearly the limit of any action. +</p> + +<p> +I was so much surprised at the smallness of the particles which caused the +tentacles to become greatly inflected that it seemed worth while carefully to +ascertain how minute a particle would plainly act. [page 27] Accordingly +measured lengths of a narrow strip of blotting paper, of fine cotton-thread, +and of a woman’s hair, were carefully weighed for me by Mr. Trenham +Reeks, in an excellent balance, in the laboratory in Jermyn Street. Short bits +of the paper, thread, and hair were then cut off and measured by a micrometer, +so that their weights could be easily calculated. The bits were placed on the +viscid secretion surrounding the glands of the exterior tentacles, with the +precautions already stated, and I am certain that the gland itself was never +touched; nor indeed would a single touch have produced any effect. A bit of the +blotting-paper, weighing 1/465 of a grain, was placed so as to rest on three +glands together, and all three tentacles slowly curved inwards; each gland, +therefore, supposing the weight to be distributed equally, could have been +pressed on by only 1/1395 of a grain, or .0464 of a milligramme. Five nearly +equal bits of cotton-thread were tried, and all acted. The shortest of these +was 1/50 of an inch in length, and weighed 1/8197 of a grain. The tentacle in +this case was considerably inflected in 1 hr. 30 m., and the bit of thread was +carried to the centre of the leaf in 1 hr. 40 m. Again, two particles of the +thinner end of a woman’s hair, one of these being 18/1000 of an inch in +length, and weighing 1/35714 of a grain, the other 19/1000 of an inch in +length, and weighing of course a little more, were placed on two glands on +opposite sides of the same leaf, and these two tentacles were inflected halfway +towards the centre in 1 hr. 10 m.; all the many other tentacles round the same +leaf remaining motionless. The appearance of this one leaf showed in an +unequivocal manner that these minute particles sufficed to cause the tentacles +to bend. Altogether, ten such particles of hair were placed on ten glands on +several leaves, and seven of them caused [page 28] the tentacles to move in a +conspicuous manner. The smallest particle which was tried, and which acted +plainly, was only 8/1000 of an inch (.203 millimetre) in length, and weighed +the 1/78740 of a grain, or .000822 milligramme. In these several cases, not +only was the inflection of the tentacles conspicuous, but the purple fluid +within their cells became aggregated into little masses of protoplasm, in the +manner to be described in the next chapter; and the aggregation was so plain +that I could, by this clue alone, have readily picked out under the microscope +all the tentacles which had carried their light loads towards the centre, from +the hundreds of other tentacles on the same leaves which had not thus acted. +</p> + +<p> +My surprise was greatly excited, not only by the minuteness of the particles +which caused movement, but how they could possibly act on the glands; for it +must be remembered that they were laid with the greatest care on the convex +surface of the secretion. At first I thought—but, as I now know, +erroneously—that particles of such low specific gravity as those of cork, +thread, and paper, would never come into contact with the surfaces of the +glands. The particles cannot act simply by their weight being added to that of +the secretion, for small drops of water, many times heavier than the particles, +were repeatedly added, and never produced any effect. Nor does the disturbance +of the secretion produce any effect, for long threads were drawn out by a +needle, and affixed to some adjoining object, and thus left for hours; but the +tentacles remained motionless. +</p> + +<p> +I also carefully removed the secretion from four glands with a sharply pointed +piece of blotting-paper, so that they were exposed for a time naked to the air, +but this caused no movement; yet these glands were [page 29] in an efficient +state, for after 24 hrs. had elapsed, they were tried with bits of meat, and +all became quickly inflected. It then occurred to me that particles floating on +the secretion would cast shadows on the glands, which might be sensitive to the +interception of the light. Although this seemed highly improbable, as minute +and thin splinters of colourless glass acted powerfully, nevertheless, after it +was dark, I put on, by the aid of a single tallow candle, as quickly as +possible, particles of cork and glass on the glands of a dozen tentacles, as +well as some of meat on other glands, and covered them up so that not a ray of +light could enter; but by the next morning, after an interval of 13 hrs., all +the particles were carried to the centres of the leaves. +</p> + +<p> +These negative results led me to try many more experiments, by placing +particles on the surface of the drops of secretion, observing, as carefully as +I could, whether they penetrated it and touched the surface of the glands. The +secretion, from its weight, generally forms a thicker layer on the under than +on the upper sides of the glands, whatever may be the position of the +tentacles. Minute bits of dry cork, thread, blotting paper, and coal cinders +were tried, such as those previously employed; and I now observed that they +absorbed much more of the secretion, in the course of a few minutes, than I +should have thought possible; and as they had been laid on the upper surface of +the secretion, where it is thinnest, they were often drawn down, after a time, +into contact with at least some one point of the gland. With respect to the +minute splinters of glass and particles of hair, I observed that the secretion +slowly spread itself a little over their surfaces, by which means they were +likewise drawn downwards or sideways, and thus one end, or some minute [page +30] prominence, often came to touch, sooner or later, the gland. +</p> + +<p> +In the foregoing and following cases, it is probable that the vibrations, to +which the furniture in every room is continually liable, aids in bringing the +particles into contact with the glands. But as it was sometimes difficult, +owing to the refraction of the secretion, to feel sure whether the particles +were in contact, I tried the following experiment. Unusually minute particles +of glass, hair, and cork, were gently placed on the drops round several glands, +and very few of the tentacles moved. Those which were not affected were left +for about half an hour, and the particles were then disturbed or tilted up +several times with a fine needle under the microscope, the glands not being +touched. And now in the course of a few minutes almost all the hitherto +motionless tentacles began to move; and this, no doubt, was caused by one end +or some prominence of the particles having come into contact with the surface +of the glands. But as the particles were unusually minute, the movement was +small. +</p> + +<p> +Lastly, some dark blue glass pounded into fine splinters was used, in order +that the points of the particles might be better distinguished when immersed in +the secretion; and thirteen such particles were placed in contact with the +depending and therefore thicker part of the drops round so many glands. Five of +the tentacles began moving after an interval of a few minutes, and in these +cases I clearly saw that the particles touched the lower surface of the gland. +A sixth tentacle moved after 1 hr. 45 m., and the particle was now in contact +with the gland, which was not the case at first. So it was with the seventh +tentacle, but its movement did not begin until 3 hrs. 45 m. had [page 31] +elapsed. The remaining six tentacles never moved as long as they were observed; +and the particles apparently never came into contact with the surfaces of the +glands. +</p> + +<p> +From these experiments we learn that particles not containing soluble matter, +when placed on glands, often cause the tentacles to begin bending in the course +of from one to five minutes; and that in such cases the particles have been +from the first in contact with the surfaces of the glands. When the tentacles +do not begin moving for a much longer time, namely, from half an hour to three +or four hours, the particles have been slowly brought into contact with the +glands, either by the secretion being absorbed by the particles or by its +gradual spreading over them, together with its consequent quicker evaporation. +When the tentacles do not move at all, the particles have never come into +contact with the glands, or in some cases the tentacles may not have been in an +active condition. In order to excite movement, it is indispensable that the +particles should actually rest on the glands; for a touch once, twice, or even +thrice repeated by any hard body is not sufficient to excite movement. +</p> + +<p> +Another experiment, showing that extremely minute particles act on the glands +when immersed in water, may here be given. A grain of sulphate of quinine was +added to an ounce of water, which was not afterwards filtered; and on placing +three leaves in ninety minims of this fluid, I was much surprised to find that +all three leaves were greatly inflected in 15 m.; for I knew from previous +trials that the solution does not act so quickly as this. It immediately +occurred to me that the particles of the undissolved salt, which were so light +as to float about, might have come [page 32] into contact with the glands, and +caused this rapid movement. Accordingly I added to some distilled water a pinch +of a quite innocent substance, namely, precipitated carbonate of lime, which +consists of an impalpable powder; I shook the mixture, and thus got a fluid +like thin milk. Two leaves were immersed in it, and in 6 m. almost every +tentacle was much inflected. I placed one of these leaves under the microscope, +and saw innumerable atoms of lime adhering to the external surface of the +secretion. Some, however, had penetrated it, and were lying on the surfaces of +the glands; and no doubt it was these particles which caused the tentacles to +bend. When a leaf is immersed in water, the secretion instantly swells much; +and I presume that it is ruptured here and there, so that little eddies of +water rush in. If so, we can understand how the atoms of chalk, which rested on +the surfaces of the glands, had penetrated the secretion. Anyone who has rubbed +precipitated chalk between his fingers will have perceived how excessively fine +the powder is. No doubt there must be a limit, beyond which a particle would be +too small to act on a gland; but what this limit is, I know not. I have often +seen fibres and dust, which had fallen from the air, on the glands of plants +kept in my room, and these never induced any movement; but then such particles +lay on the surface of the secretion and never reached the gland itself. +</p> + +<p> +Finally, it is an extraordinary fact that a little bit of soft thread, 1/50 of +an inch in length and weighing 1/8197 of a grain, or of a human hair, 8/1000 of +an inch in length and weighing only 1/78740 of a grain (.000822 milligramme), +or particles of precipitated chalk, after resting for a short time on a gland, +should induce some change in its cells, exciting them [page 33] to transmit a +motor impulse throughout the whole length of the pedicel, consisting of about +twenty cells, to near its base, causing this part to bend, and the tentacle to +sweep through an angle of above 180o. That the contents of the cells of the +glands, and afterwards those of the pedicels, are affected in a plainly visible +manner by the pressure of minute particles, we shall have abundant evidence +when we treat of the aggregation of protoplasm. But the case is much more +remarkable than as yet stated; for the particles are supported by the viscid +and dense secretion; nevertheless, even smaller ones than those of which the +measurements have been given, when brought by an insensibly slow movement, +through the means above specified, into contact with the surface of a gland, +act on it, and the tentacle bends. The pressure exerted by the particle of +hair, weighing only 1/78740 of a grain and supported by a dense fluid, must +have been inconceivably slight. We may conjecture that it could hardly have +equalled the millionth of a grain; and we shall hereafter see that far less +than the millionth of a grain of phosphate of ammonia in solution, when +absorbed by a gland, acts on it and induces movement. A bit of hair, 1/50 of an +inch in length, and therefore much larger than those used in the above +experiments, was not perceived when placed on my tongue; and it is extremely +doubtful whether any nerve in the human body, even if in an inflamed condition, +would be in any way affected by such a particle supported in a dense fluid, and +slowly brought into contact with the nerve. Yet the cells of the glands of +Drosera are thus excited to transmit a motor impulse to a distant point, +inducing movement. It appears to me that hardly any more remarkable fact than +this has been observed in the vegetable kingdom. [page 34] +</p> + +<p> +The Inflection of the Exterior Tentacles, when their Glands are excited by +Repeated Touches. +</p> + +<p> +We have already seen that, if the central glands are excited by being gently +brushed, they transmit a motor impulse to the exterior tentacles, causing them +to bend; and we have now to consider the effects which follow from the glands +of the exterior tentacles being themselves touched. On several occasions, a +large number of glands were touched only once with a needle or fine brush, hard +enough to bend the whole flexible tentacle; and though this must have caused a +thousand-fold greater pressure than the weight of the above described +particles, not a tentacle moved. On another occasion forty-five glands on +eleven leaves were touched once, twice, or even thrice, with a needle or stiff +bristle. This was done as quickly as possible, but with force sufficient to +bend the tentacles; yet only six of them became inflected,—three plainly, +and three in a slight degree. In order to ascertain whether these tentacles +which were not affected were in an efficient state, bits of meat were placed on +ten of them, and they all soon became greatly incurved. On the other hand, when +a large number of glands were struck four, five, or six times with the same +force as before, a needle or sharp splinter of glass being used, a much larger +proportion of tentacles became inflected; but the result was so uncertain as to +seem capricious. For instance, I struck in the above manner three glands, which +happened to be extremely sensitive, and all three were inflected almost as +quickly, as if bits of meat had been placed on them. On another occasion I gave +a single for- [page 35] cible touch to a considerable number of glands, and not +one moved; but these same glands, after an interval of some hours, being +touched four or five times with a needle, several of the tentacles soon became +inflected. +</p> + +<p> +The fact of a single touch or even of two or three touches not causing +inflection must be of some service to the plant; as during stormy weather, the +glands cannot fail to be occasionally touched by the tall blades of grass, or +by other plants growing near; and it would be a great evil if the tentacles +were thus brought into action, for the act of re-expansion takes a considerable +time, and until the tentacles are re-expanded they cannot catch prey. On the +other hand, extreme sensitiveness to slight pressure is of the highest service +to the plant; for, as we have seen, if the delicate feet of a minute struggling +insect press ever so lightly on the surfaces of two or three glands, the +tentacles bearing these glands soon curl inwards and carry the insect with them +to the centre, causing, after a time, all the circumferential tentacles to +embrace it. Nevertheless, the movements of the plant are not perfectly adapted +to its requirements; for if a bit of dry moss, peat, or other rubbish, is blown +on to the disc, as often happens, the tentacles clasp it in a useless manner. +They soon, however, discover their mistake and release such innutritious +objects. +</p> + +<p> +It is also a remarkable fact, that drops of water falling from a height, +whether under the form of natural or artificial rain, do not cause the +tentacles to move; yet the drops must strike the glands with considerable +force, more especially after the secretion has been all washed away by heavy +rain; and this often occurs, [page 36] though the secretion is so viscid that +it can be removed with difficulty merely by waving the leaves in water. If the +falling drops of water are small, they adhere to the secretion, the weight of +which must be increased in a much greater degree, as before remarked, than by +the addition of minute particles of solid matter; yet the drops never cause the +tentacles to become inflected. It would obviously have been a great evil to the +plant (as in the case of occasional touches) if the tentacles were excited to +bend by every shower of rain; but this evil has been avoided by the glands +either having become through habit insensible to the blows and prolonged +pressure of drops of water, or to their having been originally rendered +sensitive solely to the contact of solid bodies. We shall hereafter see that +the filaments on the leaves of Dionaea are likewise insensible to the impact of +fluids, though exquisitely sensitive to momentary touches from any solid body. +</p> + +<p> +When the pedicel of a tentacle is cut off by a sharp pair of scissors quite +close beneath the gland, the tentacle generally becomes inflected. I tried this +experiment repeatedly, as I was much surprised at the fact, for all other parts +of the pedicels are insensible to any stimulus. These headless tentacles after +a time re-expand; but I shall return to this subject. On the other hand, I +occasionally succeeded in crushing a gland between a pair of pincers, but this +caused no inflection. In this latter case the tentacles seem paralysed, as +likewise follows from the action of too strong solutions of certain salts, and +by too great heat, whilst weaker solutions of the same salts and a more gentle +heat cause movement. We shall also see in future chapters that various other +fluids, some [page 37] vapours, and oxygen (after the plant has been for some +time excluded from its action), all induce inflection, and this likewise +results from an induced galvanic current.* +</p> + +<p class="footnote"> +* My son Francis, guided by the observations of Dr. Burdon Sanderson on +Dionaea, finds that if two needles are inserted into the blade of a leaf of +Drosera, the tentacles do not move; but that if similar needles in connection +with the secondary coil of a Du Bois inductive apparatus are inserted, the +tentacles curve inwards in the course of a few minutes. My son hopes soon to +publish an account of his observations. [page 38] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0003" id="link2HCH0003"></a> +CHAPTER III.<br/> +AGGREGATION OF THE PROTOPLASM WITHIN THE CELLS OF THE TENTACLES.</h2> + +<p class="letter"> +Nature of the contents of the cells before aggregation—Various causes +which excite aggregation—The process commences within the glands and +travels down the tentacles— Description of the aggregated masses and of +their spontaneous movements—Currents of protoplasm along the walls of the +cells—Action of carbonate of ammonia—The granules in the protoplasm +which flows along the walls coalesce with the central masses—Minuteness +of the quantity of carbonate of ammonia causing aggregation—Action of +other salts of ammonia—Of other substances, organic fluids, +&c.—Of water—Of heat—Redissolution of the aggregated +masses—Proximate causes of the aggregation of the +protoplasm—Summary and concluding remarks—Supplementary +observations on aggregation in the roots of plants. +</p> + +<p> +I will here interrupt my account of the movements of the leaves, and describe +the phenomenon of aggregation, to which subject I have already alluded. If the +tentacles of a young, yet fully matured leaf, that has never been excited or +become inflected, be examined, the cells forming the pedicels are seen to be +filled with homogeneous, purple fluid. The walls are lined by a layer of +colourless, circulating protoplasm; but this can be seen with much greater +distinctness after the process of aggregation has been partly effected than +before. The purple fluid which exudes from a crushed tentacle is somewhat +coherent, and does not mingle with the surrounding water; it contains much +flocculent or granular matter. But this matter may have been generated by the +cells having been crushed; some degree of aggregation having been thus almost +instantly caused. [page 39] +</p> + +<p> +If a tentacle is examined some hours after the gland has been excited by +repeated touches, or by an inorganic or organic particle placed on it, or by +the absorption of certain fluids, it presents a wholly changed appearance. The +cells, instead of being filled with homogeneous purple fluid, now contain +variously shaped masses of purple matter, suspended in a colourless or almost +colourless fluid. The change is so conspicuous that it is visible through a +weak lens, and even sometimes by the naked eye; the tentacles now have a +mottled appearance, so that one thus affected can be picked out with ease from +all the others. The same result follows if the glands on the disc are irritated +in any manner, so that the exterior tentacles become inflected; for their +contents will then be found in an aggregated condition, although their glands +have not as yet touched any object. But aggregation may occur independently of +inflection, as we shall presently see. By whatever cause the process may have +been excited, it commences within the glands, and then travels down the +tentacles. It can be observed much more distinctly in the upper cells of the +pedicels than within the glands, as these are somewhat opaque. Shortly after +the tentacles have re-expanded, the little masses of protoplasm are all +redissolved, and the purple fluid within the cells becomes as homogeneous and +transparent as it was at first. The process of redissolution travels upwards +from the bases of the tentacles to the glands, and therefore in a reversed +direction to that of aggregation. Tentacles in an aggregated condition were +shown to Prof. Huxley, Dr. Hooker, and Dr. Burdon Sanderson, who observed the +changes under the microscope, and were much struck with the whole phenomenon. +[page 40] +</p> + +<p> +The little masses of aggregated matter are of the most diversified shapes, +often spherical or oval, sometimes much elongated, or quite irregular with +thread- or necklace-like or club-formed projections. They consist of thick, +apparently viscid matter, which in the exterior tentacles is of a purplish, and +in the short distal tentacles of a greenish, colour. These little masses +incessantly change their forms and positions, being never at rest. A single +mass will often separate into two, which afterwards reunite. Their movements +are rather slow, and resemble those of Amoebae or of the white corpuscles of +the blood. We +</p> + +<p> +FIG. 7. (Drosera rotundifolia.) Diagram of the same cell of a tentacle, showing +the various forms successively assumed by the aggregated masses of protoplasm. +</p> + +<p> +may, therefore, conclude that they consist of protoplasm. If their shapes are +sketched at intervals of a few minutes, they are invariably seen to have +undergone great changes of form; and the same cell has been observed for +several hours. Eight rude, though accurate sketches of the same cell, made at +intervals of between 2 m. or 3 m., are here given (fig. 7), and illustrate some +of the simpler and commonest changes. The cell A, when first sketched, included +two oval masses of purple protoplasm touching each other. These became +separate, as shown at B, and then reunited, as at C. After the next interval a +very common appearance was presented— [page 41] D, namely, the formation +of an extremely minute sphere at one end of an elongated mass. This rapidly +increased in size, as shown in E, and was then re-absorbed, as at F, by which +time another sphere had been formed at the opposite end. +</p> + +<p> +The cell above figured was from a tentacle of a dark red leaf, which had caught +a small moth, and was examined under water. As I at first thought that the +movements of the masses might be due to the absorption of water, I placed a fly +on a leaf, and when after 18 hrs. all the tentacles were well inflected, these +were examined without being immersed in water. The cell +</p> + +<p> +FIG. 8. (Drosera rotundifolia.) Diagram of the same cell of a tentacle, showing +the various forms successively assumed by the aggregated masses of protoplasm. +</p> + +<p> +here represented (fig. 8) was from this leaf, being sketched eight times in the +course of 15 m. These sketches exhibit some of the more remarkable changes +which the protoplasm undergoes. At first, there was at the base of the cell 1, +a little mass on a short footstalk, and a larger mass near the upper end, and +these seemed quite separate. Nevertheless, they may have been connected by a +fine and invisible thread of protoplasm, for on two other occasions, whilst one +mass was rapidly increasing, and another in the same cell rapidly decreasing, I +was able by varying the light and using a high power, to detect a connecting +thread of extreme tenuity, which evidently served as [page 42] the channel of +communication between the two. On the other hand, such connecting threads are +sometimes seen to break, and their extremities then quickly become club-headed. +The other sketches in fig. 8 show the forms successively assumed. +</p> + +<p> +Shortly after the purple fluid within the cells has become aggregated, the +little masses float about in a colourless or almost colourless fluid; and the +layer of white granular protoplasm which flows along the walls can now be seen +much more distinctly. The stream flows at an irregular rate, up one wall and +down the opposite one, generally at a slower rate across the narrow ends of the +elongated cells, and so round and round. But the current sometimes ceases. The +movement is often in waves, and their crests sometimes stretch almost across +the whole width of the cell, and then sink down again. Small spheres of +protoplasm, apparently quite free, are often driven by the current round the +cells; and filaments attached to the central masses are swayed to and fro, as +if struggling to escape. Altogether, one of these cells with the ever changing +central masses, and with the layer of protoplasm flowing round the walls, +presents a wonderful scene of vital activity. +</p> + +<p> +[Many observations were made on the contents of the cells whilst undergoing the +process of aggregation, but I shall detail only a few cases under different +heads. A small portion of a leaf was cut off, placed under a high power, and +the glands very gently pressed under a compressor. In 15 m. I distinctly saw +extremely minute spheres of protoplasm aggregating themselves in the purple +fluid; these rapidly increased in size, both within the cells of the glands and +of the upper ends of the pedicels. Particles of glass, cork, and cinders were +also placed on the glands of many tentacles; in 1 hr. several of them were +inflected, but after 1 hr. 35 m. there was no aggregation. Other tentacles with +these particles were examined after 8 hrs., and [page 43] now all their cells +had undergone aggregation; so had the cells of the exterior tentacles which had +become inflected through the irritation transmitted from the glands of the +disc, on which the transported particles rested. This was likewise the case +with the short tentacles round the margins of the disc, which had not as yet +become inflected. This latter fact shows that the process of aggregation is +independent of the inflection of the tentacles, of which indeed we have other +and abundant evidence. Again, the exterior tentacles on three leaves were +carefully examined, and found to contain only homogeneous purple fluid; little +bits of thread were then placed on the glands of three of them, and after 22 +hrs. the purple fluid in their cells almost down to their bases was aggregated +into innumerable, spherical, elongated, or filamentous masses of protoplasm. +The bits of thread had been carried some time previously to the central disc, +and this had caused all the other tentacles to become somewhat inflected; and +their cells had likewise undergone aggregation, which however, it should be +observed, had not as yet extended down to their bases, but was confined to the +cells close beneath the glands. +</p> + +<p> +Not only do repeated touches on the glands* and the contact of minute particles +cause aggregation, but if glands, without being themselves injured, are cut off +from the summits of the pedicels, this induces a moderate amount of aggregation +in the headless tentacles, after they have become inflected. On the other hand, +if glands are suddenly crushed between pincers, as was tried in six cases, the +tentacles seem paralysed by so great a shock, for they neither become inflected +nor exhibit any signs of aggregation. +</p> + +<p> +Carbonate of Ammonia.—Of all the causes inducing aggregation, that which, +as far as I have seen, acts the quickest, and is the most powerful, is a +solution of carbonate of ammonia. Whatever its strength may be, the glands are +always affected first, and soon become quite opaque, so as to appear black. For +instance, I placed a leaf in a few drops of a strong solution, namely, of one +part to 146 of water (or 3 grs. to 1 oz.), and observed it under a high power. +All the glands began to +</p> + +<p class="footnote"> +* Judging from an account of M. Heckel’s observations, which I have only +just seen quoted in the ‘Gardeners’ Chronicle’ (Oct. 10, +1874), he appears to have observed a similar phenomenon in the stamens of +Berberis, after they have been excited by a touch and have moved; for he says, +“the contents of each individual cell are collected together in the +centre of the cavity.” [page 44] +</p> + +<p> +darken in 10 s. (seconds); and in 13 s. were conspicuously darker. In 1 m. +extremely small spherical masses of protoplasm could be seen arising in the +cells of the pedicels close beneath the glands, as well as in the cushions on +which the long-headed marginal glands rest. In several cases the process +travelled down the pedicels for a length twice or thrice as great as that of +the glands, in about 10 m. It was interesting to observe the process +momentarily arrested at each transverse partition between two cells, and then +to see the transparent contents of the cell next below almost flashing into a +cloudy mass. In the lower part of the pedicels, the action proceeded slower, so +that it took about 20 m. before the cells halfway down the long marginal and +submarginal tentacles became aggregated. +</p> + +<p> +We may infer that the carbonate of ammonia is absorbed by the glands, not only +from its action being so rapid, but from its effect being somewhat different +from that of other salts. As the glands, when excited, secrete an acid +belonging to the acetic series, the carbonate is probably at once converted +into a salt of this series; and we shall presently see that the acetate of +ammonia causes aggregation almost or quite as energetically as does the +carbonate. If a few drops of a solution of one part of the carbonate to 437 of +water (or 1 gr. to 1 oz.) be added to the purple fluid which exudes from +crushed tentacles, or to paper stained by being rubbed with them, the fluid and +the paper are changed into a pale dirty green. Nevertheless, some purple colour +could still be detected after 1 hr. 30 m. within the glands of a leaf left in a +solution of twice the above strength (viz. 2 grs. to 1 oz.); and after 24 hrs. +the cells of the pedicels close beneath the glands still contained spheres of +protoplasm of a fine purple tint. These facts show that the ammonia had not +entered as a carbonate, for otherwise the colour would have been discharged. I +have, however, sometimes observed, especially with the long-headed tentacles on +the margins of very pale leaves immersed in a solution, that the glands as well +as the upper cells of the pedicels were discoloured; and in these cases I +presume that the unchanged carbonate had been absorbed. The appearance above +described, of the aggregating process being arrested for a short time at each +transverse partition, impresses the mind with the idea of matter passing +downwards from cell to cell. But as the cells one beneath the other undergo +aggregation when inorganic and insoluble particles are placed on the glands, +the process must be, at least in these cases, one of molecular change, +transmitted from the glands, [page 45] independently of the absorption of any +matter. So it may possibly be in the case of the carbonate of ammonia. As, +however, the aggregation caused by this salt travels down the tentacles at a +quicker rate than when insoluble particles are placed on the glands, it is +probable that ammonia in some form is absorbed not only by the glands, but +passes down the tentacles. +</p> + +<p> +Having examined a leaf in water, and found the contents of the cells +homogeneous, I placed it in a few drops of a solution of one part of the +carbonate to 437 of water, and attended to the cells immediately beneath the +glands, but did not use a very high power. No aggregation was visible in 3 m.; +but after 15 m. small spheres of protoplasm were formed, more especially +beneath the long-headed marginal glands; the process, however, in this case +took place with unusual slowness. In 25 m. conspicuous spherical masses were +present in the cells of the pedicels for a length about equal to that of the +glands; and in 3 hrs. to that of a third or half of the whole tentacle. +</p> + +<p> +If tentacles with cells containing only very pale pink fluid, and apparently +but little protoplasm, are placed in a few drops of a weak solution of one part +of the carbonate to 4375 of water (1 gr. to 10 oz.), and the highly transparent +cells beneath the glands are carefully observed under a high power, these may +be seen first to become slightly cloudy from the formation of numberless, only +just perceptible, granules, which rapidly grow larger either from coalescence +or from attracting more protoplasm from the surrounding fluid. On one occasion +I chose a singularly pale leaf, and gave it, whilst under the microscope, a +single drop of a stronger solution of one part to 437 of water; in this case +the contents of the cells did not become cloudy, but after 10 m. minute +irregular granules of protoplasm could be detected, which soon increased into +irregular masses and globules of a greenish or very pale purple tint; but these +never formed perfect spheres, though incessantly changing their shapes and +positions. +</p> + +<p> +With moderately red leaves the first effect of a solution of the carbonate +generally is the formation of two or three, or of several, extremely minute +purple spheres which rapidly increase in size. To give an idea of the rate at +which such spheres increase in size, I may mention that a rather pale purple +leaf placed under a slip of glass was given a drop of a solution of one part to +292 of water, and in 13 m. a few minute spheres of protoplasm were formed; one +of these, after 2 hrs. 30 m., was about two-thirds of the diameter of the cell. +After 4 hrs. 25 m. [page 46] it nearly equalled the cell in diameter; and a +second sphere about half as large as the first, together with a few other +minute ones, were formed. After 6 hrs. the fluid in which these spheres floated +was almost colourless. After 8 hrs. 35 m. (always reckoning from the time when +the solution was first added) four new minute spheres had appeared. Next +morning, after 22 hrs., there were, besides the two large spheres, seven +smaller ones, floating in absolutely colourless fluid, in which some flocculent +greenish matter was suspended. +</p> + +<p> +At the commencement of the process of aggregation, more especially in dark red +leaves, the contents of the cells often present a different appearance, as if +the layer of protoplasm (primordial utricle) which lines the cells had +separated itself and shrunk from the walls; an irregularly shaped purple bag +being thus formed. Other fluids, besides a solution of the carbonate, for +instance an infusion of raw meat, produce this same effect. But the appearance +of the primordial utricle shrinking from the walls is certainly false;* for +before giving the solution, I saw on several occasions that the walls were +lined with colourless flowing protoplasm, and after the bag-like masses were +formed, the protoplasm was still flowing along the walls in a conspicuous +manner, even more so than before. It appeared indeed as if the stream of +protoplasm was strengthened by the action of the carbonate, but it was +impossible to ascertain whether this was really the case. The bag-like masses, +when once formed, soon begin to glide slowly round the cells, sometimes sending +out projections which separate into little spheres; other spheres appear in the +fluid surrounding the bags, and these travel much more quickly. That the small +spheres are separate is often shown by sometimes one and then another +travelling in advance, and sometimes they revolve round each other. I have +occasionally seen spheres of this kind proceeding up and down the same side of +a cell, instead of round it. The bag-like masses after a time generally divide +into two rounded or oval masses, and these undergo the changes shown in figs. 7 +and 8. At other times spheres appear within the bags; and these coalesce and +separate in an endless cycle of change. +</p> + +<p> +After leaves have been left for several hours in a solution of the carbonate, +and complete aggregation has been effected, the +</p> + +<p class="footnote"> +* With other plants I have often seen what appears to be a true shrinking of +the primordial utricle from the walls of the cells, caused by a solution of +carbonate of ammonia, as likewise follows from mechanical injuries. [page 47] +</p> + +<p> +stream of protoplasm on the walls of the cells ceases to be visible; I observed +this fact repeatedly, but will give only one instance. A pale purple leaf was +placed in a few drops of a solution of one part to 292 of water, and in 2 hrs. +some fine purple spheres were formed in the upper cells of the pedicels, the +stream of protoplasm round their walls being still quite distinct; but after an +additional 4 hrs., during which time many more spheres were formed, the stream +was no longer distinguishable on the most careful examination; and this no +doubt was due to the contained granules having become united with the spheres, +so that nothing was left by which the movement of the limpid protoplasm could +be perceived. But minute free spheres still travelled up and down the cells, +showing that there was still a current. So it was next morning, after 22 hrs., +by which time some new minute spheres had been formed; these oscillated from +side to side and changed their positions, proving that the current had not +ceased, though no stream of protoplasm was visible. On another occasion, +however, a stream was seen flowing round the cell-walls of a vigorous, +dark-coloured leaf, after it had been left for 24 hrs. in a rather stronger +solution, namely, of one part of the carbonate to 218 of water. This leaf, +therefore, was not much or at all injured by an immersion for this length of +time in the above solution of two grains to the ounce; and on being afterwards +left for 24 hrs. in water, the aggregated masses in many of the cells were +re-dissolved, in the same manner as occurs with leaves in a state of nature +when they re-expand after having caught insects. +</p> + +<p> +In a leaf which had been left for 22 hrs. in a solution of one part of the +carbonate to 292 of water, some spheres of protoplasm (formed by the +self-division of a bag-like mass) were gently pressed beneath a covering glass, +and then examined under a high power. They were now distinctly divided by +well-defined radiating fissures, or were broken up into separate fragments with +sharp edges; and they were solid to the centre. In the larger broken spheres +the central part was more opaque, darker-coloured, and less brittle than the +exterior; the latter alone being in some cases penetrated by the fissures. In +many of the spheres the line of separation between the outer and inner parts +was tolerably well defined. The outer parts were of exactly the same very pale +purple tint, as that of the last formed smaller spheres; and these latter did +not include any darker central core. +</p> + +<p> +From these several facts we may conclude that when vigorous dark-coloured +leaves are subjected to the action of carbonate of [page 48] ammonia, the fluid +within the cells of the tentacles often aggregates exteriorly into coherent +viscid matter, forming a kind of bag. Small spheres sometimes appear within +this bag, and the whole generally soon divides into two or more spheres, which +repeatedly coalesce and redivide. After a longer or shorter time the granules +in the colourless layer of protoplasm, which flows round the walls, are drawn +to and unite with the larger spheres, or form small independent spheres; these +latter being of a much paler colour, and more brittle than the first aggregated +masses. After the granules of protoplasm have been thus attracted, the layer of +flowing protoplasm can no longer be distinguished, though a current of limpid +fluid still flows round the walls. +</p> + +<p> +If a leaf is immersed in a very strong, almost concentrated, solution of +carbonate of ammonia, the glands are instantly blackened, and they secrete +copiously; but no movement of the tentacles ensues. Two leaves thus treated +became after 1 hr. flaccid, and seemed killed; all the cells in their tentacles +contained spheres of protoplasm, but these were small and discoloured. Two +other leaves were placed in a solution not quite so strong, and there was +well-marked aggregation in 30 m. After 24 hrs. the spherical or more commonly +oblong masses of protoplasm became opaque and granular, instead of being as +usual translucent; and in the lower cells there were only innumerable minute +spherical granules. It was evident that the strength of the solution had +interfered with the completion of the process, as we shall see likewise follows +from too great heat. +</p> + +<p> +All the foregoing observations relate to the exterior tentacles, which are of a +purple colour; but the green pedicels of the short central tentacles are acted +on by the carbonate, and by an infusion of raw meat, in exactly the same +manner, with the sole difference that the aggregated masses are of a greenish +colour; so that the process is in no way dependent on the colour of the fluid +within the cells. +</p> + +<p> +Finally, the most remarkable fact with respect to this salt is the +extraordinary small amount which suffices to cause aggregation. Full details +will be given in the seventh chapter, and here it will be enough to say that +with a sensitive leaf the absorption by a gland of 1/134400 of a grain (.000482 +mgr.) is enough to cause in the course of one hour well-marked aggregation in +the cells immediately beneath the gland. +</p> + +<p> +The Effects of certain other Salts and Fluids.—Two leaves were placed in +a solution of one part of acetate of ammonia to about [page 49] 146 of water, +and were acted on quite as energetically, but perhaps not quite so quickly, as +by the carbonate. After 10 m. the glands were black, and in the cells beneath +them there were traces of aggregation, which after 15 m. was well marked, +extending down the tentacles for a length equal to that of the glands. After 2 +hrs. the contents of almost all the cells in all the tentacles were broken up +into masses of protoplasm. A leaf was immersed in a solution of one part of +oxalate of ammonia to 146 of water; and after 24 m. some, but not a +conspicuous, change could be seen within the cells beneath the glands. After 47 +m. plenty of spherical masses of protoplasm were formed, and these extended +down the tentacles for about the length of the glands. This salt, therefore, +does not act so quickly as the carbonate. With respect to the citrate of +ammonia, a leaf was placed in a little solution of the above strength, and +there was not even a trace of aggregation in the cells beneath the glands, +until 56 m. had elapsed; but it was well marked after 2 hrs. 20 m. On another +occasion a leaf was placed in a stronger solution, of one part of the citrate +to 109 of water (4 grs. to 1 oz.), and at the same time another leaf in a +solution of the carbonate of the same strength. The glands of the latter were +blackened in less than 2 m., and after 1 hr. 45 m. the aggregated masses, which +were spherical and very dark-coloured, extended down all the tentacles, for +between half and two-thirds of their lengths; whereas in the leaf immersed in +the citrate the glands, after 30 m., were of a dark red, and the aggregated +masses in the cells beneath them pink and elongated. After 1 hr. 45 m. these +masses extended down for only about one-fifth or one-fourth of the length of +the tentacles. +</p> + +<p> +Two leaves were placed, each in ten minims of a solution of one part of nitrate +of ammonia to 5250 of water (1 gr. to 12 oz.), so that each leaf received 1/576 +of a grain (.1124 mgr.). This quantity caused all the tentacles to be +inflected, but after 24 hrs. there was only a trace of aggregation. One of +these same leaves was then placed in a weak solution of the carbonate, and +after 1 hr. 45 m. the tentacles for half their lengths showed an astonishing +degree of aggregation. Two other leaves were then placed in a much stronger +solution of one part of the nitrate to 146 of water (3 grs. to 1 oz.); in one +of these there was no marked change after 3 hrs.; but in the other there was a +trace of aggregation after 52 m., and this was plainly marked after 1 hr. 22 +m., but even after 2 hrs. 12 m. there was certainly not more aggregation than +would have fol- [page 50] lowed from an immersion of from 5 m. to 10 m. in an +equally strong solution of the carbonate. +</p> + +<p> +Lastly, a leaf was placed in thirty minims of a solution of one part of +phosphate of ammonia to 43,750 of water (1 gr. to 100 oz.), so that it received +1/1600 of a grain (.04079 mgr.); this soon caused the tentacles to be strongly +inflected; and after 24 hrs. the contents of the cells were aggregated into +oval and irregularly globular masses, with a conspicuous current of protoplasm +flowing round the walls. But after so long an interval aggregation would have +ensued, whatever had caused inflection. +</p> + +<p> +Only a few other salts, besides those of ammonia, were tried in relation to the +process of aggregation. A leaf was placed in a solution of one part of chloride +of sodium to 218 of water, and after 1 hr. the contents of the cells were +aggregated into small, irregularly globular, brownish masses; these after 2 +hrs. were almost disintegrated and pulpy. It was evident that the protoplasm +had been injuriously affected; and soon afterwards some of the cells appeared +quite empty. These effects differ altogether from those produced by the several +salts of ammonia, as well as by various organic fluids, and by inorganic +particles placed on the glands. A solution of the same strength of carbonate of +soda and carbonate of potash acted in nearly the same manner as the chloride; +and here again, after 2 hrs. 30 m., the outer cells of some of the glands had +emptied themselves of their brown pulpy contents. We shall see in the eighth +chapter that solutions of several salts of soda of half the above strength +cause inflection, but do not injure the leaves. Weak solutions of sulphate of +quinine, of nicotine, camphor, poison of the cobra, &c., soon induce +well-marked aggregation; whereas certain other substances (for instance, a +solution of curare) have no such tendency. +</p> + +<p> +Many acids, though much diluted, are poisonous; and though, as will be shown in +the eighth chapter, they cause the tentacles to bend, they do not excite true +aggregation. Thus leaves were placed in a solution of one part of benzoic acid +to 437 of water; and in 15 m. the purple fluid within the cells had shrunk a +little from the walls, yet when carefully examined after 1 hr. 20 m., there was +no true aggregation; and after 24 hrs. the leaf was evidently dead. Other +leaves in iodic acid, diluted to the same degree, showed after 2 hrs. 15 m. the +same shrunken appearance of the purple fluid within the cells; and these, after +6 hrs. 15 m., were seen under a high power to be filled with excessively minute +spheres of dull reddish protoplasm, [page 51] which by the next morning, after +24 hrs., had almost disappeared, the leaf being evidently dead. Nor was there +any true aggregation in leaves immersed in propionic acid of the same strength; +but in this case the protoplasm was collected in irregular masses towards the +bases of the lower cells of the tentacles. +</p> + +<p> +A filtered infusion of raw meat induces strong aggregation, but not very +quickly. In one leaf thus immersed there was a little aggregation after 1 hr. +20 m., and in another after 1 hr. 50 m. With other leaves a considerably longer +time was required: for instance, one immersed for 5 hrs. showed no aggregation, +but was plainly acted on in 5 m.; when placed in a few drops of a solution of +one part of carbonate of ammonia to 146 of water. Some leaves were left in the +infusion for 24 hrs., and these became aggregated to a wonderful degree, so +that the inflected tentacles presented to the naked eye a plainly mottled +appearance. The little masses of purple protoplasm were generally oval or +beaded, and not nearly so often spherical as in the case of leaves subjected to +carbonate of ammonia. They underwent incessant changes of form; and the current +of colourless protoplasm round the walls was conspicuously plain after an +immersion of 25 hrs. Raw meat is too powerful a stimulant, and even small bits +generally injure, and sometimes kill, the leaves to which they are given: the +aggregated masses of protoplasm become dingy or almost colourless, and present +an unusual granular appearance, as is likewise the case with leaves which have +been immersed in a very strong solution of carbonate of ammonia. A leaf placed +in milk had the contents of its cells somewhat aggregated in 1 hr. Two other +leaves, one immersed in human saliva for 2 hrs. 30 m., and another in unboiled +white of egg for 1 hr. 30 m., were not action on in this manner; though they +undoubtedly would have been so, had more time been allowed. These same two +leaves, on being afterwards placed in a solution of carbonate of ammonia (3 +grs. to 1 oz.), had their cells aggregated, the one in 10 m. and the other in 5 +m. +</p> + +<p> +Several leaves were left for 4 hrs. 30 m. in a solution of one part of white +sugar to 146 of water, and no aggregation ensued; on being placed in a solution +of this same strength of carbonate of ammonia, they were acted on in 5 m.; as +was likewise a leaf which had been left for 1 hr. 45 m. in a moderately thick +solution of gum arabic. Several other leaves were immersed for some hours in +denser solutions of sugar, gum, and starch, and they had the contents of their +cells greatly aggregated. This [page 52] effect may be attributed to exosmose; +for the leaves in the syrup became quite flaccid, and those in the gum and +starch somewhat flaccid, with their tentacles twisted about in the most +irregular manner, the longer ones like corkscrews. We shall hereafter see that +solutions of these substances, when placed on the discs of leaves, do not +incite inflection. Particles of soft sugar were added to the secretion round +several glands and were soon dissolved, causing a great increase of the +secretion, no doubt by exosmose; and after 24 hrs. the cells showed a certain +amount of aggregation, though the tentacles were not inflected. Glycerine +causes in a few minutes well-pronounced aggregation, commencing as usual within +the glands and then travelling down the tentacles; and this I presume may be +attributed to the strong attraction of this substance for water. Immersion for +several hours in water causes some degree of aggregation. Twenty leaves were +first carefully examined, and re-examined after having been left immersed in +distilled water for various periods, with the following results. It is rare to +find even a trace of aggregation until 4 or 5 and generally not until several +more hours have elapsed. When however a leaf becomes quickly inflected in +water, as sometimes happens, especially during very warm weather, aggregation +may occur in little over 1 hr. In all cases leaves left in water for more than +24 hrs. have their glands blackened, which shows that their contents are +aggregated; and in the specimens which were carefully examined, there was +fairly well-marked aggregation in the upper cells of the pedicels. These trials +were made with cut off-leaves, and it occurred to me that this circumstance +might influence the result, as the footstalks would not perhaps absorb water +quickly enough to supply the glands as they continued to secrete. But this view +was proved erroneous, for a plant with uninjured roots, bearing four leaves, +was submerged in distilled water for 47 hrs., and the glands were blackened, +though the tentacles were very little inflected. In one of these leaves there +was only a slight degree of aggregation in the tentacles; in the second rather +more, the purple contents of the cells being a little separated from the walls; +in the third and fourth, which were pale leaves, the aggregation in the upper +parts of the pedicels was well marked. In these leaves the little masses of +protoplasm, many of which were oval, slowly changed their forms and positions; +so that a submergence for 47 hrs. had not killed the protoplasm. In a previous +trial with a submerged plant, the tentacles were not in the least inflected. +[page 53] +</p> + +<p> +Heat induces aggregation. A leaf, with the cells of the tentacles containing +only homogeneous fluid, was waved about for 1 m. in water at 130° Fahr. (54°.4 +Cent.) and was then examined under the microscope as quickly as possible, that +is in 2 m. or 3 m.; and by this time the contents of the cells had undergone +some degree of aggregation. A second leaf was waved for 2 m. in water at 125° +(51°.6 Cent.) and quickly examined as before; the tentacles were well +inflected; the purple fluid in all the cells had shrunk a little from the +walls, and contained many oval and elongated masses of protoplasm, with a few +minute spheres. A third leaf was left in water at 125°, until it cooled, and +when examined after 1 hr. 45 m., the inflected tentacles showed some +aggregation, which became after 3 hrs. more strongly marked, but did not +subsequently increase. Lastly, a leaf was waved for 1 m. in water at 120° +(48°.8 Cent.) and then left for 1 hr. 26 m. in cold water; the tentacles were +but little inflected, and there was only here and there a trace of aggregation. +In all these and other trials with warm water the protoplasm showed much less +tendency to aggregate into spherical masses than when excited by carbonate of +ammonia. +</p> + +<p> +Redissolution of the Aggregated Masses of Protoplasm.—As soon as +tentacles which have clasped an insect or any inorganic object, or have been in +any way excited, have fully re-expanded, the aggregated masses of protoplasm +are redissolved and disappear; the cells being now refilled with homogeneous +purple fluid as they were before the tentacles were inflected. The process of +redissolution in all cases commences at the bases of the tentacles, and +proceeds up them towards the glands. In old leaves, however, especially in +those which have been several times in action, the protoplasm in the uppermost +cells of the pedicels remains in a permanently more or less aggregated +condition. In order to observe the process of redissolution, the following +observations were made: a leaf was left for 24 hrs. in a little solution of one +part of carbonate of ammonia to 218 of water, and the protoplasm was as usual +aggregated into numberless purple spheres, which were incessantly changing +their forms. The leaf was then washed and placed in distilled water, and after +3 hrs. 15 m. some few of the spheres began to show by their less clearly +defined edges signs of redissolution. After 9 hrs. many of them had become +elongated, and the surrounding fluid in the cells was slightly more coloured, +showing plainly that redissolution had commenced. After 24 hrs., though many +cells still contained spheres, here and there one [page 54] could be seen +filled with purple fluid, without a vestige of aggregated protoplasm; the whole +having been redissolved. A leaf with aggregated masses, caused by its having +been waved for 2 m. in water at the temperature of 125° Fahr., was left in cold +water, and after 11 hrs. the protoplasm showed traces of incipient +redissolution. When again examined three days after its immersion in the warm +water, there was a conspicuous difference, though the protoplasm was still +somewhat aggregated. Another leaf, with the contents of all the cells strongly +aggregated from the action of a weak solution of phosphate of ammonia, was left +for between three and four days in a mixture (known to be innocuous) of one +drachm of alcohol to eight drachms of water, and when re-examined every trace +of aggregation had disappeared, the cells being now filled with homogeneous +fluid. +</p> + +<p> +We have seen that leaves immersed for some hours in dense solutions of sugar, +gum, and starch, have the contents of their cells greatly aggregated, and are +rendered more or less flaccid, with the tentacles irregularly contorted. These +leaves, after being left for four days in distilled water, became less flaccid, +with their tentacles partially re-expanded, and the aggregated masses of +protoplasm were partially redissolved. A leaf with its tentacles closely +clasped over a fly, and with the contents of the cells strongly aggregated, was +placed in a little sherry wine; after 2 hrs. several of the tentacles had +re-expanded, and the others could by a mere touch be pushed back into their +properly expanded positions, and now all traces of aggregation had disappeared, +the cells being filled with perfectly homogeneous pink fluid. The redissolution +in these cases may, I presume, be attributed to endosmose.] +</p> + +<p class="center"> +<i>On the Proximate Causes of the Process of Aggregation.</i> +</p> + +<p> +As most of the stimulants which cause the inflection of the tentacles likewise +induce aggregation in the contents of their cells, this latter process might be +thought to be the direct result of inflection; but this is not the case. If +leaves are placed in rather strong solutions of carbonate of ammonia, for +instance of three or four, and even sometimes of only two grains to the ounce +of water (i.e. one part to 109, or 146, or [page 55] 218, of water), the +tentacles are paralysed, and do not become inflected, yet they soon exhibit +strongly marked aggregation. Moreover, the short central tentacles of a leaf +which has been immersed in a weak solution of any salt of ammonia, or in any +nitrogenous organic fluid, do not become in the least inflected; nevertheless +they exhibit all the phenomena of aggregation. On the other hand, several acids +cause strongly pronounced inflection, but no aggregation. +</p> + +<p> +It is an important fact that when an organic or inorganic object is placed on +the glands of the disc, and the exterior tentacles are thus caused to bend +inwards, not only is the secretion from the glands of the latter increased in +quantity and rendered acid, but the contents of the cells of their pedicels +become aggregated. The process always commences in the glands, although these +have not as yet touched any object. Some force or influence must, therefore, be +transmitted from the central glands to the exterior tentacles, first to near +their bases causing this part to bend, and next to the glands causing them to +secrete more copiously. After a short time the glands, thus indirectly excited, +transmit or reflect some influence down their own pedicels, inducing +aggregation in cell beneath cell to their bases. +</p> + +<p> +It seems at first sight a probable view that aggregation is due to the glands +being excited to secrete more copiously, so that sufficient fluid is not left +in their cells, and in the cells of the pedicels, to hold the protoplasm in +solution. In favour of this view is the fact that aggregation follows the +inflection of the tentacles, and during the movement the glands generally, or, +as I believe, always, secrete more copiously than they did before. Again, +during the re-expansion [page 56] of the tentacles, the glands secrete less +freely, or quite cease to secrete, and the aggregated masses of protoplasm are +then redissolved. Moreover, when leaves are immersed in dense vegetable +solutions, or in glycerine, the fluid within the gland-cells passes outwards, +and there is aggregation; and when the leaves are afterwards immersed in water, +or in an innocuous fluid of less specific gravity than water, the protoplasm is +redissolved, and this, no doubt, is due to endosmose. +</p> + +<p> +Opposed to this view, that aggregation is caused by the outward passage of +fluid from the cells, are the following facts. There seems no close relation +between the degree of increased secretion and that of aggregation. Thus a +particle of sugar added to the secretion round a gland causes a much greater +increase of secretion, and much less aggregation, than does a particle of +carbonate of ammonia given in the same manner. It does not appear probable that +pure water would cause much exosmose, and yet aggregation often follows from an +immersion in water of between 16 hrs. and 24 hrs., and always after from 24 +hrs. to 48 hrs. Still less probable is it that water at a temperature of from +125° to 130° Fahr. (51°.6 to 54°.4 Cent.) should cause fluid to pass, not only +from the glands, but from all the cells of the tentacles down to their bases, +so quickly that aggregation is induced within 2 m. or 3 m. Another strong +argument against this view is, that, after complete aggregation, the spheres +and oval masses of protoplasm float about in an abundant supply of thin +colourless fluid; so that at least the latter stages of the process cannot be +due to the want of fluid to hold the protoplasm in solution. There is still +stronger evidence that aggregation is independent of secretion; for the +papillae, described in the first chapter, with which the [page 57] leaves are +studded are not glandular, and do not secrete, yet they rapidly absorb +carbonate of ammonia or an infusion of raw meat, and their contents then +quickly undergo aggregation, which afterwards spreads into the cells of the +surrounding tissues. We shall hereafter see that the purple fluid within the +sensitive filaments of Dionaea, which do not secrete, likewise undergoes +aggregation from the action of a weak solution of carbonate of ammonia. +</p> + +<p> +The process of aggregation is a vital one; by which I mean that the contents of +the cells must be alive and uninjured to be thus affected, and they must be in +an oxygenated condition for the transmission of the process at the proper rate. +Some tentacles in a drop of water were strongly pressed beneath a slip of +glass; many of the cells were ruptured, and pulpy matter of a purple colour, +with granules of all sizes and shapes, exuded, but hardly any of the cells were +completely emptied. I then added a minute drop of a solution of one part of +carbonate of ammonia to 109 of water, and after 1 hr. examined the specimens. +Here and there a few cells, both in the glands and in the pedicels, had escaped +being ruptured, and their contents were well aggregated into spheres which were +constantly changing their forms and positions, and a current could still be +seen flowing along the walls; so that the protoplasm was alive. On the other +hand, the exuded matter, which was now almost colourless instead of being +purple, did not exhibit a trace of aggregation. Nor was there a trace in the +many cells which were ruptured, but which had not been completely emptied of +their contents. Though I looked carefully, no signs of a current could be seen +within these ruptured cells. They had evidently been killed by the pressure; +and the matter which they [page 58] still contained did not undergo aggregation +any more than that which had exuded. In these specimens, as I may add, the +individuality of the life of each cell was well illustrated. +</p> + +<p> +A full account will be given in the next chapter of the effects of heat on the +leaves, and I need here only state that leaves immersed for a short time in +water at a temperature of 120° Fahr. (48°.8 Cent.), which, as we have seen, does +not immediately induce aggregation, were then placed in a few drops of a strong +solution of one part of carbonate of ammonia to 109 of water, and became finely +aggregated. On the other hand, leaves, after an immersion in water at 150° +(65°.5 Cent.), on being placed in the same strong solution, did not undergo +aggregation, the cells becoming filled with brownish, pulpy, or muddy matter. +With leaves subjected to temperatures between these two extremes of 120° and +150° Fahr. (48°.8 and 65°.5 Cent.), there were gradations in the completeness +of the process; the former temperature not preventing aggregation from the +subsequent action of carbonate of ammonia, the latter quite stopping it. Thus, +leaves immersed in water, heated to 130° (54°.4 Cent.), and then in the +solution, formed perfectly defined spheres, but these were decidedly smaller +than in ordinary cases. With other leaves heated to 140° (60° Cent.), the +spheres were extremely small, yet well defined, but many of the cells +contained, in addition, some brownish pulpy matter. In two cases of leaves +heated to 145° (62°.7 Cent.), a few tentacles could be found with some of their +cells containing a few minute spheres; whilst the other cells and other whole +tentacles included only the brownish, disintegrated or pulpy matter. +</p> + +<p> +The fluid within the cells of the tentacles must be in an oxygenated condition, +in order that the force or [page 59] influence which induces aggregation should +be transmitted at the proper rate from cell to cell. A plant, with its roots in +water, was left for 45 m. in a vessel containing 122 oz. of carbonic acid. A +leaf from this plant, and, for comparison, one from a fresh plant, were both +immersed for 1 hr. in a rather strong solution of carbonate of ammonia. They +were then compared, and certainly there was much less aggregation in the leaf +which had been subjected to the carbonic acid than in the other. Another plant +was exposed in the same vessel for 2 hrs. to carbonic acid, and one of its +leaves was then placed in a solution of one part of the carbonate to 437 of +water; the glands were instantly blackened, showing that they had absorbed, and +that their contents were aggregated; but in the cells close beneath the glands +there was no aggregation even after an interval of 3 hrs. After 4 hrs. 15 m. a +few minute spheres of protoplasm were formed in these cells, but even after 5 +hrs. 30 m. the aggregation did not extend down the pedicels for a length equal +to that of the glands. After numberless trials with fresh leaves immersed in a +solution of this strength, I have never seen the aggregating action transmitted +at nearly so slow a rate. Another plant was left for 2 hrs. in carbonic acid, +but was then exposed for 20 m. to the open air, during which time the leaves, +being of a red colour, would have absorbed some oxygen. One of them, as well as +a fresh leaf for comparison, were now immersed in the same solution as before. +The former were looked at repeatedly, and after an interval of 65 m. a few +spheres of protoplasm were first observed in the cells close beneath the +glands, but only in two or three of the longer tentacles. After 3 hrs. the +aggregation had travelled down the pedicels of a few of the tentacles [page 60] +for a length equal to that of the glands. On the other hand, in the fresh leaf +similarly treated, aggregation was plain in many of the tentacles after 15 m.; +after 65 m. it had extended down the pedicels for four, five, or more times the +lengths of the glands; and after 3 hrs. the cells of all the tentacles were +affected for one-third or one-half of their entire lengths. Hence there can be +no doubt that the exposure of leaves to carbonic acid either stops for a time +the process of aggregation, or checks the transmission of the proper influence +when the glands are subsequently excited by carbonate of ammonia; and this +substance acts more promptly and energetically than any other. It is known that +the protoplasm of plants exhibits its spontaneous movements only as long as it +is in an oxygenated condition; and so it is with the white corpuscles of the +blood, only as long as they receive oxygen from the red corpuscles;* but the +cases above given are somewhat different, as they relate to the delay in the +generation or aggregation of the masses of protoplasm by the exclusion of +oxygen. +</p> + +<p> +A Summary and Concluding Remarks.—The process of aggregation is +independent of the inflection of the tentacles and of increased secretion from +the glands. It commences within the glands, whether these have been directly +excited, or indirectly by a stimulus received from other glands. In both cases +the process is transmitted from cell to cell down the whole length of the +tentacles, being arrested for a short time at each transverse partition. With +pale-coloured leaves the first change which is perceptible, but only +</p> + +<p class="footnote"> +* With respect to plants, Sachs, ‘Traité de Bot.’ 3rd edit., 1874, +p. 864. On blood corpuscles, see ‘Quarterly Journal of Microscopical +Science,’ April 1874, p. 185.’ [page 61] +</p> + +<p> +under a high power, is the appearance of the finest granules in the fluid +within the cells, making it slightly cloudy. These granules soon aggregate into +small globular masses. I have seen a cloud of this kind appear in 10 s. after a +drop of a solution of carbonate of ammonia had been given to a gland. With dark +red leaves the first visible change often is the conversion of the outer layer +of the fluid within the cells into bag-like masses. The aggregated masses, +however they may have been developed, incessantly change their forms and +positions. They are not filled with fluid, but are solid to their centres. +Ultimately the colourless granules in the protoplasm which flows round the +walls coalesce with the central spheres or masses; but there is still a current +of limpid fluid flowing within the cells. As soon as the tentacles fully +re-expand, the aggregated masses are redissolved, and the cells become filled +with homogeneous purple fluid, as they were at first. The process of +redissolution commences at the bases of the tentacles, thence proceeding +upwards to the glands; and, therefore, in a reversed direction to that of +aggregation. +</p> + +<p> +Aggregation is excited by the most diversified causes,—by the glands +being several times touched,—by the pressure of particles of any kind, +and as these are supported by the dense secretion, they can hardly press on the +glands with the weight of a millionth of a grain,*—by the tentacles being +cut off close beneath +</p> + +<p class="footnote"> +* According to Hofmeister (as quoted by Sachs, ‘Traité de Bot.’ +1874, p. 958), very slight pressure on the cell-membrane arrests immediately +the movements of the protoplasm, and even determines its separation from the +walls. But the process of aggregation is a different phenomenon, as it relates +to the contents of the cells, and only secondarily to the layer of protoplasm +which flows along the walls; though no doubt the effects of pressure or of a +touch on the outside must be transmitted through this layer. [page 62] +</p> + +<p> +the glands,—by the glands absorbing various fluids or matter dissolved +out of certain bodies,—by exosmose,—and by a certain degree of +heat. On the other hand, a temperature of about 150° Fahr. (65°.5 Cent.) does +not excite aggregation; nor does the sudden crushing of a gland. If a cell is +ruptured, neither the exuded matter nor that which still remains within the +cell undergoes aggregation when carbonate of ammonia is added. A very strong +solution of this salt and rather large bits of raw meat prevent the aggregated +masses being well developed. From these facts we may conclude that the +protoplasmic fluid within a cell does not become aggregated unless it be in a +living state, and only imperfectly if the cell has been injured. We have also +seen that the fluid must be in an oxygenated state, in order that the process +of aggregation should travel from cell to cell at the proper rate. +</p> + +<p> +Various nitrogenous organic fluids and salts of ammonia induce aggregation, but +in different degrees and at very different rates. Carbonate of ammonia is the +most powerful of all known substances; the absorption of 1/134400 of a grain +(.000482 mg.) by a gland suffices to cause all the cells of the same tentacle +to become aggregated. The first effect of the carbonate and of certain other +salts of ammonia, as well as of some other fluids, is the darkening or +blackening of the glands. This follows even from long immersion in cold +distilled water. It apparently depends in chief part on the strong aggregation +of their cell-contents, which thus become opaque, and do not reflect light. +Some other fluids render the glands of a brighter red; whilst certain acids, +though much diluted, the poison of the cobra-snake, &c., make the glands +perfectly white and opaque; and this seems to depend on the coagulation of +their contents without [page 63] any aggregation. Nevertheless, before being +thus affected, they are able, at least in some cases, to excite aggregation in +their own tentacles. +</p> + +<p> +That the central glands, if irritated, send centrifugally some influence to the +exterior glands, causing them to send back a centripetal influence inducing +aggregation, is perhaps the most interesting fact given in this chapter. But +the whole process of aggregation is in itself a striking phenomenon. Whenever +the peripheral extremity of a nerve is touched or pressed, and a sensation is +felt, it is believed that an invisible molecular change is sent from one end of +the nerve to the other; but when a gland of Drosera is repeatedly touched or +gently pressed, we can actually see a molecular change proceeding from the +gland down the tentacle; though this change is probably of a very different +nature from that in a nerve. Finally, as so many and such widely different +causes excite aggregation, it would appear that the living matter within the +gland-cells is in so unstable a condition that almost any disturbance suffices +to change its molecular nature, as in the case of certain chemical compounds. +And this change in the glands, whether excited directly, or indirectly by a +stimulus received from other glands, is transmitted from cell to cell, causing +granules of protoplasm either to be actually generated in the previously limpid +fluid or to coalesce and thus to become visible. +</p> + +<p> +Supplementary Observations on the Process of Aggregation in the Roots of +Plants. +</p> + +<p> +It will hereafter be seen that a weak solution of the carbonate of ammonia +induces aggregation in the cells of the roots of Drosera; and this led me to +make a few trials on the roots of other plants. I dug up in the latter part of +October the first weed which I met with, viz. Euphorbia peplus, being care- +[page 64] ful not to injure the roots; these were washed and placed in a little +solution of one part of carbonate of ammonia to 146 of water. In less than one +minute I saw a cloud travelling from cell to cell up the roots, with wonderful +rapidity. After from 8 m. to 9 m. the fine granules, which caused this cloudy +appearance, became aggregated towards the extremities of the roots into +quadrangular masses of brown matter; and some of these soon changed their forms +and became spherical. Some of the cells, however, remained unaffected. I +repeated the experiment with another plant of the same species, but before I +could get the specimen into focus under the microscope, clouds of granules and +quadrangular masses of reddish and brown matter were formed, and had run far up +all the roots. A fresh root was now left for 18 hrs. in a drachm of a solution +of one part of the carbonate to 437 of water, so that it received 1/8 of a +grain, or 2.024 mg. When examined, the cells of all the roots throughout their +whole length contained aggregated masses of reddish and brown matter. Before +making these experiments, several roots were closely examined, and not a trace +of the cloudy appearance or of the granular masses could be seen in any of +them. Roots were also immersed for 35 m. in a solution of one part of carbonate +of potash to 218 of water; but this salt produced no effect. +</p> + +<p> +I may here add that thin slices of the stem of the Euphorbia were placed in the +same solution, and the cells which were green instantly became cloudy, whilst +others which were before colourless were clouded with brown, owing to the +formation of numerous granules of this tint. I have also seen with various +kinds of leaves, left for some time in a solution of carbonate of ammonia, that +the grains of chlorophyll ran together and partially coalesced; and this seems +to be a form of aggregation. +</p> + +<p> +Plants of duck-weed (Lemna) were left for between 30 m. and 45 m. in a solution +of one part of this same salt to 146 of water, and three of their roots were +then examined. In two of them, all the cells which had previously contained +only limpid fluid now included little green spheres. After from 1 1/2 hr. to 2 +hrs. similar spheres appeared in the cells on the borders of the leaves; but +whether the ammonia had travelled up the roots or had been directly absorbed by +the leaves, I cannot say. As one species, Lemna arrhiza, produces no roots, the +latter alternative is perhaps the most probable. After about 2 1/2 hrs. some of +the little green spheres in the roots were broken up into small granules which +exhibited Brownian movements. Some duck-weed was also left for 1 hr. 30 m. in a +solution of one part of [page 65] carbonate of potash to 218 of water, and no +decided change could be perceived in the cells of the roots; but when these +same roots were placed for 25 m. in a solution of carbonate of ammonia of the +same strength, little green spheres were formed. +</p> + +<p> +A green marine alga was left for some time in this same solution, but was very +doubtfully affected. On the other hand, a red marine alga, with finely pinnated +fronds, was strongly affected. The contents of the cells aggregated themselves +into broken rings, still of a red colour, which very slowly and slightly +changed their shapes, and the central spaces within these rings became cloudy +with red granular matter. The facts here given (whether they are new, I know +not) indicate that interesting results would perhaps be gained by observing the +action of various saline solutions and other fluids on the roots of plants. +[page 66] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0004" id="link2HCH0004"></a> +CHAPTER IV.<br/> +THE EFFECTS OF HEAT ON THE LEAVES.</h2> + +<p class="letter"> +Nature of the experiments—Effects of boiling water—Warm water +causes rapid inflection—Water at a higher temperature does not cause +immediate inflection, but does not kill the leaves, as shown by their +subsequent re-expansion and by the aggregation of the protoplasm—A still +higher temperature kills the leaves and coagulates the albuminous contents of +the glands. +</p> + +<p> +In my observations on Drosera rotundifolia, the leaves seemed to be more +quickly inflected over animal substances, and to remain inflected for a longer +period during very warm than during cold weather. I wished, therefore, to +ascertain whether heat alone would induce inflection, and what temperature was +the most efficient. Another interesting point presented itself, namely, at what +degree life was extinguished; for Drosera offers unusual facilities in this +respect, not in the loss of the power of inflection, but in that of subsequent +re-expansion, and more especially in the failure of the protoplasm to become +aggregated, when the leaves after being heated are immersed in a solution of +carbonate of ammonia.* +</p> + +<p class="footnote"> +* When my experiments on the effects of heat were made, I was not aware that +the subject had been carefully investigated by several observers. For instance, +Sachs is convinced (‘Traité de Botanique,’ 1874, pp. 772, 854) that +the most different kinds of plants all perish if kept for 10 m. in water at 45° +to 46° Cent., or 113° to 115° Fahr.; and he concludes that the protoplasm +within their cells always coagulates, if in a damp condition, at a temperature +of between 50° and 60° Cent., or 122° to 140° Fahr. Max Schultze and Kühne (as +quoted by Dr. Bastian in ‘Contemp. Review,’ 1874, p. 528) +“found that the protoplasm of plant-cells, with which they experimented, +was always killed and [[page 67]] altered by a very brief exposure to a +temperature of 118 1/2° Fahr. as a maximum.” As my results are deduced +from special phenomena, namely, the subsequent aggregation of the protoplasm +and the re-expansion of the tentacles, they seem to me worth giving. We shall +find that Drosera resists heat somewhat better than most other plants. That +there should be considerable differences in this respect is not surprising, +considering that some low vegetable organisms grow in hot springs—cases +of which have been collected by Prof. Wyman (‘American Journal of +Science,’ vol. xliv. 1867). Thus, Dr. Hooker found Confervae in water at +168° Fahr.; Humboldt, at 185° Fahr.; and Descloizeaux, at 208° Fahr.) [page 67] +</p> + +<p> +[My experiments were tried in the following manner. Leaves were cut off, and +this does not in the least interfere with their powers; for instance, three cut +off leaves, with bits of meat placed on them, were kept in a damp atmosphere, +and after 23 hrs. closely embraced the meat both with their tentacles and +blades; and the protoplasm within their cells was well aggregated. Three ounces +of doubly distilled water was heated in a porcelain vessel, with a delicate +thermometer having a long bulb obliquely suspended in it. The water was +gradually raised to the required temperature by a spirit-lamp moved about under +the vessel; and in all cases the leaves were continually waved for some minutes +close to the bulb. They were then placed in cold water, or in a solution of +carbonate of ammonia. In other cases they were left in the water, which had +been raised to a certain temperature, until it cooled. Again in other cases the +leaves were suddenly plunged into water of a certain temperature, and kept +there for a specified time. Considering that the tentacles are extremely +delicate, and that their coats are very thin, it seems scarcely possible that +the fluid contents of their cells should not have been heated to within a +degree or two of the temperature of the surrounding water. Any further +precautions would, I think, have been superfluous, as the leaves from age or +constitutional causes differ slightly in their sensitiveness to heat. +</p> + +<p> +It will be convenient first briefly to describe the effects of immersion for +thirty seconds in boiling water. The leaves are rendered flaccid, with their +tentacles bowed backwards, which, as we shall see in a future chapter, is +probably due to their outer surfaces retaining their elasticity for a longer +period than their inner surfaces retain the power of contraction. The purple +fluid within the cells of the pedicels is rendered finely granular, but there +is no true aggregation; nor does this follow [page 68] when the leaves are +subsequently placed in a solution of carbonate of ammonia. But the most +remarkable change is that the glands become opaque and uniformly white; and +this may be attributed to the coagulation of their albuminous contents. +</p> + +<p> +My first and preliminary experiment consisted in putting seven leaves in the +same vessel of water, and warming it slowly up to the temperature of 110° Fahr. +(43°.3 Cent.); a leaf being taken out as soon as the temperature rose to 80° +(26°.6 Cent.), another at 85°, another at 90°, and so on. Each leaf, when taken +out, was placed in water at the temperature of my room, and the tentacles of +all soon became slightly, though irregularly, inflected. They were now removed +from the cold water and kept in damp air, with bits of meat placed on their +discs. The leaf which had been exposed to the temperature of 110o became in 15 +m. greatly inflected; and in 2 hrs. every single tentacle closely embraced the +meat. So it was, but after rather longer intervals, with the six other leaves. +It appears, therefore, that the warm bath had increased their sensitiveness +when excited by meat. +</p> + +<p> +I next observed the degree of inflection which leaves underwent within stated +periods, whilst still immersed in warm water, kept as nearly as possible at the +same temperature; but I will here and elsewhere give only a few of the many +trials made. A leaf was left for 10 m. in water at 100° (37°.7 Cent.), but no +inflection occurred. A second leaf, however, treated in the same manner, had a +few of its exterior tentacles very slightly inflected in 6 m., and several +irregularly but not closely inflected in 10 m. A third leaf, kept in water at +105° to 106° (40°.5 to 41°.1 Cent.), was very moderately inflected in 6 m. A +fourth leaf, in water at 110° (43°.3 Cent.), was somewhat inflected in 4 m., +and considerably so in from 6 to 7 m. +</p> + +<p> +Three leaves were placed in water which was heated rather quickly, and by the +time the temperature rose to 115°-116° (46°.1 to 46°.06 Cent.), all three were +inflected. I then removed the lamp, and in a few minutes every single tentacle +was closely inflected. The protoplasm within the cells was not killed, for it +was seen to be in distinct movement; and the leaves, having been left in cold +water for 20 hrs., re-expanded. Another leaf was immersed in water at 100o +(37.7° Cent.), which was raised to 120° (48°.8 Cent.); and all the tentacles, +except the extreme marginal ones, soon became closely inflected. The leaf was +now placed in cold water, and in 7 hrs. 30 m. it had partly, and in 10 hrs. +fully, re-expanded. On the following morning it was immersed in a weak solution +of carbonate of [page 69] ammonia, and the glands quickly became black, with +strongly marked aggregation in the tentacles, showing that the protoplasm was +alive, and that the glands had not lost their power of absorption. Another leaf +was placed in water at 110o (43°.3 Cent.) which was raised to 120° (48°.8 +Cent.); and every tentacle, excepting one, was quickly and closely inflected. +This leaf was now immersed in a few drops of a strong solution of carbonate of +ammonia (one part to 109 of water); in 10 m. all the glands became intensely +black, and in 2 hrs. the protoplasm in the cells of the pedicels was well +aggregated. Another leaf was suddenly plunged, and as usual waved about, in +water at 120°, and the tentacles became inflected in from 2 m. to 3 m., but +only so as to stand at right angles to the disc. The leaf was now placed in the +same solution (viz. one part of carbonate of ammonia to 109 of water, or 4 grs. +to 1 oz., which I will for the future designate as the strong solution), and +when I looked at it again after the interval of an hour, the glands were +blackened, and there was well-marked aggregation. After an additional interval +of 4 hrs. the tentacles had become much more inflected. It deserves notice that +a solution as strong as this never causes inflection in ordinary cases. Lastly +a leaf was suddenly placed in water at 125° (51°.6 Cent.), and was left in it +until the water cooled; the tentacles were rendered of a bright red and soon +became inflected. The contents of the cells underwent some degree of +aggregation, which in the course of three hours increased; but the masses of +protoplasm did not become spherical, as almost always occurs with leaves +immersed in a solution of carbonate of ammonia.] +</p> + +<p> +We learn from these cases that a temperature of from 120° to 125° (48°.8 to +51°.6 Cent.) excites the tentacles into quick movement, but does not kill the +leaves, as shown either by their subsequent re-expansion or by the aggregation +of the protoplasm. We shall now see that a temperature of 130° (54°.4 Cent.) is +too high to cause immediate inflection, yet does not kill the leaves. +</p> + +<p> +[Experiment 1.—A leaf was plunged, and as in all cases waved about for a +few minutes, in water at 130° (54°.4 Cent.), but there was no trace of +inflection; it was then placed in cold water, and after an interval of 15 m. +very slow movement was [page 70] distinctly seen in a small mass of protoplasm +in one of the cells of a tentacle.* After a few hours all the tentacles and the +blade became inflected. +</p> + +<p> +Experiment 2.—Another leaf was plunged into water at 130o to 131o, and as +before there was no inflection. After being kept in cold water for an hour, it +was placed in the strong solution of ammonia, and in the course of 55 m. the +tentacles were considerably inflected. The glands, which before had been +rendered of a brighter red, were now blackened. The protoplasm in the cells of +the tentacles was distinctly aggregated; but the spheres were much smaller than +those generated in unheated leaves when subjected to carbonate of ammonia. +After an additional 2 hrs. all the tentacles, excepting six or seven, were +closely inflected. +</p> + +<p> +Experiment 3.—A similar experiment to the last, with exactly the same +results. +</p> + +<p> +Experiment 4.—A fine leaf was placed in water at 100° (37°.7 Cent.), +which was then raised to 145° (62°.7 Cent.). Soon after immersion, there was, +as might have been expected, strong inflection. The leaf was now removed and +left in cold water; but from having been exposed to so high a temperature, it +never re-expanded. +</p> + +<p> +Experiment 5.—Leaf immersed at 130° (54°.4 Cent.), and the water raised +to 145° (62°.7 Cent.), there was no immediate inflection; it was then placed in +cold water, and after 1 hr. 20 m. some of the tentacles on one side became +inflected. This leaf was now placed in the strong solution, and in 40 m. all +the submarginal tentacles were well inflected, and the glands blackened. After +an additional interval of 2 hrs. 45 m. all the tentacles, except eight or ten, +were closely inflected, with their cells exhibiting a slight degree of +aggregation; but the spheres of protoplasm were very small, and the cells of +the exterior tentacles contained some pulpy or disintegrated brownish matter. +</p> + +<p> +Experiments 6 and 7.—Two leaves were plunged in water at 135° (57°.2 +Cent.) which was raised to 145° (62°.7 Cent.); neither became inflected. One of +these, however, after having been left for 31 m. in cold water, exhibited some +slight inflection, which increased after an additional interval of 1 hr. 45 m., +until +</p> + +<p class="footnote"> +* Sachs states (‘Traité de Botanique,’ 1874, p. 855) that the +movements of the protoplasm in the hairs of a Cucurbita ceased after they were +exposed for 1 m. in water to a temperature of 47° to 48° Cent., or 117° to 119° +Fahr. [page 71] +</p> + +<p> +all the tentacles, except sixteen or seventeen, were more or less inflected; +but the leaf was so much injured that it never re-expanded. The other leaf, +after having been left for half an hour in cold water, was put into the strong +solution, but no inflection ensued; the glands, however, were blackened, and in +some cells there was a little aggregation, the spheres of protoplasm being +extremely small; in other cells, especially in the exterior tentacles, there +was much greenish-brown pulpy matter. +</p> + +<p> +Experiment 8.—A leaf was plunged and waved about for a few minutes in +water at 140° (60° Cent.), and was then left for half an hour in cold water, but +there was no inflection. It was now placed in the strong solution, and after 2 +hrs. 30 m. the inner submarginal tentacles were well inflected, with their +glands blackened, and some imperfect aggregation in the cells of the pedicels. +Three or four of the glands were spotted with the white porcelain-like +structure, like that produced by boiling water. I have seen this result in no +other instance after an immersion of only a few minutes in water at so low a +temperature as 140°, and in only one leaf out of four, after a similar +immersion at a temperature of 145° Fahr. On the other hand, with two leaves, +one placed in water at 145° (62°.7 Cent.), and the other in water at 140° +(60° Cent.), both being left therein until the water cooled, the glands of both +became white and porcelain-like. So that the duration of the immersion is an +important element in the result. +</p> + +<p> +Experiment 9.—A leaf was placed in water at 140° (60° Cent.), which was +raised to 150° (65°.5 Cent.); there was no inflection; on the contrary, the +outer tentacles were somewhat bowed backwards. The glands became like +porcelain, but some of them were a little mottled with purple. The bases of the +glands were often more affected than their summits. This leaf having been left +in the strong solution did not undergo any inflection or aggregation. +</p> + +<p> +Experiment 10.—A leaf was plunged in water at 150° to 150 1/2° (65°.5 +Cent.); it became somewhat flaccid, with the outer tentacles slightly reflexed, +and the inner ones a little bent inwards, but only towards their tips; and this +latter fact shows that the movement was not one of true inflection, as the +basal part alone normally bends. The tentacles were as usual rendered of a very +bright red, with the glands almost white like porcelain, yet tinged with pink. +The leaf having been placed in the strong solution, the cell-contents of the +tentacles became of a muddy-brown, with no trace of aggregation. [page 72] +</p> + +<p> +Experiment 11.—A leaf was immersed in water at 145° (62°.7 Cent.), which +was raised to 156° (68°.8 Cent.). The tentacles became bright red and somewhat +reflexed, with almost all the glands like porcelain; those on the disc being +still pinkish, those near the margin quite white. The leaf being placed as +usual first in cold water and then in the strong solution, the cells in the +tentacles became of a muddy greenish brown, with the protoplasm not aggregated. +Nevertheless, four of the glands escaped being rendered like porcelain, and the +pedicels of these glands were spirally curled, like a French horn, towards +their upper ends; but this can by no means be considered as a case of true +inflection. The protoplasm within the cells of the twisted portions was +aggregated into distinct though excessively minute purple spheres. This case +shows clearly that the protoplasm, after having been exposed to a high +temperature for a few minutes, is capable of aggregation when afterwards +subjected to the action of carbonate of ammonia, unless the heat has been +sufficient to cause coagulation.] +</p> + +<p> +Concluding Remarks.—As the hair-like tentacles are extremely thin and +have delicate walls, and as the leaves were waved about for some minutes close +to the bulb of the thermometer, it seems scarcely possible that they should not +have been raised very nearly to the temperature which the instrument indicated. +From the eleven last observations we see that a temperature of 130° (54°.4 +Cent.) never causes the immediate inflection of the tentacles, though a +temperature from 120° to 125° (48°.8 to 51°.6 Cent.) quickly produces this +effect. But the leaves are paralysed only for a time by a temperature of 130°, +as afterwards, whether left in simple water or in a solution of carbonate of +ammonia, they become inflected and their protoplasm undergoes aggregation. This +great difference in the effects of a higher and lower temperature may be +compared with that from immersion in strong and weak solutions of the salts of +ammonia; for the former do not excite movement, whereas the latter act +energetically. A temporary suspension of the [page 73] power of movement due to +heat is called by Sachs* heat-rigidity; and this in the case of the +sensitive-plant (Mimosa) is induced by its exposure for a few minutes to humid +air, raised to 120°-122° Fahr., or 49° to 50° Cent. It deserves notice that the +leaves of Drosera, after being immersed in water at 130° Fahr., are excited +into movement by a solution of the carbonate so strong that it would paralyse +ordinary leaves and cause no inflection. +</p> + +<p> +The exposure of the leaves for a few minutes even to a temperature of 145° +Fahr. (62°.7 Cent.) does not always kill them; as when afterwards left in cold +water, or in a strong solution of carbonate of ammonia, they generally, though +not always, become inflected; and the protoplasm within their cells undergoes +aggregation, though the spheres thus formed are extremely small, with many of +the cells partly filled with brownish muddy matter. In two instances, when +leaves were immersed in water, at a lower temperature than 130° (54°.4 Cent.), +which was then raised to 145° (62°.7 Cent.), they became during the earlier +period of immersion inflected, but on being afterwards left in cold water were +incapable of re-expansion. Exposure for a few minutes to a temperature of 145o +sometimes causes some few of the more sensitive glands to be speckled with the +porcelain-like appearance; and on one occasion this occurred at a temperature +of 140° (60° Cent.). On another occasion, when a leaf was placed in water at +this temperature of only 140o, and left therein till the water cooled, every +gland became like porcelain. Exposure for a few minutes to a temperature of +150° (65°.5 Cent.) generally produces this effect, yet many glands retain a +</p> + +<p class="footnote"> +* ‘Traité de Bot.’ 1874, p. 1034. [page 74] +</p> + +<p> +pinkish colour, and many present a speckled appearance. This high temperature +never causes true inflection; on the contrary, the tentacles commonly become +reflexed, though to a less degree than when immersed in boiling water; and this +apparently is due to their passive power of elasticity. After exposure to a +temperature of 150° Fahr., the protoplasm, if subsequently subjected to +carbonate of ammonia, instead of undergoing aggregation, is converted into +disintegrated or pulpy discoloured matter. In short, the leaves are generally +killed by this degree of heat; but owing to differences of age or constitution, +they vary somewhat in this respect. In one anomalous case, four out of the many +glands on a leaf, which had been immersed in water raised to 156° (68°.8 +Cent.), escaped being rendered porcellanous;* and the protoplasm in the cells +close beneath these glands underwent some slight, though imperfect, degree of +aggregation. +</p> + +<p> +Finally, it is a remarkable fact that the leaves of Drosera rotundifolia, which +flourishes on bleak upland moors throughout Great Britain, and exists (Hooker) +within the Arctic Circle, should be able to withstand for even a short time +immersion in water heated to a temperature of 145°.** +</p> + +<p> +It may be worth adding that immersion in cold +</p> + +<p class="footnote"> +* As the opacity and porcelain-like appearance of the glands is probably due to +the coagulation of the albumen, I may add, on the authority of Dr. Burdon +Sanderson, that albumen coagulates at about 155o, but, in presence of acids, +the temperature of coagulation is lower. The leaves of Drosera contain an acid, +and perhaps a difference in the amount contained may account for the slight +differences in the results above recorded. +</p> + +<p class="footnote"> +** It appears that cold-blooded animals are, as might have been expected, far +more sensitive to an increase of temperature than is Drosera. Thus, as I hear +from Dr. Burdon Sanderson, a frog begins to be distressed in water at a +temperature of only 85° Fahr. At 95° the muscles become rigid, and the animal +dies in a stiffened condition. [page 75] +</p> + +<p> +water does not cause any inflection: I suddenly placed four leaves, taken from +plants which had been kept for several days at a high temperature, generally +about 75° Fahr. (23°.8 Cent.), in water at 45° (7°.2 Cent.), but they were +hardly at all affected; not so much as some other leaves from the same plants, +which were at the same time immersed in water at 75°; for these became in a +slight degree inflected. [page 76] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0005" id="link2HCH0005"></a> +CHAPTER V.<br/> +THE EFFECTS OF NON-NITROGENOUS AND NITROGENOUS ORGANIC FLUIDS ON THE +LEAVES.</h2> + +<p class="letter"> +Non-nitrogenous fluids—Solutions of gum +arabic—Sugar—Starch—Diluted alcohol—Olive oil— +Infusion and decoction of tea—Nitrogenous +fluids—Milk—Urine—Liquid albumen—Infusion of raw +meat—Impure mucus—Saliva—Solution of +isinglass—Difference in the action of these two sets of +fluids—Decoction of green peas—Decoction and infusion of +cabbage—Decoction of grass leaves. +</p> + +<p> +When, in 1860, I first observed Drosera, and was led to believe that the leaves +absorbed nutritious matter from the insects which they captured, it seemed to +me a good plan to make some preliminary trials with a few common fluids, +containing and not containing nitrogenous matter; and the results are worth +giving. +</p> + +<p> +In all the following cases a drop was allowed to fall from the same pointed +instrument on the centre of the leaf; and by repeated trials one of these drops +was ascertained to be on an average very nearly half a minim, or 1/960 of a +fluid ounce, or .0295 ml. But these measurements obviously do not pretend to +any strict accuracy; moreover, the drops of the viscid fluids were plainly +larger than those of water. Only one leaf on the same plant was tried, and the +plants were collected from two distant localities. The experiments were made +during August and September. In judging of the effects, one caution is +necessary: if a drop of any adhesive fluid is placed on an old or feeble leaf, +the glands of which have ceased to secrete copiously, the drop sometimes dries +up, especially if the plant [page 77] is kept in a room, and some of the +central and submarginal tentacles are thus drawn together, giving to them the +false appearance of having become inflected. This sometimes occurs with water, +as it is rendered adhesive by mingling with the viscid secretion. Hence the +only safe criterion, and to this alone I have trusted, is the bending inwards +of the exterior tentacles, which have not been touched by the fluid, or at most +only at their bases. In this case the movement is wholly due to the central +glands having been stimulated by the fluid, and transmitting a motor impulse to +the exterior tentacles. The blade of the leaf likewise often curves inwards, in +the same manner as when an insect or bit of meat is placed on the disc. This +latter movement is never caused, as far as I have seen, by the mere drying up +of an adhesive fluid and the consequent drawing together of the tentacles. +</p> + +<p> +First for the non-nitrogenous fluids. As a preliminary trial, drops of +distilled water were placed on between thirty and forty leaves, and no effect +whatever was produced; nevertheless, in some other and rare cases, a few +tentacles became for a short time inflected; but this may have been caused by +the glands having been accidentally touched in getting the leaves into a proper +position. That water should produce no effect might have been anticipated, as +otherwise the leaves would have been excited into movement by every shower of +rain. +</p> + +<p> +[Gum arabic.—Solutions of four degrees of strength were made; one of six +grains to the ounce of water (one part to 73); a second rather stronger, yet +very thin; a third moderately thick, and a fourth so thick that it would only +just drop from a pointed instrument. These were tried on fourteen leaves; the +drops being left on the discs from 24 hrs. to 44 hrs.; generally about [page +78] 30 hrs. Inflection was never thus caused. It is necessary to try pure gum +arabic, for a friend tried a solution bought ready prepared, and this caused +the tentacles to bend; but he afterwards ascertained that it contained much +animal matter, probably glue. +</p> + +<p> +Sugar.—Drops of a solution of white sugar of three strengths (the weakest +containing one part of sugar to 73 of water) were left on fourteen leaves from +32 hrs. to 48 hrs.; but no effect was produced. +</p> + +<p> +Starch.—A mixture about as thick as cream was dropped on six leaves and +left on them for 30 hrs., no effect being produced. I am surprised at this +fact, as I believe that the starch of commerce generally contains a trace of +gluten, and this nitrogenous substance causes inflection, as we shall see in +the next chapter. +</p> + +<p> +Alcohol, Diluted.—One part of alcohol was added to seven of water, and +the usual drops were placed on the discs of three leaves. No inflection ensued +in the course of 48 hrs. To ascertain whether these leaves had been at all +injured, bits of meat were placed on them, and after 24 hrs. they were closely +inflected. I also put drops of sherry-wine on three other leaves; no inflection +was caused, though two of them seemed somewhat injured. We shall hereafter see +that cut off leaves immersed in diluted alcohol of the above strength do not +become inflected. +</p> + +<p> +Olive Oil.—drops were placed on the discs of eleven leaves, and no effect +was produced in from 24 hrs. to 48 hrs. Four of these leaves were then tested +by bits of meat on their discs, and three of them were found after 24 hrs. with +all their tentacles and blades closely inflected, whilst the fourth had only a +few tentacles inflected. It will, however, be shown in a future place, that cut +off leaves immersed in olive oil are powerfully affected. +</p> + +<p> +Infusion and Decoction of Tea.—Drops of a strong infusion and decoction, +as well as of a rather weak decoction, of tea were placed on ten leaves, none +of which became inflected. I afterwards tested three of them by adding bits of +meat to the drops which still remained on their discs, and when I examined them +after 24 hrs. they were closely inflected. The chemical principle of tea, +namely theine, was subsequently tried and produced no effect. The albuminous +matter which the leaves must originally have contained, no doubt, had been +rendered insoluble by their having been completely dried.] +</p> + +<p> +We thus see that, excluding the experiments with water, sixty-one leaves were +tried with drops of the [page 79] above-named non-nitrogenous fluids; and the +tentacles were not in a single case inflected. +</p> + +<p> +[With respect to nitrogenous fluids, the first which came to hand were tried. +The experiments were made at the same time and in exactly the same manner as +the foregoing. As it was immediately evident that these fluids produced a great +effect, I neglected in most cases to record how soon the tentacles became +inflected. But this always occurred in less than 24 hrs.; whilst the drops of +non-nitrogenous fluids which produced no effect were observed in every case +during a considerably longer period. +</p> + +<p> +Milk.—Drops were placed on sixteen leaves, and the tentacles of all, as +well as the blades of several, soon became greatly inflected. The periods were +recorded in only three cases, namely, with leaves on which unusually small +drops had been placed. Their tentacles were somewhat inflected in 45 m.; and +after 7 hrs. 45 m. the blades of two were so much curved inwards that they +formed little cups enclosing the drops. These leaves re-expanded on the third +day. On another occasion the blade of a leaf was much inflected in 5 hrs. after +a drop of milk had been placed on it. +</p> + +<p> +Human Urine.—Drops were placed on twelve leaves, and the tentacles of +all, with a single exception, became greatly inflected. Owing, I presume, to +differences in the chemical nature of the urine on different occasions, the +time required for the movements of the tentacles varied much, but was always +effected in under 24 hrs. In two instances I recorded that all the exterior +tentacles were completely inflected in 17 hrs., but not the blade of the leaf. +In another case the edges of a leaf, after 25 hrs. 30 m., became so strongly +inflected that it was converted into a cup. The power of urine does not lie in +the urea, which, as we shall hereafter see, is inoperative. +</p> + +<p> +Albumen (fresh from a hen’s egg), placed on seven leaves, caused the +tentacles of six of them to be well inflected. In one case the edge of the leaf +itself became much curled in after 20 hrs. The one leaf which was unaffected +remained so for 26 hrs., and was then treated with a drop of milk, and this +caused the tentacles to bend inwards in 12 hrs. +</p> + +<p> +Cold Filtered Infusion of Raw Meat.—This was tried only on a single leaf, +which had most of its outer tentacles and the blade inflected in 19 hrs. During +subsequent years, I repeatedly used this infusion to test leaves which had been +experimented [page 80] on with other substances, and it was found to act most +energetically, but as no exact account of these trials was kept, they are not +here introduced. +</p> + +<p> +Mucus.—Thick and thin mucus from the bronchial tubes, placed on three +leaves, caused inflection. A leaf with thin mucus had its marginal tentacles +and blade somewhat curved inward in 5 hrs. 30 m., and greatly so in 20 hrs. The +action of this fluid no doubt is due either to the saliva or to some albuminous +matter* mingled with it, and not, as we shall see in the next chapter, to mucin +or the chemical principle of mucus. +</p> + +<p> +Saliva.—Human saliva, when evaporated, yields** from 1.14 to 1.19 per +cent. of residue; and this yields 0.25 per cent. of ashes, so that the +proportion of nitrogenous matter which saliva contains must be small. +Nevertheless, drops placed on the discs of eight leaves acted on them all. In +one case all the exterior tentacles, excepting nine, were inflected in 19 hrs. +30 m.; in another case a few became so in 2 hrs., and after 7 hrs. 30 m. all +those situated near where the drop lay, as well as the blade, were acted on. +Since making these trials, I have many scores of times just touched glands with +the handle of my scalpel wetted with saliva, to ascertain whether a leaf was in +an active condition; for this was shown in the course of a few minutes by the +bending inwards of the tentacles. The edible nest of the Chinese swallow is +formed of matter secreted by the salivary glands; two grains were added to one +ounce of distilled water (one part to 218), which was boiled for several +minutes, but did not dissolve the whole. The usual-sized drops were placed on +three leaves, and these in 1 hr. 30 m. were well, and in 2 hrs. 15 m. closely, +inflected. +</p> + +<p> +Isinglass.—Drops of a solution about as thick as milk, and of a still +thicker solution, were placed on eight leaves, and the tentacles of all became +inflected. In one case the exterior tentacles were well curved in after 6 hrs. +30 m., and the blade of the leaf to a partial extent after 24 hrs. As saliva +acted so efficiently, and yet contains so small a proportion of nitrogenous +matter, I tried how small a quantity of isinglass would act. One part was +dissolved in 218 parts of distilled water, and drops were placed on four +leaves. After 5 hrs. two of these were considerably and two moderately +inflected; after 22 hrs. the former were greatly and the latter much more +inflected. In the course of 48 hrs. +</p> + +<p class="footnote"> +* Mucus from the air-passages is said in Marshall, ‘Outlines of +Physiology,’ vol. ii. 1867, p. 364, to contain some albumen. +</p> + +<p class="footnote"> +** Müller’s ‘Elements of Physiology,’ Eng. Trans. vol. i., p. +514. [page 81] +</p> + +<p> +from the time when the drops were placed on the leaves, all four had almost +re-expanded. They were then given little bits of meat, and these acted more +powerfully than the solution. One part of isinglass was next dissolved in 437 +of water; the fluid thus formed was so thin that it could not be distinguished +from pure water. The usual-sized drops were placed on seven leaves, each of +which thus received 1/960 of a grain (.0295 mg.). Three of them were observed +for 41 hrs., but were in no way affected; the fourth and fifth had two or three +of their exterior tentacles inflected after 18 hrs.; the sixth had a few more; +and the seventh had in addition the edge of the leaf just perceptibly curved +inwards. The tentacles of the four latter leaves began to re-expand after an +additional interval of only 8 hrs. Hence the 1/960 of a grain of isinglass is +sufficient to affect very slightly the more sensitive or active leaves. On one +of the leaves, which had not been acted on by the weak solution, and on +another, which had only two of its tentacles inflected, drops of the solution +as thick as milk were placed; and next morning, after an interval of 16 hrs., +both were found with all their tentacles strongly inflected.] +</p> + +<p> +Altogether I experimented on sixty-four leaves with the above nitrogenous +fluids, the five leaves tried only with the extremely weak solution of +isinglass not being included, nor the numerous trials subsequently made, of +which no exact account was kept. Of these sixty-four leaves, sixty-three had +their tentacles and often their blades well inflected. The one which failed was +probably too old and torpid. But to obtain so large a proportion of successful +cases, care must be taken to select young and active leaves. Leaves in this +condition were chosen with equal care for the sixty-one trials with +non-nitrogenous fluids (water not included); and we have seen that not one of +these was in the least affected. We may therefore safely conclude that in the +sixty-four experiments with nitrogenous fluids the inflection of the exterior +tentacles was due to the absorption of [page 82] nitrogenous matter by the +glands of the tentacles on the disc. +</p> + +<p> +Some of the leaves which were not affected by the non-nitrogenous fluids were, +as above stated, immediately afterwards tested with bits of meat, and were thus +proved to be in an active condition. But in addition to these trials, +twenty-three of the leaves, with drops of gum, syrup, or starch, still lying on +their discs, which had produced no effect in the course of between 24 hrs. and +48 hrs., were then tested with drops of milk, urine, or albumen. Of the +twenty-three leaves thus treated, seventeen had their tentacles, and in some +cases their blades, well inflected; but their powers were somewhat impaired, +for the rate of movement was decidedly slower than when fresh leaves were +treated with these same nitrogenous fluids. This impairment, as well as the +insensibility of six of the leaves, may be attributed to injury from exosmose, +caused by the density of the fluids placed on their discs. +</p> + +<p> +[The results of a few other experiments with nitrogenous fluids may be here +conveniently given. Decoctions of some vegetables, known to be rich in +nitrogen, were made, and these acted like animal fluids. Thus, a few green peas +were boiled for some time in distilled water, and the moderately thick +decoction thus made was allowed to settle. Drops of the superincumbent fluid +were placed on four leaves, and when these were looked at after 16 hrs., the +tentacles and blades of all were found strongly inflected. I infer from a +remark by Gerhardt* that legumin is present in peas “in combination with +an alkali, forming an incoagulable solution,” and this would mingle with +boiling water. I may mention, in relation to the above and following +experiments, that according to Schiff** certain forms of albumen +</p> + +<p class="footnote"> +* Watts’ ‘Dictionary of Chemistry,’ vol. iii., p. 568. +</p> + +<p class="footnote"> +** ‘Leçons sur la Phys. de la Digestion,’ tom. i, p. 379; tom. ii. +pp. 154, 166, on legumin. [page 83] +</p> + +<p> +exist which are not coagulated by boiling water, but are converted into soluble +peptones. +</p> + +<p> +On three occasions chopped cabbage-leaves* were boiled in distilled water for 1 +hr. or for 1 1/4 hr.; and by decanting the decoction after it had been allowed +to rest, a pale dirty green fluid was obtained. The usual-sized drops were +placed on thirteen leaves. Their tentacles and blades were inflected after 4 +hrs. to a quite extraordinary degree. Next day the protoplasm within the cells +of the tentacles was found aggregated in the most strongly marked manner. I +also touched the viscid secretion round the glands of several tentacles with +minute drops of the decoction on the head of a small pin, and they became well +inflected in a few minutes. The fluid proving so powerful, one part was diluted +with three of water, and drops were placed on the discs of five leaves; and +these next morning were so much acted on that their blades were completely +doubled over. We thus see that a decoction of cabbage-leaves is nearly or quite +as potent as an infusion of raw meat. +</p> + +<p> +About the same quantity of chopped cabbage-leaves and of distilled water, as in +the last experiment, were kept in a vessel for 20 hrs. in a hot closet, but not +heated to near the boiling-point. Drops of this infusion were placed on four +leaves. One of these, after 23 hrs., was much inflected; a second slightly; a +third had only the submarginal tentacles inflected; and the fourth was not at +all affected. The power of this infusion is therefore very much less than that +of the decoction; and it is clear that the immersion of cabbage-leaves for an +hour in water at the boiling temperature is much more efficient in extracting +matter which excites Drosera than immersion during many hours in warm water. +Perhaps the contents of the cells are protected (as Schiff remarks with respect +to legumin) by the walls being formed of cellulose, and that until these are +ruptured by boiling-water, but little of the contained albuminous matter is +dissolved. We know from the strong odour of cooked cabbage-leaves that boiling +water produces some chemical change in them, and that they are thus rendered +far more digestible and nutritious to man. It is therefore an interesting +</p> + +<p class="footnote"> +* The leaves of young plants, before the heart is formed, such as were used by +me, contain 2.1 per cent. of albuminous matter, and the outer leaves of mature +plants 1.6 per cent. Watts’ ‘Dictionary of Chemistry,’ vol. +i. p. 653. [page 84] +</p> + +<p> +fact that water at this temperature extracts matter from them which excites +Drosera to an extraordinary degree. +</p> + +<p> +Grasses contain far less nitrogenous matter than do peas or cabbages. The +leaves and stalks of three common kinds were chopped and boiled for some time +in distilled water. Drops of this decoction (after having stood for 24 hrs.) +were placed on six leaves, and acted in a rather peculiar manner, of which +other instances will be given in the seventh chapter on the salts of ammonia. +After 2 hrs. 30 m. four of the leaves had their blades greatly inflected, but +not their exterior tentacles; and so it was with all six leaves after 24 hrs. +Two days afterwards the blades, as well as the few submarginal tentacles which +had been inflected, all re-expanded; and much of the fluid on their discs was +by this time absorbed. It appears that the decoction strongly excites the +glands on the disc, causing the blade to be quickly and greatly inflected; but +that the stimulus, differently from what occurs in ordinary cases, does not +spread, or only in a feeble degree, to the exterior tentacles. +</p> + +<p> +I may here add that one part of the extract of belladonna (procured from a +druggist) was dissolved in 437 of water, and drops were placed on six leaves. +Next day all six were somewhat inflected, and after 48 hrs. were completely +re-expanded. It was not the included atropine which produced this effect, for I +subsequently ascertained that it is quite powerless. I also procured some +extract of hyoscyamus from three shops, and made infusions of the same strength +as before. Of these three infusions, only one acted on some of the leaves, +which were tried. Though druggists believe that all the albumen is precipitated +in the preparation of these drugs, I cannot doubt that some is occasionally +retained; and a trace would be sufficient to excite the more sensitive leaves +of Drosera. [page 85] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0006" id="link2HCH0006"></a> +CHAPTER VI.<br/> +THE DIGESTIVE POWER OF THE SECRETION OF DROSERA.</h2> + +<p class="letter"> +The secretion rendered acid by the direct and indirect excitement of the +glands—Nature of the acid—Digestible substances—Albumen, its +digestion arrested by alkalies, recommences by the addition of an +acid—Meat—Fibrin—Syntonin—Areolar +tissue—Cartilage—Fibro-cartilage— Bone—Enamel and +dentine—Phosphate of lime—Fibrous basis of +bone—Gelatine—Chondrin— Milk, casein and +cheese—Gluten—Legumin—Pollen—Globulin—Haematin—Indigestible +substances—Epidermic productions—Fibro-elastic +tissue—Mucin—Pepsin—Urea—Chitine— +Cellulose—Gun-cotton—Chlorophyll—Fat and +oil—Starch—Action of the secretion on living seeds—Summary +and concluding remarks. +</p> + +<p> +As we have seen that nitrogenous fluids act very differently on the leaves of +Drosera from non-nitrogenous fluids, and as the leaves remain clasped for a +much longer time over various organic bodies than over inorganic bodies, such +as bits of glass, cinder, wood, &c., it becomes an interesting inquiry, +whether they can only absorb matter already in solution, or render it +soluble,—that is, have the power of digestion. We shall immediately see +that they certainly have this power, and that they act on albuminous compounds +in exactly the same manner as does the gastric juice of mammals; the digested +matter being afterwards absorbed. This fact, which will be clearly proved, is a +wonderful one in the physiology of plants. I must here state that I have been +aided throughout all my later experiments by many valuable suggestions and +assistance given me with the greatest kindness by Dr. Burdon Sanderson. [page +86] +</p> + +<p> +It may be well to premise for the sake of any reader who knows nothing about +the digestion of albuminous compounds by animals that this is effected by means +of a ferment, pepsin, together with weak hydrochloric acid, though almost any +acid will serve. Yet neither pepsin nor an acid by itself has any such power.* +We have seen that when the glands of the disc are excited by the contact of any +object, especially of one containing nitrogenous matter, the outer tentacles +and often the blade become inflected; the leaf being thus converted into a +temporary cup or stomach. At the same time the discal glands secrete more +copiously, and the secretion becomes acid. Moreover, they transmit some +influence to the glands of the exterior tentacles, causing them to pour forth a +more copious secretion, which also becomes acid or more acid than it was +before. +</p> + +<p> +As this result is an important one, I will give the evidence. The secretion of +many glands on thirty leaves, which had not been in any way excited, was tested +with litmus paper; and the secretion of twenty-two of these leaves did not in +the least affect the colour, whereas that of eight caused an exceedingly feeble +and sometimes doubtful tinge of red. Two other old leaves, however, which +appeared to have been inflected several times, acted much more decidedly on the +paper. Particles of clean glass were then placed on five of the leaves, cubes +of albumen on six, and bits of raw meat on three, on none of which was the +secretion at this time in the least acid. After an interval of 24 hrs., when +almost all the tentacles on +</p> + +<p class="footnote"> +* It appears, however, according to Schiff, and contrary to the opinion of some +physiologists, that weak hydrochloric dissolves, though slowly, a very minute +quantity of coagulated albumen. Schiff, ‘Phys. de la Digestion,’ +tom. ii. 1867, p. 25. [page 87] +</p> + +<p> +these fourteen leaves had become more or less inflected, I again tested the +secretion, selecting glands which had not as yet reached the centre or touched +any object, and it was now plainly acid. The degree of acidity of the secretion +varied somewhat on the glands of the same leaf. On some leaves, a few tentacles +did not, from some unknown cause, become inflected, as often happens; and in +five instances their secretion was found not to be in the least acid; whilst +the secretion of the adjoining and inflected tentacles on the same leaf was +decidedly acid. With leaves excited by particles of glass placed on the central +glands, the secretion which collects on the disc beneath them was much more +strongly acid than that poured forth from the exterior tentacles, which were as +yet only moderately inflected. When bits of albumen (and this is naturally +alkaline), or bits of meat were placed on the disc, the secretion collected +beneath them was likewise strongly acid. As raw meat moistened with water is +slightly acid, I compared its action on litmus paper before it was placed on +the leaves, and afterwards when bathed in the secretion; and there could not be +the least doubt that the latter was very much more acid. I have indeed tried +hundreds of times the state of the secretion on the discs of leaves which were +inflected over various objects, and never failed to find it acid. We may, +therefore, conclude that the secretion from unexcited leaves, though extremely +viscid, is not acid or only slightly so, but that it becomes acid, or much more +strongly so, after the tentacles have begun to bend over any inorganic or +organic object; and still more strongly acid after the tentacles have remained +for some time closely clasped over any object. +</p> + +<p> +I may here remind the reader that the secretion [page 88] appears to be to a +certain extent antiseptic, as it checks the appearance of mould and infusoria, +thus preventing for a time the discoloration and decay of such substances as +the white of an egg, cheese, &c. It therefore acts like the gastric juice +of the higher animals, which is known to arrest putrefaction by destroying the +microzymes. +</p> + +<p> +[As I was anxious to learn what acid the secretion contained, 445 leaves were +washed in distilled water, given me by Prof. Frankland; but the secretion is so +viscid that it is scarcely possible to scrape or wash off the whole. The +conditions were also unfavourable, as it was late in the year and the leaves +were small. Prof. Frankland with great kindness undertook to test the fluid +thus collected. The leaves were excited by clean particles of glass placed on +them 24 hrs. previously. No doubt much more acid would have been secreted had +the leaves been excited by animal matter, but this would have rendered the +analysis more difficult. Prof. Frankland informs me that the fluid contained no +trace of hydrochloric, sulphuric, tartaric, oxalic, or formic acids. This +having been ascertained, the remainder of the fluid was evaporated nearly to +dryness, and acidified with sulphuric acid; it then evolved volatile acid +vapour, which was condensed and digested with carbonate of silver. “The +weight of the silver salt thus produced was only .37 gr., much too small a +quantity for the accurate determination of the molecular weight of the acid. +The number obtained, however, corresponded nearly with that of propionic acid; +and I believe that this, or a mixture of acetic and butyric acids, were present +in the liquid. The acid doubtless belongs to the acetic or fatty series.” +</p> + +<p> +Prof. Frankland, as well as his assistant, observed (and this is an important +fact) that the fluid, “when acidified with sulphuric acid, emitted a +powerful odour like that of pepsin.” The leaves from which the secretion +had been washed were also sent to Prof. Frankland; they were macerated for some +hours, then acidified with sulphuric acid and distilled, but no acid passed +over. Therefore the acid which fresh leaves contain, as shown by their +discolouring litmus paper when crushed, must be of a different nature from that +present in the secretion. Nor was any odour of pepsin emitted by them. [page +89] +</p> + +<p> +Although it has long been known that pepsin with acetic acid has the power of +digesting albuminous compounds, it appeared advisable to ascertain whether +acetic acid could be replaced, without the loss of digestive power, by the +allied acids which are believed to occur in the secretion of Drosera, namely, +propionic, butyric, or valerianic. Dr. Burdon Sanderson was so kind as to make +for me the following experiments, the results of which are valuable, +independently of the present inquiry. Prof. Frankland supplied the acids. +</p> + +<p> +“1. The purpose of the following experiments was to determine the +digestive activity of liquids containing pepsin, when acidulated with certain +volatile acids belonging to the acetic series, in comparison with liquids +acidulated with hydrochloric acid, in proportion similar to that in which it +exists in gastric juice. +</p> + +<p> +“2. It has been determined empirically that the best results are obtained +in artificial digestion when a liquid containing two per thousand of +hydrochloric acid gas by weight is used. This corresponds to about 6.25 cubic +centimetres per litre of ordinary strong hydrochloric acid. The quantities of +propionic, butyric, and valerianic acids respectively which are required to +neutralise as much base as 6.25 cubic centimetres of HCl, are in grammes 4.04 +of propionic acid, 4.82 of butyric acid, and 5.68 of valerianic acid. It was +therefore judged expedient, in comparing the digestive powers of these acids +with that of hydrochloric acid, to use them in these proportions. +</p> + +<p> +“3. Five hundred cub. cent. of a liquid containing about 8 cub. cent. of +a glycerine extract of the mucous membrane of the stomach of a dog killed +during digestion having been prepared, 10 cub. cent. of it were evaporated and +dried at 110o. This quantity yielded 0.0031 of residue. +</p> + +<p> +“4. Of this liquid four quantities were taken which were severally +acidulated with hydrochloric, propionic, butyric, and valerianic acids, in the +proportions above indicated. Each liquid was then placed in a tube, which was +allowed to float in a water bath, containing a thermometer which indicated a +temperature of 38° to 40° Cent. Into each, a quantity of unboiled fibrin was +introduced, and the whole allowed to stand for four hours, the temperature +being maintained during the whole time, and care being taken that each +contained throughout an excess of fibrin. At the end of the period each liquid +was filtered. Of the filtrate, which of course contained as much of the fibrin +as had been digested during the four hours, [page 90] 10 cub. cent. were +measured out and evaporated, and dried at 110° as before. The residues were +respectively— +</p> + +<p> +“In the liquid containing hydrochloric acid 0.4079 ” ” +propionic acid 0.0601 ” ” butyric acid 0.1468 ” ” +valerianic acid 0.1254 +</p> + +<p> +“Hence, deducting from each of these the above-mentioned residue, left +when the digestive liquid itself was evaporated, viz. 0.0031, we have, +</p> + +<p> +“For propionic acid 0.0570 ” butyric acid 0.1437 ” valerianic +acid 0.1223 +</p> + +<p> +as compared with 0.4048 for hydrochloric acid; these several numbers expressing +the quantities of fibrin by weight digested in presence of equivalent +quantities of the respective acids under identical conditions. +</p> + +<p> +“The results of the experiment may be stated thus:—If 100 represent +the digestive power of a liquid containing pepsin with the usual proportion of +hydrochloric acid, 14.0, 35.4, and 30.2, will represent respectively the +digestive powers of the three acids under investigation. +</p> + +<p> +“5. In a second experiment in which the procedure was in every respect +the same, excepting that all the tubes were plunged into the same water-bath, +and the residues dried at 115o C., the results were as follows:— +</p> + +<p> +“Quantity of fibrin dissolved in four hours by 10 cub. cent. of the +liquid:— +</p> + +<p> +“Propionic acid 0.0563 Butyric acid 0.0835 Valerianic acid 0.0615 +</p> + +<p> +“The quantity digested by a similar liquid containing hydrochloric acid +was 0.3376. Hence, taking this as 100, the following numbers represent the +relative quantities digested by the other acids:— +</p> + +<p> +“Propionic acid 16.5 Butyric acid 24.7 Valerianic acid 16.1 +</p> + +<p> +“6. A third experiment of the same kind gave: [page 91] +</p> + +<p> +“Quantity of fibrin digested in four hours by 10 cub. cent. of the +liquid:— +</p> + +<p> +“Hydrochloric acid 0.2915 Propionic acid 0.1490 Butyric acid 0.1044 +Valerianic acid 0.0520 +</p> + +<p> +“Comparing, as before, the three last numbers with the first taken as +100, the digestive power of propionic acid is represented by 16.8; that of +butyric acid by 35.8; and that of valerianic by 17.8. +</p> + +<p> +“The mean of these three sets of observations (hydrochloric acid being +taken as 100) gives for +</p> + +<p> +“Propionic acid 15.8 Butyric acid 32.0 Valerianic acid 21.4 +</p> + +<p> +“7. A further experiment was made to ascertain whether the digestive +activity of butyric acid (which was selected as being apparently the most +efficacious) was relatively greater at ordinary temperatures than at the +temperature of the body. It was found that whereas 10 cub. cent. of a liquid +containing the ordinary proportion of hydrochloric acid digested 0.1311 gramme, +a similar liquid prepared with butyric acid digested 0.0455 gramme of fibrin. +</p> + +<p> +“Hence, taking the quantities digested with hydrochloric acid at the +temperature of the body as 100, we have the digestive power of hydrochloric +acid at the temperature of 16° to 18° Cent. represented by 44.9; that of butyric +acid at the same temperature being 15.6.” +</p> + +<p> +We here see that at the lower of these two temperatures, hydrochloric acid with +pepsin digests, within the same time, rather less than half the quantity of +fibrin compared with what it digests at the higher temperature; and the power +of butyric acid is reduced in the same proportion under similar conditions and +temperatures. We have also seen that butyric acid, which is much more +efficacious than propionic or valerianic acids, digests with pepsin at the +higher temperature less than a third of the fibrin which is digested at the +same temperature by hydrochloric acid.] [page 92] +</p> + +<p> +I will now give in detail my experiments on the digestive power of the +secretion of Drosera, dividing the substances tried into two series, namely +those which are digested more or less completely, and those which are not +digested. We shall presently see that all these substances are acted on by the +gastric juice of the higher animals in the same manner. I beg leave to call +attention to the experiments under the head albumen, showing that the secretion +loses its power when neutralised by an alkali, and recovers it when an acid is +added. +</p> + +<p> +Substances which are completely or partially digested by the Secretion of +Drosera. +</p> + +<p> +Albumen.—After having tried various substances, Dr. Burdon Sanderson +suggested to me the use of cubes of coagulated albumen or hard-boiled egg. I +may premise that five cubes of the same size as those used in the following +experiments were placed for the sake of comparison at the same time on wet moss +close to the plants of Drosera. The weather was hot, and after four days some +of the cubes were discoloured and mouldy, with their angles a little rounded; +but they were not surrounded by a zone of transparent fluid as in the case of +those undergoing digestion. Other cubes retained their angles and white colour. +After eight days all were somewhat reduced in size, discoloured, with their +angles much rounded. Nevertheless in four out of the five specimens, the +central parts were still white and opaque. So that their state differed widely, +as we shall see, from that of the cubes subjected to the action of the +secretion. +</p> + +<p> +[Experiment 1. +</p> + +<p> +Rather large cubes of albumen were first tried; the tentacles were well +inflected in 24 hrs.; after an [page 93] additional day the angles of the cubes +were dissolved and rounded;* but the cubes were too large, so that the leaves +were injured, and after seven days one died and the others were dying. Albumen +which has been kept for four or five days, and which, it may be presumed, has +begun to decay slightly, seems to act more quickly than freshly boiled eggs. As +the latter were generally used, I often moistened them with a little saliva, to +make the tentacles close more quickly. +</p> + +<p> +Experiment 2.—A cube of 1/10 of an inch (i.e. with each side 1/10 of an +inch, or 2.54 mm. in length) was placed on a leaf, and after 50 hrs. it was +converted into a sphere about 3/40 of an inch (1.905 mm.) in diameter, +surrounded by perfectly transparent fluid. After ten days the leaf re-expanded, +but there was still left on the disc a minute bit of albumen now rendered +transparent. More albumen had been given to this leaf than could be dissolved +or digested. +</p> + +<p> +Experiment 3.—Two cubes of albumen of 1/20 of an inch (1.27 mm.) were +placed on two leaves. After 46 hrs. every atom of one was dissolved, and most +of the liquefied matter was absorbed, the fluid which remained being in this, +as in all other cases, very acid and viscid. The other cube was acted on at a +rather slower rate. +</p> + +<p> +Experiment 4.—Two cubes of albumen of the same size as the last were +placed on two leaves, and were converted in 50 hrs. into two large drops of +transparent fluid; but when these were removed from beneath the inflected +tentacles, and viewed by reflected light under the microscope, fine streaks of +white opaque matter could be seen in the one, and traces of similar streaks in +the other. The drops were replaced on the leaves, which re-expanded after 10 +days; and now nothing was left except a very little transparent acid fluid. +</p> + +<p> +Experiment 5.—This experiment was slightly varied, so that the albumen +might be more quickly exposed to the action of the secretion. Two cubes, each +of about 1/40 of an inch (.635 mm.), were placed on the same leaf, and two +similar cubes on another +</p> + +<p class="footnote"> +* In all my numerous experiments on the digestion of cubes of albumen, the +angles and edges were invariably first rounded. Now, Schiff states +(‘Leçons phys. de la Digestion,’ vol. ii. 1867, page 149) that this +is characteristic of the digestion of albumen by the gastric juice of animals. +On the other hand, he remarks “les dissolutions, en chimie, ont lieu sur +toute la surface des corps en contact avec l’agent dissolvant.” +[page 94] +</p> + +<p> +leaf. These were examined after 21 hrs. 30 m., and all four were found rounded. +After 46 hrs. the two cubes on the one leaf were completely liquefied, the +fluid being perfectly transparent; on the other leaf some opaque white streaks +could still be seen in the midst of the fluid. After 72 hrs. these streaks +disappeared, but there was still a little viscid fluid left on the disc; +whereas it was almost all absorbed on the first leaf. Both leaves were now +beginning to re-expand.] +</p> + +<p> +The best and almost sole test of the presence of some ferment analogous to +pepsin in the secretion appeared to be to neutralise the acid of the secretion +with an alkali, and to observe whether the process of digestion ceased; and +then to add a little acid and observe whether the process recommenced. This was +done, and, as we shall see, with success, but it was necessary first to try two +control experiments; namely, whether the addition of minute drops of water of +the same size as those of the dissolved alkalies to be used would stop the +process of digestion; and, secondly, whether minute drops of weak hydrochloric +acid, of the same strength and size as those to be used, would injure the +leaves. The two following experiments were therefore tried:— +</p> + +<p> +Experiment 6.—Small cubes of albumen were put on three leaves, and minute +drops of distilled water on the head of a pin were added two or three times +daily. These did not in the least delay the process; for, after 48 hrs., the +cubes were completely dissolved on all three leaves. On the third day the +leaves began to re-expand, and on the fourth day all the fluid was absorbed. +</p> + +<p> +Experiment 7.—Small cubes of albumen were put on two leaves, and minute +drops of hydrochloric acid, of the strength of one part to 437 of water, were +added two or three times. This did not in the least delay, but seemed rather to +hasten, the process of digestion; for every trace of the albumen disappeared in +24 hrs. 30 m. After three days the leaves partially re-expanded, and by this +time almost all the viscid fluid on their discs was absorbed. It is almost +superfluous to state that [page 95] cubes of albumen of the same size as those +above used, left for seven days in a little hydrochloric acid of the above +strength, retained all their angles as perfect as ever. +</p> + +<p> +Experiment 8.—Cubes of albumen (of 1/20 of an inch, or 2.54 mm.) were +placed on five leaves, and minute drops of a solution of one part of carbonate +of soda to 437 of water were added at intervals to three of them, and drops of +carbonate of potash of the same strength to the other two. The drops were given +on the head of a rather large pin, and I ascertained that each was equal to +about 1/10 of a minim (.0059 ml.), so that each contained only 1/4800 of a +grain (.0135 mg.) of the alkali. This was not sufficient, for after 46 hrs. all +five cubes were dissolved. +</p> + +<p> +Experiment 9.—The last experiment was repeated on four leaves, with this +difference, that drops of the same solution of carbonate of soda were added +rather oftener, as often as the secretion became acid, so that it was much more +effectually neutralised. And now after 24 hrs. the angles of three of the cubes +were not in the least rounded, those of the fourth being so in a very slight +degree. Drops of extremely weak hydrochloric acid (viz. one part to 847 of +water) were then added, just enough to neutralise the alkali which was still +present; and now digestion immediately recommenced, so that after 23 hrs. 30 m. +three of the cubes were completely dissolved, whilst the fourth was converted +into a minute sphere, surrounded by transparent fluid; and this sphere next day +disappeared. +</p> + +<p> +Experiment 10.—Stronger solutions of carbonate of soda and of potash were +next used, viz. one part to 109 of water; and as the same-sized drops were +given as before, each drop contained 1/1200 of a grain (.0539 mg.) of either +salt. Two cubes of albumen (each about 1/40 of an inch, or .635 mm.) were +placed on the same leaf, and two on another. Each leaf received, as soon as the +secretion became slightly acid (and this occurred four times within 24 hrs.), +drops either of the soda or potash, and the acid was thus effectually +neutralised. The experiment now succeeded perfectly, for after 22 hrs. the +angles of the cubes were as sharp as they were at first, and we know from +experiment 5 that such small cubes would have been completely rounded within +this time by the secretion in its natural state. Some of the fluid was now +removed with blotting-paper from the discs of the leaves, and minute drops of +hydrochloric acid of the strength of the one part to 200 of water was added. +Acid of this greater strength was used as the solutions of the alkalies were +stronger. The [page 96] process of digestion now commenced, so that within 48 +hrs. from the time when the acid was given the four cubes were not only +completely dissolved, but much of the liquefied albumen was absorbed. +</p> + +<p> +Experiment 11.—Two cubes of albumen (1/40 of an inch, or .635 mm.) were +placed on two leaves, and were treated with alkalies as in the last experiment, +and with the same result; for after 22 hrs. they had their angles perfectly +sharp, showing that the digestive process had been completely arrested. I then +wished to ascertain what would be the effect of using stronger hydrochloric +acid; so I added minute drops of the strength of 1 per cent. This proved rather +too strong, for after 48 hrs. from the time when the acid was added one cube +was still almost perfect, and the other only very slightly rounded, and both +were stained slightly pink. This latter fact shows that the leaves were +injured,* for during the normal process of digestion the albumen is not thus +coloured, and we can thus understand why the cubes were not dissolved.] +</p> + +<p> +From these experiments we clearly see that the secretion has the power of +dissolving albumen, and we further see that if an alkali is added, the process +of digestion is stopped, but immediately recommences as soon as the alkali is +neutralised by weak hydrochloric acid. Even if I had tried no other experiments +than these, they would have almost sufficed to prove that the glands of Drosera +secrete some ferment analogous to pepsin, which in presence of an acid gives to +the secretion its power of dissolving albuminous compounds. +</p> + +<p> +Splinters of clean glass were scattered on a large number of leaves, and these +became moderately inflected. They were cut off and divided into three lots; two +of them, after being left for some time in a little distilled water, were +strained, and some dis- +</p> + +<p class="footnote"> +* Sachs remarks (‘Traité de Bot.’ 1874, p. 774), that cells which +are killed by freezing, by too great heat, or by chemical agents, allow all +their colouring matter to escape into the surrounding water. [page 97] +</p> + +<p> +coloured, viscid, slightly acid fluid was thus obtained. The third lot was well +soaked in a few drops of glycerine, which is well known to dissolve pepsin. +Cubes of albumen (1/20 of an inch) were now placed in the three fluids in +watch-glasses, some of which were kept for several days at about 90° Fahr. +(32°.2 Cent.), and others at the temperature of my room; but none of the cubes +were dissolved, the angles remaining as sharp as ever. This fact probably +indicates that the ferment is not secreted until the glands are excited by the +absorption of a minute quantity of already soluble animal matter,—a +conclusion which is supported by what we shall hereafter see with respect to +Dionaea. Dr. Hooker likewise found that, although the fluid within the pitchers +of Nepenthes possesses extraordinary power of digestion, yet when removed from +the pitchers before they have been excited and placed in a vessel, it has no +such power, although it is already acid; and we can account for this fact only +on the supposition that the proper ferment is not secreted until some exciting +matter is absorbed. +</p> + +<p> +On three other occasions eight leaves were strongly excited with albumen +moistened with saliva; they were then cut off, and allowed to soak for several +hours or for a whole day in a few drops of glycerine. Some of this extract was +added to a little hydrochloric acid of various strengths (generally one to 400 +of water), and minute cubes of albumen were placed in the mixture.* In two of +these trials the cubes were not in the least acted on; but in the third +</p> + +<p class="footnote"> +* As a control experiment bits of albumen were placed in the same glycerine +with hydrochloric acid of the same strength; and the albumen, as might have +been expected, was not in the least affected after two days. [page 98] +</p> + +<p> +the experiment was successful. For in a vessel containing two cubes, both were +reduced in size in 3 hrs.; and after 24 hrs. mere streaks of undissolved +albumen were left. In a second vessel, containing two minute ragged bits of +albumen, both were likewise reduced in size in 3 hrs., and after 24 hrs. +completely disappeared. I then added a little weak hydrochloric acid to both +vessels, and placed fresh cubes of albumen in them; but these were not acted +on. This latter fact is intelligible according to the high authority of +Schiff,* who has demonstrated, as he believes, in opposition to the view held +by some physiologists, that a certain small amount of pepsin is destroyed +during the act of digestion. So that if my solution contained, as is probable, +an extremely small amount of the ferment, this would have been consumed by the +dissolution of the cubes of albumen first given; none being left when the +hydrochloric acid was added. The destruction of the ferment during the process +of digestion, or its absorption after the albumen had been converted into a +peptone, will also account for only one out of the three latter sets of +experiments having been successful. +</p> + +<p> +Digestion of Roast Meat.—Cubes of about 1/20 of an inch (1.27 mm.) of +moderately roasted meat were placed on five leaves which became in 12 hrs. +closely inflected. After 48 hrs. I gently opened one leaf, and the meat now +consisted of a minute central sphere, partially digested and surrounded by a +thick envelope of transparent viscid fluid. The whole, without being much +disturbed, was removed and placed under the microscope. In the central part the +transverse striae on the muscular fibres were quite distinct; and it was +</p> + +<p class="footnote"> +* ‘Leçons phys. de la Digestion,’ 1867, tom. ii. pp. 114-126. [page +99] +</p> + +<p> +interesting to observe how gradually they disappeared, when the same fibre was +traced into the surrounding fluid. They disappeared by the striae being +replaced by transverse lines formed of excessively minute dark points, which +towards the exterior could be seen only under a very high power; and ultimately +these points were lost. When I made these observations, I had not read +Schiff’s account* of the digestion of meat by gastric juice, and I did +not understand the meaning of the dark points. But this is explained in the +following statement, and we further see how closely similar is the process of +digestion by gastric juice and by the secretion of Drosera. +</p> + +<p class="p1"> +<small>“On a dit le suc gastrique faisait perdre à la fibre musculaire +ses stries transversales. Ainsi énoncée, cette proposition pourrait donner lieu +à une équivoque, car ce qui se perd, ce n’est que <i>l’aspect</i> +extérieur de la striature et non les éléments anatomiques qui la composent. On +sait que les stries qui donnent un aspect si caractéristique à la fibre +musculaire, sont le résultat de la juxtaposition et du parallélisme des +corpuscules élémentaires, placés, à distances égales, dans l’intérieur +des fibrilles contiguës. Or, dès que le tissu connectif qui relie entre elles +les fibrilles élémentaires vient à se gonfler et à se dissoudre, et que les +fibrilles elles-mêmes se dissocient, ce parallélisme est détruit et avec lui +l’aspect, le phénomène optique des stries. Si, après la désagrégation des +fibres, on examine au microscope les fibrilles élémentaires, on distingue +encore très-nettement à leur intérieur les corpuscules, et on continue à les +voir, de plus en plus pâles, jusqu’au moment où les fibrilles elles-mêmes +se liquéfient et disparaissent dans le suc gastrique. Ce qui constitue la +striature, à proprement parler, n’est donc pas détruit, avant la +liquéfaction de la fibre charnue elle-même.”</small> +</p> + +<p class="p1"> +In the viscid fluid surrounding the central sphere of undigested meat there +were globules of fat and little bits of fibro-elastic tissue; neither of which +were in +</p> + +<p class="footnote"> +* ‘Leçons phys. de la Digestion,’ tom. ii. p. 145. [page 100] +</p> + +<p> +the least digested. There were also little free parallelograms of yellowish, +highly translucent matter. Schiff, in speaking of the digestion of meat by +gastric juice, alludes to such parallelograms, and says:— +</p> + +<p class="p1"> +<small>“Le gonflement par lequel commence la digestion de la viande, +résulte de l’action du suc gastrique acide sur le tissu connectif qui se +dissout d’abord, et qui, par sa liquéfaction, désagrége les fibrilles. +Celles-ci se dissolvent ensuite en grande partie, mais, avant de passer à +l’état liquide, elles tendent à se briser en petits fragments +transversaux. Les ‘<i>sarcous elements</i>’ de Bowman, qui ne sont +autre chose que les produits de cette division transversale des fibrilles +élémentaires, peuvent être préparés et isolés à l’aide du suc gastrique, +pourvu qu’on n’attend pas jusqu’à la liquéfaction complète du +muscle.”</small> +</p> + +<p class="p1"> +After an interval of 72 hrs., from the time when the five cubes were placed on +the leaves, I opened the four remaining ones. On two nothing could be seen but +little masses of transparent viscid fluid; but when these were examined under a +high power, fat-globules, bits of fibro-elastic tissue, and some few +parallelograms of sarcous matter, could be distinguished, but not a vestige of +transverse striae. On the other two leaves there were minute spheres of only +partially digested meat in the centre of much transparent fluid. +</p> + +<p> +Fibrin.—Bits of fibrin were left in water during four days, whilst the +following experiments were tried, but they were not in the least acted on. The +fibrin which I first used was not pure, and included dark particles: it had +either not been well prepared or had subsequently undergone some change. Thin +portions, about 1/10 of an inch square, were placed on several leaves, and +though the fibrin was soon liquefied, the whole was never dissolved. Smaller +particles were then placed on four leaves, and minute [page 101] drops of +hydrochloric acid (one part to 437 of water) were added; this seemed to hasten +the process of digestion, for on one leaf all was liquified and absorbed after +20 hrs.; but on the three other leaves some undissolved residue was left after +48 hrs. It is remarkable that in all the above and following experiments, as +well as when much larger bits of fibrin were used, the leaves were very little +excited; and it was sometimes necessary to add a little saliva to induce +complete inflection. The leaves, moreover, began to re-expand after only 48 +hrs., whereas they would have remained inflected for a much longer time had +insects, meat, cartilage, albumen, &c., been placed on them. +</p> + +<p> +I then tried some pure white fibrin, sent me by Dr. Burdon Sanderson. +</p> + +<p> +[Experiment 1.—Two particles, barely 1/20 of an inch (1.27 mm.) square, +were placed on opposite sides of the same leaf. One of these did not excite the +surrounding tentacles, and the gland on which it rested soon dried. The other +particle caused a few of the short adjoining tentacles to be inflected, the +more distant ones not being affected. After 24 hrs. both were almost, and after +72 hrs. completely, dissolved. +</p> + +<p> +Experiment 2.—The same experiment with the same result, only one of the +two bits of fibrin exciting the short surrounding tentacles. This bit was so +slowly acted on that after a day I pushed it on to some fresh glands. In three +days from the time when it was first placed on the leaf it was completely +dissolved. +</p> + +<p> +Experiment 3.—Bits of fibrin of about the same size as before were placed +on the discs of two leaves; these caused very little inflection in 23 hrs., but +after 48 hrs. both were well clasped by the surrounding short tentacles, and +after an additional 24 hrs. were completely dissolved. On the disc of one of +these leaves much clear acid fluid was left. +</p> + +<p> +Experiment 4.—Similar bits of fibrin were placed on the discs of two +leaves; as after 2 hrs. the glands seemed rather dry, they were freely +moistened with saliva; this soon caused strong inflection both of the tentacles +and blades, with copious [page 102] secretion from the glands. In 18 hrs. the +fibrin was completely liquefied, but undigested atoms still floated in the +liquid; these, however, disappeared in under two additional days.] +</p> + +<p> +From these experiments it is clear that the secretion completely dissolves pure +fibrin. The rate of dissolution is rather slow; but this depends merely on this +substance not exciting the leaves sufficiently, so that only the immediately +adjoining tentacles are inflected, and the supply of secretion is small. +</p> + +<p> +Syntonin.—This substance, extracted from muscle, was kindly prepared for +me by Dr. Moore. Very differently from fibrin, it acts quickly and +energetically. Small portions placed on the discs of three leaves caused their +tentacles and blades to be strongly inflected within 8 hrs.; but no further +observations were made. It is probably due to the presence of this substance +that raw meat is too powerful a stimulant, often injuring or even killing the +leaves. +</p> + +<p> +Areolar Tissue.—Small portions of this tissue from a sheep were placed on +the discs of three leaves; these became moderately well inflected in 24 hrs., +but began to re-expand after 48 hrs., and were fully re-expanded in 72 hrs., +always reckoning from the time when the bits were first given. This substance, +therefore, like fibrin, excites the leaves for only a short time. The residue +left on the leaves, after they were fully re-expanded, was examined under a +high power and found much altered, but, owing to the presence of a quantity of +elastic tissue, which is never acted on, could hardly be said to be in a +liquefied condition. +</p> + +<p> +Some areolar tissue free from elastic tissue was next procured from the +visceral cavity of a toad, and moderately sized, as well as very small, bits +were placed on five leaves. After 24 hrs. two of the bits [page 103] were +completely liquefied; two others were rendered transparent, but not quite +liquefied; whilst the fifth was but little affected. Several glands on the +three latter leaves were now moistened with a little saliva, which soon caused +much inflection and secretion, with the result that in the course of 12 +additional hrs. one leaf alone showed a remnant of undigested tissue. On the +discs of the four other leaves (to one of which a rather large bit had been +given) nothing was left except some transparent viscid fluid. I may add that +some of this tissue included points of black pigment, and these were not at all +affected. As a control experiment, small portions of this tissue were left in +water and on wet moss for the same length of time, and remained white and +opaque. From these facts it is clear that areolar tissue is easily and quickly +digested by the secretion; but that it does not greatly excite the leaves. +</p> + +<p> +Cartilage.—Three cubes (1/20 of an inch or 1.27 mm.) of white, +translucent, extremely tough cartilage were cut from the end of a slightly +roasted leg-bone of a sheep. These were placed on three leaves, borne by poor, +small plants in my greenhouse during November; and it seemed in the highest +degree improbable that so hard a substance would be digested under such +unfavourable circumstances. Nevertheless, after 48 hrs., the cubes were largely +dissolved and converted into minute spheres, surrounded by transparent, very +acid fluid. Two of these spheres were completely softened to their centres; +whilst the third still contained a very small irregularly shaped core of solid +cartilage. Their surfaces were seen under the microscope to be curiously marked +by prominent ridges, showing that the cartilage had been unequally corroded by +the secretion. I need hardly [page 104] say that cubes of the same cartilage, +kept in water for the same length of time, were not in the least affected. +</p> + +<p> +During a more favourable season, moderately sized bits of the skinned ear of a +cat, which includes cartilage, areolar and elastic tissue, were placed on three +leaves. Some of the glands were touched with saliva, which caused prompt +inflection. Two of the leaves began to re-expand after three days, and the +third on the fifth day. The fluid residue left on their discs was now examined, +and consisted in one case of perfectly transparent, viscid matter; in the other +two cases, it contained some elastic tissue and apparently remnants of half +digested areolar tissue. +</p> + +<p> +Fibro-cartilage (from between the vertebrae of the tail of a sheep). Moderately +sized and small bits (the latter about 1/20 of an inch) were placed on nine +leaves. Some of these were well and some very little inflected. In the latter +case the bits were dragged over the discs, so that they were well bedaubed with +the secretion, and many glands thus irritated. All the leaves re-expanded after +only two days; so that they were but little excited by this substance. The bits +were not liquefied, but were certainly in an altered condition, being swollen, +much more transparent, and so tender as to disintegrate very easily. My son +Francis prepared some artificial gastric juice, which was proved efficient by +quickly dissolving fibrin, and suspended portions of the fibro-cartilage in it. +These swelled and became hyaline, exactly like those exposed to the secretion +of Drosera, but were not dissolved. This result surprised me much, as two +physiologists were of opinion that fibro-cartilage would be easily digested by +gastric juice. I therefore asked Dr. Klein to examine the specimens; and [page +105] he reports that the two which had been subjected to artificial gastric +juice were “in that state of digestion in which we find connective tissue +when treated with an acid, viz. swollen, more or less hyaline, the fibrillar +bundles having become homogeneous and lost their fibrillar structure.” In +the specimens which had been left on the leaves of Drosera, until they +re-expanded, “parts were altered, though only slightly so, in the same +manner as those subjected to the gastric juice as they had become more +transparent, almost hyaline, with the fibrillation of the bundles +indistinct.” Fibro-cartilage is therefore acted on in nearly the same +manner by gastric juice and by the secretion of Drosera. +</p> + +<p> +Bone.—Small smooth bits of the dried hyoidal bone of a fowl moistened +with saliva were placed on two leaves, and a similarly moistened splinter of an +extremely hard, broiled mutton-chop bone on a third leaf. These leaves soon +became strongly inflected, and remained so for an unusual length of time; +namely, one leaf for ten and the other two for nine days. The bits of bone were +surrounded all the time by acid secretion. When examined under a weak power, +they were found quite softened, so that they were readily penetrated by a blunt +needle, torn into fibres, or compressed. Dr. Klein was so kind as to make +sections of both bones and examine them. He informs me that both presented the +normal appearance of decalcified bone, with traces of the earthy salts +occasionally left. The corpuscles with their processes were very distinct in +most parts; but in some parts, especially near the periphery of the hyoidal +bone, none could be seen. Other parts again appeared amorphous, with even the +longitudinal striation of bone not distinguishable. This amorphous structure, +[page 106] as Dr. Klein thinks, may be the result either of the incipient +digestion of the fibrous basis or of all the animal matter having been removed, +the corpuscles being thus rendered invisible. A hard, brittle, yellowish +substance occupied the position of the medulla in the fragments of the hyoidal +bone. +</p> + +<p> +As the angles and little projections of the fibrous basis were not in the least +rounded or corroded, two of the bits were placed on fresh leaves. These by the +next morning were closely inflected, and remained so,—the one for six and +the other for seven days,—therefore for not so long a time as on the +first occasion, but for a much longer time than ever occurs with leaves +inflected over inorganic or even over many organic bodies. The secretion during +the whole time coloured litmus paper of a bright red; but this may have been +due to the presence of the acid super-phosphate of lime. When the leaves +re-expanded, the angles and projections of the fibrous basis were as sharp as +ever. I therefore concluded, falsely as we shall presently see, that the +secretion cannot touch the fibrous basis of bone. The more probable explanation +is that the acid was all consumed in decomposing the phosphate of lime which +still remained; so that none was left in a free state to act in conjunction +with the ferment on the fibrous basis. +</p> + +<p> +Enamel and Dentine.—As the secretion decalcified ordinary bone, I +determined to try whether it would act on enamel and dentine, but did not +expect that it would succeed with so hard a substance as enamel. Dr. Klein gave +me some thin transverse slices of the canine tooth of a dog; small angular +fragments of which were placed on four leaves; and these were examined each +succeeding day at the same hour. The results are, I think, worth giving in +detail.] [page 107] +</p> + +<p> +[Experiment 1.—May 1st, fragment placed on leaf; 3rd, tentacles but +little inflected, so a little saliva was added; 6th, as the tentacles were not +strongly inflected, the fragment was transferred to another leaf, which acted +at first slowly, but by the 9th closely embraced it. On the 11th this second +leaf began to re-expand; the fragment was manifestly softened, and Dr. Klein +reports, “a great deal of enamel and the greater part of the dentine +decalcified.” +</p> + +<p> +Experiment 2.—May 1st, fragment placed on leaf; 2nd, tentacles fairly +well inflected, with much secretion on the disc, and remained so until the 7th, +when the leaf re-expanded. The fragment was now transferred to a fresh leaf, +which next day (8th) was inflected in the strongest manner, and thus remained +until the 11th, when it re-expanded. Dr. Klein reports, “a great deal of +enamel and the greater part of the dentine decalcified.” +</p> + +<p> +Experiment 3.—May 1st, fragment moistened with saliva and placed on a +leaf, which remained well inflected until 5th, when it re-expanded. The enamel +was not at all, and the dentine only slightly, softened. The fragment was now +transferred to a fresh leaf, which next morning (6th) was strongly inflected, +and remained so until the 11th. The enamel and dentine both now somewhat +softened; and Dr. Klein reports, “less than half the enamel, but the +greater part of the dentine decalcified.” +</p> + +<p> +Experiment 4.—May 1st, a minute and thin bit of dentine, moistened with +saliva, was placed on a leaf, which was soon inflected, and re-expanded on the +5th. The dentine had become as flexible as thin paper. It was then transferred +to a fresh leaf, which next morning (6th) was strongly inflected, and reopened +on the 10th. The decalcified dentine was now so tender that it was torn into +shreds merely by the force of the re-expanding tentacles.] +</p> + +<p> +From these experiments it appears that enamel is attacked by the secretion with +more difficulty than dentine, as might have been expected from its extreme +hardness; and both with more difficulty than ordinary bone. After the process +of dissolution has once commenced, it is carried on with greater ease; this may +be inferred from the leaves, to which the fragments were transferred, becoming +in all four cases strongly inflected in the course of a single day; whereas the +first set of leaves acted much less quickly and [page 108] energetically. The +angles or projections of the fibrous basis of the enamel and dentine (except, +perhaps, in No. 4, which could not be well observed) were not in the least +rounded; and Dr. Klein remarks that their microscopical structure was not +altered. But this could not have been expected, as the decalcification was not +complete in the three specimens which were carefully examined. +</p> + +<p> +Fibrous Basis of Bone.—I at first concluded, as already stated, that the +secretion could not digest this substance. I therefore asked Dr. Burdon +Sanderson to try bone, enamel, and dentine, in artificial gastric juice, and he +found that they were after a considerable time completely dissolved. Dr. Klein +examined some of the small lamellae, into which part of the skull of a cat +became broken up after about a week’s immersion in the fluid, and he +found that towards the edges the “matrix appeared rarefied, thus +producing the appearance as if the canaliculi of the bone-corpuscles had become +larger. Otherwise the corpuscles and their canaliculi were very +distinct.” So that with bone subjected to artificial gastric juice +complete decalcification precedes the dissolution of the fibrous basis. Dr. +Burdon Sanderson suggested to me that the failure of Drosera to digest the +fibrous basis of bone, enamel, and dentine, might be due to the acid being +consumed in the decomposition of the earthy salts, so that there was none left +for the work of digestion. Accordingly, my son thoroughly decalcified the bone +of a sheep with weak hydrochloric acid; and seven minute fragments of the +fibrous basis were placed on so many leaves, four of the fragments being first +damped with saliva to aid prompt inflection. All seven leaves became inflected, +but only very moderately, in the course of a day. [page 109] They quickly began +to re-expand; five of them on the second day, and the other two on the third +day. On all seven leaves the fibrous tissue was converted into perfectly +transparent, viscid, more or less liquefied little masses. In the middle, +however, of one, my son saw under a high power a few corpuscles, with traces of +fibrillation in the surrounding transparent matter. From these facts it is +clear that the leaves are very little excited by the fibrous basis of bone, but +that the secretion easily and quickly liquefies it, if thoroughly decalcified. +The glands which had remained in contact for two or three days with the viscid +masses were not discoloured, and apparently had absorbed little of the +liquefied tissue, or had been little affected by it. +</p> + +<p> +Phosphate of Lime.—As we have seen that the tentacles of the first set of +leaves remained clasped for nine or ten days over minute fragments of bone, and +the tentacles of the second set for six or seven days over the same fragments, +I was led to suppose that it was the phosphate of lime, and not any included +animal matter, which caused such long continued inflection. It is at least +certain from what has just been shown that this cannot have been due to the +presence of the fibrous basis. With enamel and dentine (the former of which +contains only 4 per cent. of organic matter) the tentacles of two successive +sets of leaves remained inflected altogether for eleven days. In order to test +my belief in the potency of phosphate of lime, I procured some from Prof. +Frankland absolutely free of animal matter and of any acid. A small quantity +moistened with water was placed on the discs of two leaves. One of these was +only slightly affected; the other remained closely inflected for ten days, when +a few of the tentacles began to [page 110] re-expand, the rest being much +injured or killed. I repeated the experiment, but moistened the phosphate with +saliva to insure prompt inflection; one leaf remained inflected for six days +(the little saliva used would not have acted for nearly so long a time) and +then died; the other leaf tried to re-expand on the sixth day, but after nine +days failed to do so, and likewise died. Although the quantity of phosphate +given to the above four leaves was extremely small, much was left in every case +undissolved. A larger quantity wetted with water was next placed on the discs +of three leaves; and these became most strongly inflected in the course of 24 +hrs. They never re-expanded; on the fourth day they looked sickly, and on the +sixth were almost dead. Large drops of not very viscid fluid hung from their +edges during the six days. This fluid was tested each day with litmus paper, +but never coloured it; and this circumstance I do not understand, as the +superphosphate of lime is acid. I suppose that some superphosphate must have +been formed by the acid of the secretion acting on the phosphate, but that it +was all absorbed and injured the leaves; the large drops which hung from their +edges being an abnormal and dropsical secretion. Anyhow, it is manifest that +the phosphate of lime is a most powerful stimulant. Even small doses are more +or less poisonous, probably on the same principle that raw meat and other +nutritious substances, given in excess, kill the leaves. Hence the conclusion, +that the long continued inflection of the tentacles over fragments of bone, +enamel, and dentine, is caused by the presence of phosphate of lime, and not of +any included animal matter, is no doubt correct. +</p> + +<p> +Gelatine.—I used pure gelatine in thin sheets given [page 111] me by +Prof. Hoffmann. For comparison, squares of the same size as those placed on the +leaves were left close by on wet moss. These soon swelled, but retained their +angles for three days; after five days they formed rounded, softened masses, +but even on the eighth day a trace of gelatine could still be detected. Other +squares were immersed in water, and these, though much swollen, retained their +angles for six days. Squares of 1/10 of an inch (2.54 mm.), just moistened with +water, were placed on two leaves; and after two or three days nothing was left +on them but some acid viscid fluid, which in this and other cases never showed +any tendency to regelatinise; so that the secretion must act on the gelatine +differently to what water does, and apparently in the same manner as gastric +juice.* Four squares of the same size as before were then soaked for three days +in water, and placed on large leaves; the gelatine was liquefied and rendered +acid in two days, but did not excite much inflection. The leaves began to +re-expand after four or five days, much viscid fluid being left on their discs, +as if but little had been absorbed. One of these leaves, as soon as it +re-expanded, caught a small fly, and after 24 hrs. was closely inflected, +showing how much more potent than gelatine is the animal matter absorbed from +an insect. Some larger pieces of gelatine, soaked for five days in water, were +next placed on three leaves, but these did not become much inflected until the +third day; nor was the gelatine completely liquefied until the fourth day. On +this day one leaf began to re-expand; the second on the fifth; and third on the +sixth. These several facts +</p> + +<p class="footnote"> +* Dr. Lauder Brunton, ‘Handbook for the Phys. Laboratory,’ 1873, +pp. 477, 487; Schiff, ‘Leçons phys. de la Digestion,’ 1867, p. 249. +[page 112] +</p> + +<p> +prove that gelatine is far from acting energetically on Drosera. +</p> + +<p> +In the last chapter it was shown that a solution of isinglass of commerce, as +thick as milk or cream, induces strong inflection. I therefore wished to +compare its action with that of pure gelatine. Solutions of one part of both +substances to 218 of water were made; and half-minim drops (.0296 ml.) were +placed on the discs of eight leaves, so that each received 1/480 of a grain, or +.135 mg. The four with the isinglass were much more strongly inflected than the +other four. I conclude therefore that isinglass contains some, though perhaps +very little, soluble albuminous matter. As soon as these eight leaves +re-expanded, they were given bits of roast meat, and in some hours all became +greatly inflected; again showing how much more meat excites Drosera than does +gelatine or isinglass. This is an interesting fact, as it is well known that +gelatine by itself has little power of nourishing animals.* +</p> + +<p> +Chondrin.—This was sent me by Dr. Moore in a gelatinous state. Some was +slowly dried, and a small chip was placed on a leaf, and a much larger chip on +a second leaf. The first was liquefied in a day; the larger piece was much +swollen and softened, but was not completely liquefied until the third day. The +undried jelly was next tried, and as a control experiment small cubes were left +in water for four days and retained their angles. Cubes of the same size were +placed on two leaves, and larger cubes on two other leaves. The tentacles and +laminae of the latter were closely inflected after 22 hrs., but those of the +</p> + +<p class="footnote"> +* Dr. Lauder Brunton gives in the ‘Medical Record,’ January 1873, +p. 36, an account of Voit’s view of the indirect part which gelatine +plays in nutrition. [page 113] +</p> + +<p> +two leaves with the smaller cubes only to a moderate degree. The jelly on all +four was by this time liquefied, and rendered very acid. The glands were +blackened from the aggregation of their protoplasmic contents. In 46 hrs. from +the time when the jelly was given, the leaves had almost re-expanded, and +completely so after 70 hrs.; and now only a little slightly adhesive fluid was +left unabsorbed on their discs. +</p> + +<p> +One part of chondrin jelly was dissolved in 218 parts of boiling water, and +half-minim drops were given to four leaves; so that each received about 1/480 +of a grain (.135 mg.) of the jelly; and, of course, much less of dry chondrin. +This acted most powerfully, for after only 3 hrs. 30 m. all four leaves were +strongly inflected. Three of them began to re-expand after 24 hrs., and in 48 +hrs. were completely open; but the fourth had only partially re-expanded. All +the liquefied chondrin was by this time absorbed. Hence a solution of chondrin +seems to act far more quickly and energetically than pure gelatine or +isinglass; but I am assured by good authorities that it is most difficult, or +impossible, to know whether chondrin is pure, and if it contained any +albuminous compound, this would have produced the above effects. Nevertheless, +I have thought these facts worth giving, as there is so much doubt on the +nutritious value of gelatine; and Dr. Lauder Brunton does not know of any +experiments with respect to animals on the relative value of gelatine and +chondrin. +</p> + +<p> +Milk.—We have seen in the last chapter that milk acts most powerfully on +the leaves; but whether this is due to the contained casein or albumen, I know +not. Rather large drops of milk excite so much secretion (which is very acid) +that it sometimes trickles down [page 114] from the leaves, and this is +likewise characteristic of chemically prepared casein. Minute drops of milk, +placed on leaves, were coagulated in about ten minutes. Schiff denies* that the +coagulation of milk by gastric juice is exclusively due to the acid which is +present, but attributes it in part to the pepsin; and it seems doubtful whether +with Drosera the coagulation can be wholly due to the acid, as the secretion +does not commonly colour litmus paper until the tentacles have become well +inflected; whereas the coagulation commences, as we have seen, in about ten +minutes. Minute drops of skimmed milk were placed on the discs of five leaves; +and a large proportion of the coagulated matter or curd was dissolved in 6 hrs. +and still more completely in 8 hrs. These leaves re-expanded after two days, +and the viscid fluid left on their discs was then carefully scraped off and +examined. It seemed at first sight as if all the casein had not been dissolved, +for a little matter was left which appeared of a whitish colour by reflected +light. But this matter, when examined under a high power, and when compared +with a minute drop of skimmed milk coagulated by acetic acid, was seen to +consist exclusively of oil-globules, more or less aggregated together, with no +trace of casein. As I was not familiar with the microscopical appearance of +milk, I asked Dr. Lauder Brunton to examine the slides, and he tested the +globules with ether, and found that they were dissolved. We may, therefore, +conclude that the secretion quickly dissolves casein, in the state in which it +exists in milk. +</p> + +<p> +Chemically Prepared Casein.—This substance, which +</p> + +<p class="footnote"> +* ‘Leçons,’ &c. tom. ii. page 151. [page 115] +</p> + +<p> +is insoluble in water, is supposed by many chemists to differ from the casein +of fresh milk. I procured some, consisting of hard globules, from Messrs. +Hopkins and Williams, and tried many experiments with it. Small particles and +the powder, both in a dry state and moistened with water, caused the leaves on +which they were placed to be inflected very slowly, generally not until two +days had elapsed. Other particles, wetted with weak hydrochloric acid (one part +to 437 of water) acted in a single day, as did some casein freshly prepared for +me by Dr. Moore. The tentacles commonly remained inflected for from seven to +nine days; and during the whole of this time the secretion was strongly acid. +Even on the eleventh day some secretion left on the disc of a fully re-expanded +leaf was strongly acid. The acid seems to be secreted quickly, for in one case +the secretion from the discal glands, on which a little powdered casein had +been strewed, coloured litmus paper, before any of the exterior tentacles were +inflected. +</p> + +<p> +Small cubes of hard casein, moistened with water, were placed on two leaves; +after three days one cube had its angles a little rounded, and after seven days +both consisted of rounded softened masses, in the midst of much viscid and acid +secretion; but it must not be inferred from this fact that the angles were +dissolved, for cubes immersed in water were similarly acted on. After nine days +these leaves began to re-expand, but in this and other cases the casein did not +appear, as far as could be judged by the eye, much, if at all, reduced in bulk. +According to Hoppe-Seyler and Lubavin* casein consists of an albuminous, with +</p> + +<p class="footnote"> +* Dr. Lauder Brunton, ‘Handbook for Phys. Lab.’ p. 529. [page 116] +</p> + +<p> +a non-albuminous, substance; and the absorption of a very small quantity of the +former would excite the leaves, and yet not decrease the casein to a +perceptible degree. Schiff asserts*—and this is an important fact for +us—that “la casine purifie des chemistes est un corps presque +compltement inattaquable par le suc gastrique.” So that here we have +another point of accordance between the secretion of Drosera and gastric juice, +as both act so differently on the fresh casein of milk, and on that prepared by +chemists. +</p> + +<p> +A few trials were made with cheese; cubes of 1/20 of an inch (1.27 mm.) were +placed on four leaves, and these after one or two days became well inflected, +their glands pouring forth much acid secretion. After five days they began to +re-expand, but one died, and some of the glands on the other leaves were +injured. Judging by the eye, the softened and subsided masses of cheese, left +on the discs, were very little or not at all reduced in bulk. We may, however, +infer from the time during which the tentacles remained inflected,—from +the changed colour of some of the glands,—and from the injury done to +others, that matter had been absorbed from the cheese. +</p> + +<p> +Legumin.—I did not procure this substance in a separate state; but there +can hardly be a doubt that it would be easily digested, judging from the +powerful effect produced by drops of a decoction of green peas, as described in +the last chapter. Thin slices of a dried pea, after being soaked in water, were +placed on two leaves; these became somewhat inflected in the course of a single +hour, and most strongly so in 21 hrs. They re-expanded after three or four +days. +</p> + +<p class="footnote"> +* ‘Leçons’ &c. tom. ii. page 153. [page 117] +</p> + +<p> +The slices were not liquefied, for the walls of the cells, composed of +cellulose, are not in the least acted on by the secretion. +</p> + +<p> +Pollen.—A little fresh pollen from the common pea was placed on the discs +of five leaves, which soon became closely inflected, and remained so for two or +three days. +</p> + +<p> +The grains being then removed, and examined under the microscope, were found +discoloured, with the oil-globules remarkably aggregated. Many had their +contents much shrunk, and some were almost empty. In only a few cases were the +pollen-tubes emitted. There could be no doubt that the secretion had penetrated +the outer coats of the grains, and had partially digested their contents. So it +must be with the gastric juice of the insects which feed on pollen, without +masticating it.* Drosera in a state of nature cannot fail to profit to a +certain extent by this power of digesting pollen, as innumerable grains from +the carices, grasses, rumices, fir-trees, and other wind-fertilised plants, +which commonly grow in the same neighbourhood, will be inevitably caught by the +viscid secretion surrounding the many glands. +</p> + +<p> +Gluten.—This substance is composed of two albuminoids, one soluble, the +other insoluble in alcohol.** Some was prepared by merely washing wheaten flour +in water. A provisional trial was made with rather large pieces placed on two +leaves; these, after 21 hrs., were closely inflected, and remained so for four +days, when one was killed and the other had its glands extremely blackened, but +was not afterwards observed. +</p> + +<p class="footnote"> +* Mr. A.W. Bennett found the undigested coats of the grains in the intestinal +canal of pollen-eating Diptera; see ‘Journal of Hort. Soc. of +London,’ vol. iv. 1874, p. 158. +</p> + +<p class="footnote"> +** Watts’ ‘Dict. of Chemistry,’ vol. ii. 1872, p. 873. [page +118] +</p> + +<p> +Smaller bits were placed on two leaves; these were only slightly inflected in +two days, but afterwards became much more so. Their secretion was not so +strongly acid as that of leaves excited by casein. The bits of gluten, after +lying for three days on the leaves, were more transparent than other bits left +for the same time in water. After seven days both leaves re-expanded, but the +gluten seemed hardly at all reduced in bulk. The glands which had been in +contact with it were extremely black. Still smaller bits of half putrid gluten +were now tried on two leaves; these were well inflected in 24 hrs., and +thoroughly in four days, the glands in contact being much blackened. After five +days one leaf began to re-expand, and after eight days both were fully +re-expanded, some gluten being still left on their discs. Four little chips of +dried gluten, just dipped in water, were next tried, and these acted rather +differently from fresh gluten. One leaf was almost fully re-expanded in three +days, and the other three leaves in four days. The chips were greatly softened, +almost liquefied, but not nearly all dissolved. The glands which had been in +contact with them, instead of being much blackened, were of a very pale colour, +and many of them were evidently killed. +</p> + +<p> +In not one of these ten cases was the whole of the gluten dissolved, even when +very small bits were given. I therefore asked Dr. Burdon Sanderson to try +gluten in artificial digestive fluid of pepsin with hydrochloric acid; and this +dissolved the whole. The gluten, however, was acted on much more slowly than +fibrin; the proportion dissolved within four hours being as 40.8 of gluten to +100 of fibrin. Gluten was also tried in two other digestive fluids, in which +hydrochloric acid was replaced by propionic [page 119] and butyric acids, and +it was completely dissolved by these fluids at the ordinary temperature of a +room. Here, then, at last, we have a case in which it appears that there exists +an essential difference in digestive power between the secretion of Drosera and +gastric juice; the difference being confined to the ferment, for, as we have +just seen, pepsin in combination with acids of the acetic series acts perfectly +on gluten. I believe that the explanation lies simply in the fact that gluten +is too powerful a stimulant (like raw meat, or phosphate of lime, or even too +large a piece of albumen), and that it injures or kills the glands before they +have had time to pour forth a sufficient supply of the proper secretion. That +some matter is absorbed from the gluten, we have clear evidence in the length +of time during which the tentacles remain inflected, and in the greatly changed +colour of the glands. +</p> + +<p> +At the suggestion of Dr. Sanderson, some gluten was left for 15 hrs. in weak +hydrochloric acid (.02 per cent.), in order to remove the starch. It became +colourless, more transparent, and swollen. Small portions were washed and +placed on five leaves, which were soon closely inflected, but to my surprise +re-expanded completely in 48 hrs. A mere vestige of gluten was left on two of +the leaves, and not a vestige on the other three. The viscid and acid +secretion, which remained on the discs of the three latter leaves, was scraped +off and examined by my son under a high power; but nothing could be seen except +a little dirt, and a good many starch grains which had not been dissolved by +the hydrochloric acid. Some of the glands were rather pale. We thus learn that +gluten, treated with weak hydrochloric acid, is not so powerful or so enduring +a [page 120] stimulant as fresh gluten, and does not much injure the glands; +and we further learn that it can be digested quickly and completely by the +secretion. +</p> + +<p> +[Globulin or Crystallin.—This substance was kindly prepared for me from +the lens of the eye by Dr. Moore, and consisted of hard, colourless, +transparent fragments. It is said* that globulin ought to “swell up in +water and dissolve, for the most part forming a gummy liquid;” but this +did not occur with the above fragments, though kept in water for four days. +Particles, some moistened with water, others with weak hydrochloric acid, +others soaked in water for one or two days, were placed on nineteen leaves. +Most of these leaves, especially those with the long soaked particles, became +strongly inflected in a few hours. The greater number re-expanded after three +or four days; but three of the leaves remained inflected during one, two, or +three additional days. Hence some exciting matter must have been absorbed; but +the fragments, though perhaps softened in a greater degree than those kept for +the same time in water, retained all their angles as sharp as ever. As globulin +is an albuminous substance, I was astonished at this result; and my object +being to compare the action of the secretion with that of gastric juice, I +asked Dr. Burdon Sanderson to try some of the globulin used by me. He reports +that “it was subjected to a liquid containing 0.2 per cent. of +hydrochloric acid, and about 1 per cent. of glycerine extract of the stomach of +a dog. It was then ascertained that this liquid was capable of digesting 1.31 +of its weight of unboiled fibrin in 1 hr.; whereas, during the hour, only 0.141 +of the above globulin was dissolved. In both cases an excess of the substance +to be digested was subjected to the liquid.”** We thus see that within +the same time less than one-ninth by weight of globulin than of fibrin was +dissolved; and bearing in mind that pepsin with acids of the acetic series has +only about one-third of the digestive power of pepsin with hydrochloric acid, +it is not surprising that the fragments of +</p> + +<p class="footnote"> +* Watts’ ‘Dictionary of Chemistry,’ vol. ii. page 874. +</p> + +<p class="footnote"> +** I may add that Dr. Sanderson prepared some fresh globulin by Schmidt’s +method, and of this 0.865 was dissolved within the same time, namely, one hour; +so that it was far more soluble than that which I used, though less soluble +than fibrin, of which, as we have seen, 1.31 was dissolved. I wish that I had +tried on Drosera globulin prepared by this method. [page 121] +</p> + +<p> +globulin were not corroded or rounded by the secretion of Drosera, though some +soluble matter was certainly extracted from them and absorbed by the glands. +</p> + +<p> +Haematin.—Some dark red granules, prepared from bullock’s blood, +were given me; these were found by Dr. Sanderson to be insoluble in water, +acids, and alcohol, so that they were probably haematin, together with other +bodies derived from the blood. Particles with little drops of water were placed +on four leaves, three of which were pretty closely inflected in two days; the +fourth only moderately so. On the third day the glands in contact with the +haematin were blackened, and some of the tentacles seemed injured. After five +days two leaves died, and the third was dying; the fourth was beginning to +re-expand, but many of its glands were blackened and injured. It is therefore +clear that matter had been absorbed which was either actually poisonous or of +too stimulating a nature. The particles were much more softened than those kept +for the same time in water, but, judging by the eye, very little reduced in +bulk. Dr. Sanderson tried this substance with artificial digestive fluid, in +the manner described under globulin, and found that whilst 1.31 of fibrin, only +0.456 of the haematin was dissolved in an hour; but the dissolution by the +secretion of even a less amount would account for its action on Drosera. The +residue left by the artificial digestive fluid at first yielded nothing more to +it during several succeeding days.] +</p> + +<p class="center"> +<i>Substances which are not Digested by the Secretion.</i> +</p> + +<p> +All the substances hitherto mentioned cause prolonged inflection of the +tentacles, and are either completely or at least partially dissolved by the +secretion. But there are many other substances, some of them containing +nitrogen, which are not in the least acted on by the secretion, and do not +induce inflection for a longer time than do inorganic and insoluble objects. +These unexciting and indigestible substances are, as far as I have observed, +epidermic productions (such as bits of human nails, balls of hair, the quills +of feathers), fibro-elastic tissue, mucin, pepsin, urea, chitine, chlorophyll, +cellulose, gun-cotton, fat, oil, and starch. [page 122] +</p> + +<p> +To these may be added dissolved sugar and gum, diluted alcohol, and vegetable +infusions not containing albumen, for none of these, as shown in the last +chapter, excite inflection. Now, it is a remarkable fact, which affords +additional and important evidence, that the ferment of Drosera is closely +similar to or identical with pepsin, that none of these same substances are, as +far as it is known, digested by the gastric juice of animals, though some of +them are acted on by the other secretions of the alimentary canal. Nothing more +need be said about some of the above enumerated substances, excepting that they +were repeatedly tried on the leaves of Drosera, and were not in the least +affected by the secretion. About the others it will be advisable to give my +experiments. +</p> + +<p> +[Fibro-elastic Tissue.—We have already seen that when little cubes of +meat, &c., were placed on leaves, the muscles, areolar tissue, and +cartilage were completely dissolved, but the fibro-elastic tissue, even the +most delicate threads, were left without the least signs of having been +attacked. And it is well known that this tissue cannot be digested by the +gastric juice of animals.* +</p> + +<p> +Mucin.—As this substance contains about 7 per cent. of nitrogen, I +expected that it would have excited the leaves greatly and been digested by the +secretion, but in this I was mistaken. From what is stated in chemical works, +it appears extremely doubtful whether mucin can be prepared as a pure +principle. That which I used (prepared by Dr. Moore) was dry and hard. +Particles moistened with water were placed on four leaves, but after two days +there was only a trace of inflection in the immediately adjoining tentacles. +These leaves were then tried with bits of meat, and all four soon became +strongly inflected. Some of the dried mucin was then soaked in water for two +days, and little cubes of the proper size were placed on three leaves. After +four days the tentacles +</p> + +<p class="footnote"> +* See, for instance, Schiff, ‘Phys. de la Digestion,’ 1867, tom. +ii., p. 38. [page 123] +</p> + +<p> +round the margins of the discs were a little inflected, and the secretion +collected on the disc was acid, but the exterior tentacles were not affected. +One leaf began to re-expand on the fourth day, and all were fully re-expanded +on the sixth. The glands which had been in contact with the mucin were a little +darkened. We may therefore conclude that a small amount of some impurity of a +moderately exciting nature had been absorbed. That the mucin employed by me did +contain some soluble matter was proved by Dr. Sanderson, who on subjecting it +to artificial gastric juice found that in 1 hr. some was dissolved, but only in +the proportion of 23 to 100 of fibrin during the same time. The cubes, though +perhaps rather softer than those left in water for the same time, retained +their angles as sharp as ever. We may therefore infer that the mucin itself was +not dissolved or digested. Nor is it digested by the gastric juice of living +animals, and according to Schiff* it is a layer of this substance which +protects the coats of the stomach from being corroded during digestion. +</p> + +<p> +Pepsin.—My experiments are hardly worth giving, as it is scarcely +possible to prepare pepsin free from other albuminoids; but I was curious to +ascertain, as far as that was possible, whether the ferment of the secretion of +Drosera would act on the ferment of the gastric juice of animals. I first used +the common pepsin sold for medicinal purposes, and afterwards some which was +much purer, prepared for me by Dr. Moore. Five leaves to which a considerable +quantity of the former was given remained inflected for five days; four of them +then died, apparently from too great stimulation. I then tried Dr. +Moore’s pepsin, making it into a paste with water, and placing such small +particles on the discs of five leaves that all would have been quickly +dissolved had it been meat or albumen. The leaves were soon inflected; two of +them began to re-expand after only 20 hrs., and the other three were almost +completely re-expanded after 44 hrs. Some of the glands which had been in +contact with the particles of pepsin, or with the acid secretion surrounding +them, were singularly pale, whereas others were singularly dark-coloured. Some +of the secretion was scraped off and examined under a high power; and it +abounded with granules undistinguishable from those of pepsin left in water for +the same length of time. We may therefore infer, as highly probable +(remembering what small quantities were given), that the ferment of Drosera +does not act on or digest +</p> + +<p class="footnote"> +* ‘Leçons phys. de la Digestion,’ 1867, tom. ii., p. 304. [page +124] +</p> + +<p> +pepsin, but absorbs from it some albuminous impurity which induces inflection, +and which in large quantity is highly injurious. Dr. Lauder Brunton at my +request endeavoured to ascertain whether pepsin with hydrochloric acid would +digest pepsin, and as far as he could judge, it had no such power. Gastric +juice, therefore, apparently agrees in this respect with the secretion of +Drosera. +</p> + +<p> +Urea.—It seemed to me an interesting inquiry whether this refuse of the +living body, which contains much nitrogen, would, like so many other animal +fluids and substances, be absorbed by the glands of Drosera and cause +inflection. Half-minim drops of a solution of one part to 437 of water were +placed on the discs of four leaves, each drop containing the quantity usually +employed by me, namely 1/960 of a grain, or .0674 mg.; but the leaves were +hardly at all affected. They were then tested with bits of meat, and soon +became closely inflected. I repeated the same experiment on four leaves with +some fresh urea prepared by Dr. Moore; after two days there was no inflection; +I then gave them another dose, but still there was no inflection. These leaves +were afterwards tested with similarly sized drops of an infusion of raw meat, +and in 6 hrs. there was considerable inflection, which became excessive in 24 +hrs. But the urea apparently was not quite pure, for when four leaves were +immersed in 2 dr. (7.1 ml.) of the solution, so that all the glands, instead of +merely those on the disc, were enabled to absorb any small amount of impurity +in solution, there was considerable inflection after 24 hrs., certainly more +than would have followed from a similar immersion in pure water. That the urea, +which was not perfectly white, should have contained a sufficient quantity of +albuminous matter, or of some salt of ammonia, to have caused the above effect, +is far from surprising, for, as we shall see in the next chapter, astonishingly +small doses of ammonia are highly efficient. We may therefore conclude that +urea itself is not exciting or nutritious to Drosera; nor is it modified by the +secretion, so as to be rendered nutritious, for, had this been the case, all +the leaves with drops on their discs assuredly would have been well inflected. +Dr. Lauder Brunton informs me that from experiments made at my request at St. +Bartholomew’s Hospital it appears that urea is not acted on by artificial +gastric juice, that is by pepsin with hydrochloric acid. +</p> + +<p> +Chitine.—The chitinous coats of insects naturally captured by the leaves +do not appear in the least corroded. Small square pieces of the delicate wing +and of the elytron of a Staphylinus [page 125] were placed on some leaves, and +after these had re-expanded, the pieces were carefully examined. Their angles +were as sharp as ever, and they did not differ in appearance from the other +wing and elytron of the same insect which had been left in water. The elytron, +however, had evidently yielded some nutritious matter, for the leaf remained +clasped over it for four days; whereas the leaves with bits of the true wing +re-expanded on the second day. Any one who will examine the excrement of +insect-eating animals will see how powerless their gastric juice is on chitine. +</p> + +<p> +Cellulose.—I did not obtain this substance in a separate state, but tried +angular bits of dry wood, cork, sphagnum moss, linen, and cotton thread. None +of these bodies were in the least attacked by the secretion, and they caused +only that moderate amount of inflection which is common to all inorganic +objects. Gun-cotton, which consists of cellulose, with the hydrogen replaced by +nitrogen, was tried with the same result. We have seen that a decoction of +cabbage-leaves excites the most powerful inflection. I therefore placed two +little square bits of the blade of a cabbage-leaf, and four little cubes cut +from the midrib, on six leaves of Drosera. These became well inflected in 12 +hrs., and remained so for between two and four days; the bits of cabbage being +bathed all the time by acid secretion. This shows that some exciting matter, to +which I shall presently refer, had been absorbed; but the angles of the squares +and cubes remained as sharp as ever, proving that the framework of cellulose +had not been attacked. Small square bits of spinach-leaves were tried with the +same result; the glands pouring forth a moderate supply of acid secretion, and +the tentacles remaining inflected for three days. We have also seen that the +delicate coats of pollen grains are not dissolved by the secretion. It is well +known that the gastric juice of animals does not attack cellulose. +</p> + +<p> +Chlorophyll.—This substance was tried, as it contains nitrogen. Dr. Moore +sent me some preserved in alcohol; it was dried, but soon deliquesced. +Particles were placed on four leaves; after 3 hrs. the secretion was acid; +after 8 hrs. there was a good deal of inflection, which in 24 hrs. became +fairly well marked. After four days two of the leaves began to open, and the +other two were then almost fully re-expanded. It is therefore clear that this +chlorophyll contained matter which excited the leaves to a moderate degree; but +judging by the eye, little or none was dissolved; so that in a pure state it +would not probably have been attacked by the secretion. Dr. Sanderson tried +that which I [page 126] used, as well as some freshly prepared, with artificial +digestive liquid, and found that it was not digested. Dr. Lauder Brunton +likewise tried some prepared by the process given in the British Pharmacopoeia, +and exposed it for five days at the temperature of 37° Cent. to digestive +liquid, but it was not diminished in bulk, though the fluid acquired a slightly +brown colour. It was also tried with the glycerine extract of pancreas with a +negative result. Nor does chlorophyll seem affected by the intestinal +secretions of various animals, judging by the colour of their excrement. +</p> + +<p> +It must not be supposed from these facts that the grains of chlorophyll, as +they exist in living plants, cannot be attacked by the secretion; for these +grains consist of protoplasm merely coloured by chlorophyll. My son Francis +placed a thin slice of spinach leaf, moistened with saliva, on a leaf of +Drosera, and other slices on damp cotton-wool, all exposed to the same +temperature. After 19 hrs. the slice on the leaf of Drosera was bathed in much +secretion from the inflected tentacles, and was now examined under the +microscope. No perfect grains of chlorophyll could be distinguished; some were +shrunken, of a yellowish-green colour, and collected in the middle of the +cells; others were disintegrated and formed a yellowish mass, likewise in the +middle of the cells. On the other hand, in the slices surrounded by damp +cotton-wool, the grains of chlorophyll were green and as perfect as ever. My +son also placed some slices in artificial gastric juice, and these were acted +on in nearly the same manner as by the secretion. We have seen that bits of +fresh cabbage and spinach leaves cause the tentacles to be inflected and the +glands to pour forth much acid secretion; and there can be little doubt that it +is the protoplasm forming the grains of chlorophyll, as well as that lining the +walls of the cells, which excites the leaves. +</p> + +<p> +Fat and Oil.—Cubes of almost pure uncooked fat, placed on several leaves, +did not have their angles in the least rounded. We have also seen that the +oil-globules in milk are not digested. Nor does olive oil dropped on the discs +of leaves cause any inflection; but when they are immersed in olive oil, they +become strongly inflected; but to this subject I shall have to recur. Oily +substances are not digested by the gastric juice of animals. +</p> + +<p> +Starch.—Rather large bits of dry starch caused well-marked inflection, +and the leaves did not re-expand until the fourth day; but I have no doubt that +this was due to the prolonged irritation of the glands, as the starch continued +to absorb the secretion. The particles were not in the least reduced in size; +[page 127] and we know that leaves immersed in an emulsion of starch are not at +all affected. I need hardly say that starch is not digested by the gastric +juice of animals. +</p> + +<p> +Action of the Secretion on Living Seeds. +</p> + +<p> +The results of some experiments on living seeds, selected by hazard, may here +be given, though they bear only indirectly on our present subject of digestion. +</p> + +<p> +Seven cabbage seeds of the previous year were placed on the same number of +leaves. Some of these leaves were moderately, but the greater number only +slightly inflected, and most of them re-expanded on the third day. One, +however, remained clasped till the fourth, and another till the fifth day. +These leaves therefore were excited somewhat more by the seeds than by +inorganic objects of the same size. After they re-expanded, the seeds were +placed under favourable conditions on damp sand; other seeds of the same lot +being tried at the same time in the same manner, and found to germinate well. +Of the seven seeds which had been exposed to the secretion, only three +germinated; and one of the three seedlings soon perished, the tip of its +radicle being from the first decayed, and the edges of its cotyledons of a dark +brown colour; so that altogether five out of the seven seeds ultimately +perished. +</p> + +<p> +Radish seeds (Raphanus sativus) of the previous year were placed on three +leaves, which became moderately inflected, and re-expanded on the third or +fourth day. Two of these seeds were transferred to damp sand; only one +germinated, and that very slowly. This seedling had an extremely short, +crooked, diseased, radicle, with no absorbent hairs; and the cotyledons were +oddly mottled with purple, with the edges blackened and partly withered. +</p> + +<p> +Cress seeds (Lepidum sativum) of the previous year were placed on four leaves; +two of these next morning were moderately and two strongly inflected, and +remained so for four, five, and even six days. Soon after these seeds were +placed on the leaves and had become damp, they secreted in the usual manner a +layer of tenacious mucus; and to ascertain whether it was the absorption of +this substance by the glands which caused so much inflection, two seeds were +put into water, and as much of the mucus as possible scraped off. They were +then placed on leaves, which became very strongly inflected in the course of 3 +hrs., and were still closely inflected on the third day; so that it evidently +was not the mucus which excited so [page 128] much inflection; on the contrary, +this served to a certain extent as a protection to the seeds. Two of the six +seeds germinated whilst still lying on the leaves, but the seedlings, when +transferred to damp sand, soon died; of the other four seeds, only one +germinated. +</p> + +<p> +Two seeds of mustard (Sinapis nigra), two of celery (Apium +graveolens)—both of the previous year, two seeds well soaked of caraway +(Carum carui), and two of wheat, did not excite the leaves more than inorganic +objects often do. Five seeds, hardly ripe, of a buttercup (Ranunculus), and two +fresh seeds of Anemone nemorosa, induced only a little more effect. On the +other hand, four seeds, perhaps not quite ripe, of Carex sylvatica caused the +leaves on which they were placed to be very strongly inflected; and these only +began to re-expand on the third day, one remaining inflected for seven days. +</p> + +<p> +It follows from these few facts that different kinds of seeds excite the leaves +in very different degrees; whether this is solely due to the nature of their +coats is not clear. In the case of the cress seeds, the partial removal of the +layer of mucus hastened the inflection of the tentacles. Whenever the leaves +remain inflected during several days over seeds, it is clear that they absorb +some matter from them. That the secretion penetrates their coats is also +evident from the large proportion of cabbage, raddish, and cress seeds which +were killed, and from several of the seedlings being greatly injured. This +injury to the seeds and seedlings may, however, be due solely to the acid of +the secretion, and not to any process of digestion; for Mr. Traherne Moggridge +has shown that very weak acids of the acetic series are highly injurious to +seeds. It never occurred to me to observe whether seeds are often blown on to +the viscid leaves of plants growing in a state of nature; but this can hardly +fail sometimes to occur, as we shall hereafter see in the case of Pinguicula. +If so, Drosera will profit to a slight degree by absorbing matter from such +seeds.] +</p> + +<p> +A Summary and Concluding Remarks on the Digestive Power of Drosera. +</p> + +<p> +When the glands on the disc are excited either by the absorption of nitrogenous +matter or by mechanical irritation, their secretion increases in quantity and +becomes acid. They likewise transmit [page 129] some influence to the glands of +the exterior tentacles, causing them to secrete more copiously; and their +secretion likewise becomes acid. With animals, according to Schiff,* mechanical +irritation excites the glands of the stomach to secrete an acid, but not +pepsin. Now, I have every reason to believe (though the fact is not fully +established), that although the glands of Drosera are continually secreting +viscid fluid to replace that lost by evaporation, yet they do not secrete the +ferment proper for digestion when mechanically irritated, but only after +absorbing certain matter, probably of a nitrogenous nature. I infer that this +is the case, as the secretion from a large number of leaves which had been +irritated by particles of glass placed on their discs did not digest albumen; +and more especially from the analogy of Dionaea and Nepenthes. In like manner, +the glands of the stomach of animals secrete pepsin, as Schiff asserts, only +after they have absorbed certain soluble substances, which he designates as +peptogenes. There is, therefore, a remarkable parallelism between the glands of +Drosera and those of the stomach in the secretion of their proper acid and +ferment. +</p> + +<p> +The secretion, as we have seen, completely dissolves albumen, muscle, fibrin, +areolar tissue, cartilage, the fibrous basis of bone, gelatine, chondrin, +casein in the state in which it exists in milk, and gluten which has been +subjected to weak hydrochloric acid. Syntonin and legumin excite the leaves so +powerfully and quickly that there can hardly be a doubt that both would be +dissolved by the secretion. The secretion +</p> + +<p class="footnote"> +* ‘Phys. de la Digestion,’ 1867, tom. ii. pp. 188, 245. [page 130] +</p> + +<p> +failed to digest fresh gluten, apparently from its injuring the glands, though +some was absorbed. Raw meat, unless in very small bits, and large pieces of +albumen, &c., likewise injure the leaves, which seem to suffer, like +animals, from a surfeit. I know not whether the analogy is a real one, but it +is worth notice that a decoction of cabbage leaves is far more exciting and +probably nutritious to Drosera than an infusion made with tepid water; and +boiled cabbages are far more nutritious, at least to man, than the uncooked +leaves. The most striking of all the cases, though not really more remarkable +than many others, is the digestion of so hard and tough a substance as +cartilage. The dissolution of pure phosphate of lime, of bone, dentine, and +especially enamel, seems wonderful; but it depends merely on the long-continued +secretion of an acid; and this is secreted for a longer time under these +circumstances than under any others. It was interesting to observe that as long +as the acid was consumed in dissolving the phosphate of lime, no true digestion +occurred; but that as soon as the bone was completely decalcified, the fibrous +basis was attacked and liquefied with the greatest ease. The twelve substances +above enumerated, which are completely dissolved by the secretion, are likewise +dissolved by the gastric juice of the higher animals; and they are acted on in +the same manner, as shown by the rounding of the angles of albumen, and more +especially by the manner in which the transverse striae of the fibres of muscle +disappear. +</p> + +<p> +The secretion of Drosera and gastric juice were both able to dissolve some +element or impurity out of the globulin and haematin employed by me. The +secretion also dissolved something out of chemically [page 131] prepared +casein, which is said to consist of two substances; and although Schiff asserts +that casein in this state is not attacked by gastric juice, he might easily +have overlooked a minute quantity of some albuminous matter, which Drosera +would detect and absorb. Again, fibro-cartilage, though not properly dissolved, +is acted on in the same manner, both by the secretion of Drosera and gastric +juice. But this substance, as well as the so-called haematin used by me, ought +perhaps to have been classed with indigestible substances. +</p> + +<p> +That gastric juice acts by means of its ferment, pepsin, solely in the presence +of an acid, is well established; and we have excellent evidence that a ferment +is present in the secretion of Drosera, which likewise acts only in the +presence of an acid; for we have seen that when the secretion is neutralised by +minute drops of the solution of an alkali, the digestion of albumen is +completely stopped, and that on the addition of a minute dose of hydrochloric +acid it immediately recommences. +</p> + +<p> +The nine following substances, or classes of substances, namely, epidermic +productions, fibro-elastic tissue, mucin, pepsin, urea, chitine, cellulose, +gun-cotton, chlorophyll, starch, fat and oil, are not acted on by the secretion +of Drosera; nor are they, as far as is known, by the gastric juice of animals. +Some soluble matter, however, was extracted from the mucin, pepsin, and +chlorophyll, used by me, both by the secretion and by artificial gastric juice. +</p> + +<p> +The several substances, which are completely dissolved by the secretion, and +which are afterwards absorbed by the glands, affect the leaves rather +differently. They induce inflection at very different [page 132] rates and in +very different degrees; and the tentacles remain inflected for very different +periods of time. Quick inflection depends partly on the quantity of the +substance given, so that many glands are simultaneously affected, partly on the +facility with which it is penetrated and liquefied by the secretion, partly on +its nature, but chiefly on the presence of exciting matter already in solution. +Thus saliva, or a weak solution of raw meat, acts much more quickly than even a +strong solution of gelatine. So again leaves which have re-expanded, after +absorbing drops of a solution of pure gelatine or isinglass (the latter being +the more powerful of the two), if given bits of meat, are inflected much more +energetically and quickly than they were before, notwithstanding that some rest +is generally requisite between two acts of inflection. We probably see the +influence of texture in gelatine and globulin when softened by having been +soaked in water acting more quickly than when merely wetted. It may be partly +due to changed texture, and partly to changed chemical nature, that albumen, +which had been kept for some time, and gluten which had been subjected to weak +hydrochloric acid, act more quickly than these substances in their fresh state. +</p> + +<p> +The length of time during which the tentacles remain inflected largely depends +on the quantity of the substance given, partly on the facility with which it is +penetrated or acted on by the secretion, and partly on its essential nature. +The tentacles always remain inflected much longer over large bits or large +drops than over small bits or drops. Texture probably plays a part in +determining the extraordinary length of time during which the tentacles remain +inflected [page 133] over the hard grains of chemically prepared casein. But +the tentacles remain inflected for an equally long time over finely powdered, +precipitated phosphate of lime; phosphorus in this latter case evidently being +the attraction, and animal matter in the case of casein. The leaves remain long +inflected over insects, but it is doubtful how far this is due to the +protection afforded by their chitinous integuments; for animal matter is soon +extracted from insects (probably by exosmose from their bodies into the dense +surrounding secretion), as shown by the prompt inflection of the leaves. We see +the influence of the nature of different substances in bits of meat, albumen, +and fresh gluten acting very differently from equal-sized bits of gelatine, +areolar tissue, and the fibrous basis of bone. The former cause not only far +more prompt and energetic, but more prolonged, inflection than do the latter. +Hence we are, I think, justified in believing that gelatine, areolar tissue, +and the fibrous basis of bone, would be far less nutritious to Drosera than +such substances as insects, meat, albumen, &c. This is an interesting +conclusion, as it is known that gelatine affords but little nutriment to +animals; and so, probably, would areolar tissue and the fibrous basis of bone. +The chondrin which I used acted more powerfully than gelatine, but then I do +not know that it was pure. It is a more remarkable fact that fibrin, which +belongs to the great class of Proteids,* including albumen in one of its +sub-groups, does not excite the tentacles in a greater degree, or keep them +inflected for a longer time, than does gelatine, or +</p> + +<p class="footnote"> +* See the classification adopted by Dr. Michael Foster in Watts’ +‘Dictionary of Chemistry,’ Supplement 1872, page 969. [page 134] +</p> + +<p> +areolar tissue, or the fibrous basis of bone. It is not known how long an +animal would survive if fed on fibrin alone, but Dr. Sanderson has no doubt +longer than on gelatine, and it would be hardly rash to predict, judging from +the effects on Drosera, that albumen would be found more nutritious than +fibrin. Globulin likewise belongs to the Proteids, forming another sub-group, +and this substance, though containing some matter which excited Drosera rather +strongly, was hardly attacked by the secretion, and was very little or very +slowly attacked by gastric juice. How far globulin would be nutritious to +animals is not known. We thus see how differently the above specified several +digestible substances act on Drosera; and we may infer, as highly probable, +that they would in like manner be nutritious in very different degrees both to +Drosera and to animals. +</p> + +<p> +The glands of Drosera absorb matter from living seeds, which are injured or +killed by the secretion. They likewise absorb matter from pollen, and from +fresh leaves; and this is notoriously the case with the stomachs of +vegetable-feeding animals. Drosera is properly an insectivorous plant; but as +pollen cannot fail to be often blown on to the glands, as will occasionally the +seeds and leaves of surrounding plants, Drosera is, to a certain extent, a +vegetable-feeder. +</p> + +<p> +Finally, the experiments recorded in this chapter show us that there is a +remarkable accordance in the power of digestion between the gastric juice of +animals with its pepsin and hydrochloric acid and the secretion of Drosera with +its ferment and acid belonging to the acetic series. We can, therefore, hardly +doubt that the ferment in both cases is closely similar, [page 135] if not +identically the same. That a plant and an animal should pour forth the same, or +nearly the same, complex secretion, adapted for the same purpose of digestion, +is a new and wonderful fact in physiology. But I shall have to recur to this +subject in the fifteenth chapter, in my concluding remarks on the Droseraceae. +[page 136] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0007" id="link2HCH0007"></a> +CHAPTER VII.<br/> +THE EFFECTS OF SALTS OF AMMONIA.</h2> + +<p class="letter"> +Manner of performing the experiments—Action of distilled water in +comparison with the solutions—Carbonate of ammonia, absorbed by the +roots—The vapour absorbed by the glands—Drops on the +disc—Minute drops applied to separate glands—Leaves immersed in +weak solutions—Minuteness of the doses which induce aggregation of the +protoplasm—Nitrate of ammonia, analogous experiments with—Phosphate +of ammonia, analogous experiments with—Other salts of +ammonia—Summary and concluding remarks on the action of salts of ammonia. +</p> + +<p> +The chief object in this chapter is to show how powerfully the salts of ammonia +act on the leaves of Drosera, and more especially to show what an +extraordinarily small quantity suffices to excite inflection. I shall, +therefore, be compelled to enter into full details. Doubly distilled water was +always used; and for the more delicate experiments, water which had been +prepared with the utmost possible care was given me by Professor Frankland. The +graduated measures were tested, and found as accurate as such measures can be. +The salts were carefully weighed, and in all the more delicate experiments, by +Borda’s double method. But extreme accuracy would have been superfluous, +as the leaves differ greatly in irritability, according to age, condition, and +constitution. Even the tentacles on the same leaf differ in irritability to a +marked degree. My experiments were tried in the following several ways. +</p> + +<p> +[Firstly.—Drops which were ascertained by repeated trials to be on an +average about half a minim, or the 1/960 of a fluid ounce (.0296 ml.), were +placed by the same pointed instrument on the [page 137] discs of the leaves, +and the inflection of the exterior rows of tentacles observed at successive +intervals of time. It was first ascertained, from between thirty and forty +trials, that distilled water dropped in this manner produces no effect, except +that sometimes, though rarely, two or three tentacles become inflected. In fact +all the many trials with solutions which were so weak as to produce no effect +lead to the same result that water is inefficient. +</p> + +<p> +Secondly.—The head of a small pin, fixed into a handle, was dipped into +the solution under trial. The small drop which adhered to it, and which was +much too small to fall off, was cautiously placed, by the aid of a lens, in +contact with the secretion surrounding the glands of one, two, three, or four +of the exterior tentacles of the same leaf. Great care was taken that the +glands themselves should not be touched. I had supposed that the drops were of +nearly the same size; but on trial this proved a great mistake. I first +measured some water, and removed 300 drops, touching the pin’s head each +time on blotting-paper; and on again measuring the water, a drop was found to +equal on an average about the 1/60 of a minim. Some water in a small vessel was +weighed (and this is a more accurate method), and 300 drops removed as before; +and on again weighing the water, a drop was found to equal on an average only +the 1/89 of a minim. I repeated the operation, but endeavoured this time, by +taking the pin’s head out of the water obliquely and rather quickly, to +remove as large drops as possible; and the result showed that I had succeeded, +for each drop on an average equalled 1/19.4 of a minim. I repeated the +operation in exactly the same manner, and now the drops averaged 1/23.5 of a +minim. Bearing in mind that on these two latter occasions special pains were +taken to remove as large drops as possible, we may safely conclude that the +drops used in my experiments were at least equal to the 1/20 of a minim, or +.0029 ml. One of these drops could be applied to three or even four glands, and +if the tentacles became inflected, some of the solution must have been absorbed +by all; for drops of pure water, applied in the same manner, never produced any +effect. I was able to hold the drop in steady contact with the secretion only +for ten to fifteen seconds; and this was not time enough for the diffusion of +all the salt in solution, as was evident, from three or four tentacles treated +successively with the same drop, often becoming inflected. All the matter in +solution was even then probably not exhausted. +</p> + +<p> +Thirdly.—Leaves cut off and immersed in a measured [page 138] quantity of +the solution under trial; the same number of leaves being immersed at the same +time, in the same quantity of the distilled water which had been used in making +the solution. The leaves in the two lots were compared at short intervals of +time, up to 24 hrs., and sometimes to 48 hrs. They were immersed by being laid +as gently as possible in numbered watch-glasses, and thirty minims (1.775 ml.) +of the solution or of water was poured over each. +</p> + +<p> +Some solutions, for instance that of carbonate of ammonia, quickly discolour +the glands; and as all on the same leaf were discoloured simultaneously, they +must all have absorbed some of the salt within the same short period of time. +This was likewise shown by the simultaneous inflection of the several exterior +rows of tentacles. If we had no such evidence as this, it might have been +supposed that only the glands of the exterior and inflected tentacles had +absorbed the salt; or that only those on the disc had absorbed it, and had then +transmitted a motor impulse to the exterior tentacles; but in this latter case +the exterior tentacles would not have become inflected until some time had +elapsed, instead of within half an hour, or even within a few minutes, as +usually occurred. All the glands on the same leaf are of nearly the same size, +as may best be seen by cutting off a narrow transverse strip, and laying it on +its side; hence their absorbing surfaces are nearly equal. The long-headed +glands on the extreme margin must be excepted, as they are much longer than the +others; but only the upper surface is capable of absorption. Besides the +glands, both surfaces of the leaves and the pedicels of the tentacles bear +numerous minute papillae, which absorb carbonate of ammonia, an infusion of raw +meat, metallic salts, and probably many other substances, but the absorption of +matter by these papillae never induces inflection. We must remember that the +movement of each separate tentacle depends on its gland being excited, except +when a motor impulse is transmitted from the glands of the disc, and then the +movement, as just stated, does not take place until some little time has +elapsed. I have made these remarks because they show us that when a leaf is +immersed in a solution, and the tentacles are inflected, we can judge with some +accuracy how much of the salt each gland has absorbed. For instance, if a leaf +bearing 212 glands be immersed in a measured quantity of a solution, containing +1/10 of a grain of a salt, and all the exterior tentacles, except twelve, are +inflected, we may feel sure that each of the 200 glands can on an average have +absorbed at most 1/2000 of a grain of the salt. I say at [page 139] most, for +the papillae will have absorbed some small amount, and so will perhaps the +glands of the twelve excluded tentacles which did not become inflected. The +application of this principle leads to remarkable conclusions with respect to +the minuteness of the doses causing inflection. +</p> + +<p class="center"> +<i>On the Action of Distilled Water in Causing Inflection.</i> +</p> + +<p> +Although in all the more important experiments the difference between the +leaves simultaneously immersed in water and in the several solutions will be +described, nevertheless it may be well here to give a summary of the effects of +water. The fact, moreover, of pure water acting on the glands deserves in +itself some notice. Leaves to the number of 141 were immersed in water at the +same time with those in the solutions, and their state recorded at short +intervals of time. Thirty-two other leaves were separately observed in water, +making altogether 173 experiments. Many scores of leaves were also immersed in +water at other times, but no exact record of the effects produced was kept; yet +these cursory observations support the conclusions arrived at in this chapter. +A few of the long-headed tentacles, namely from one to about six, were commonly +inflected within half an hour after immersion; as were occasionally a few, and +rarely a considerable number of the exterior round-headed tentacles. After an +immersion of from 5 to 8 hrs. the short tentacles surrounding the outer parts +of the disc generally become inflected, so that their glands form a small dark +ring on the disc; the exterior tentacles not partaking of this movement. Hence, +excepting in a few cases hereafter to be specified, we can judge whether a +solution produces any effect only by observing the exterior tentacles within +the first 3 or 4 hrs. after immersion. +</p> + +<p> +Now for a summary of the state of the 173 leaves after an immersion of 3 or 4 +hrs. in pure water. One leaf had almost all its tentacles inflected; three +leaves had most of them sub-inflected; and thirteen had on an average 36.5 +tentacles inflected. Thus seventeen leaves out of the 173 were acted on in a +marked manner. Eighteen leaves had from seven to nineteen tentacles inflected, +the average being 9.3 tentacles for each leaf. Forty-four leaves had from one +to six tentacles inflected, generally the long-headed ones. So that altogether +of the 173 leaves carefully observed, seventy-nine were affected by the water +in some degree, though commonly to a very slight degree; and ninety-four were +not affected in the least degree. This [page 140] amount of inflection is +utterly insignificant, as we shall hereafter see, compared with that caused by +very weak solutions of several salts of ammonia. +</p> + +<p> +Plants which have lived for some time in a rather high temperature are far more +sensitive to the action of water than those grown out of doors, or recently +brought into a warm greenhouse. Thus in the above seventeen cases, in which the +immersed leaves had a considerable number of tentacles inflected, the plants +had been kept during the winter in a very warm greenhouse; and they bore in the +early spring remarkably fine leaves, of a light red colour. Had I then known +that the sensitiveness of plants was thus increased, perhaps I should not have +used the leaves for my experiments with the very weak solutions of phosphate of +ammonia; but my experiments are not thus vitiated, as I invariably used leaves +from the same plants for simultaneous immersion in water. It often happened +that some leaves on the same plant, and some tentacles on the same leaf, were +more sensitive than others; but why this should be so, I do not know. +</p> + +<p> +FIG. 9. (Drosera rotundifolia.) Leaf (enlarged) with all the tentacles closely +inflected, from immersion in a solution of phosphate of ammonia (one part to +87,500 of water.) +</p> + +<p> +Besides the differences just indicated between the leaves immersed in water and +in weak solutions of ammonia, the tentacles of the latter are in most cases +much more closely inflected. The appearance of a leaf after immersion in a few +drops of a solution of 1 grain of phosphate of ammonia to 200 oz. of water +(i.e. one part to 87,500) is here reproduced: such energetic inflection is +never caused by water alone. With leaves in the weak solutions, the blade or +lamina often becomes inflected; and this is so rare a circumstance with leaves +in water that I have seen only two instances; and in both of these the +inflection was very feeble. Again, with leaves in the weak solutions, the +inflection of the tentacles and blade often goes on steadily, though slowly, +increasing during many hours; and [page 141] this again is so rare a +circumstance with leaves in water that I have seen only three instances of any +such increase after the first 8 to 12 hrs.; and in these three instances the +two outer rows of tentacles were not at all affected. Hence there is sometimes +a much greater difference between the leaves in water and in the weak +solutions, after from 8 hrs. to 24 hrs., than there was within the first 3 +hrs.; though as a general rule it is best to trust to the difference observed +within the shorter time. +</p> + +<p> +With respect to the period of the re-expansion of the leaves, when left +immersed either in water or in the weak solutions, nothing could be more +variable. In both cases the exterior tentacles not rarely begin to re-expand, +after an interval of only from 6 to 8 hrs.; that is just about the time when +the short tentacles round the borders of the disc become inflected. On the +other hand, the tentacles sometimes remain inflected for a whole day, or even +two days; but as a general rule they remain inflected for a longer period in +very weak solutions than in water. In solutions which are not extremely weak, +they never re-expand within nearly so short a period as six or eight hours. +From these statements it might be thought difficult to distinguish between the +effects of water and the weaker solutions; but in truth there is not the +slightest difficulty until excessively weak solutions are tried; and then the +distinction, as might be expected, becomes very doubtful, and at last +disappears. But as in all, except the simplest, cases the state of the leaves +simultaneously immersed for an equal length of time in water and in the +solutions will be described, the reader can judge for himself.] +</p> + +<p class="center"> +C<small>ARBONATE OF</small> A<small>MMONIA</small>. +</p> + +<p> +This salt, when absorbed by the roots, does not cause the tentacles to be +inflected. A plant was so placed in a solution of one part of the carbonate to +146 of water that the young uninjured roots could be observed. The terminal +cells, which were of a pink colour, instantly became colourless, and their +limpid contents cloudy, like a mezzo-tinto engraving, so that some degree of +aggregation was almost instantly caused; but no further change ensued, and the +absorbent hairs were not visibly affected. The tentacles [page 142] did not +bend. Two other plants were placed with their roots surrounded by damp moss, in +half an ounce (14.198 ml.) of a solution of one part of the carbonate to 218 of +water, and were observed for 24 hrs.; but not a single tentacle was inflected. +In order to produce this effect, the carbonate must be absorbed by the glands. +</p> + +<p> +The vapour produces a powerful effect on the glands, and induces inflection. +Three plants with their roots in bottles, so that the surrounding air could not +have become very humid, were placed under a bell-glass (holding 122 fluid +ounces), together with 4 grains of carbonate of ammonia in a watch-glass. After +an interval of 6 hrs. 15 m. the leaves appeared unaffected; but next morning, +after 20 hrs., the blackened glands were secreting copiously, and most of the +tentacles were strongly inflected. These plants soon died. Two other plants +were placed under the same bell-glass, together with half a grain of the +carbonate, the air being rendered as damp as possible; and in 2 hrs. most of +the leaves were affected, many of the glands being blackened and the tentacles +inflected. But it is a curious fact that some of the closely adjoining +tentacles on the same leaf, both on the disc and round the margins, were much, +and some, apparently, not in the least affected. The plants were kept under the +bell-glass for 24 hrs., but no further change ensued. One healthy leaf was +hardly at all affected, though other leaves on the same plant were much +affected. On some leaves all the tentacles on one side, but not those on the +opposite side, were inflected. I doubt whether this extremely unequal action +can be explained by supposing that the more active glands absorb all the vapour +as quickly as it is generated, so that none is left for the others, for we +shall meet with [page 143] analogous cases with air thoroughly permeated with +the vapours of chloroform and ether. +</p> + +<p> +Minute particles of the carbonate were added to the secretion surrounding +several glands. These instantly became black and secreted copiously; but, +except in two instances, when extremely minute particles were given, there was +no inflection. This result is analogous to that which follows from the +immersion of leaves in a strong solution of one part of the carbonate to 109, +or 146, or even 218 of water, for the leaves are then paralysed and no +inflection ensues, though the glands are blackened, and the protoplasm in the +cells of the tentacles undergoes strong aggregation. +</p> + +<p> +[We will now turn to the effects of solutions of the carbonate. Half-minims of +a solution of one part to 437 of water were placed on the discs of twelve +leaves; so that each received 1/960 of a grain or .0675 mg. Ten of these had +their tentacles well inflected; the blades of some being also much curved +inwards. In two cases several of the exterior tentacles were inflected in 35 +m.; but the movement was generally slower. These ten leaves re-expanded in +periods varying between 21 hrs. and 45 hrs., but in one case not until 67 hrs. +had elapsed; so that they re-expanded much more quickly than leaves which have +caught insects. +</p> + +<p> +The same-sized drops of a solution of one part to 875 of water were placed on +the discs of eleven leaves; six remained quite unaffected, whilst five had from +three to six or eight of their exterior tentacles inflected; but this degree of +movement can hardly be considered as trustworthy. Each of these leaves received +1/1920 of a grain (.0337 mg.), distributed between the glands of the disc, but +this was too small an amount to produce any decided effect on the exterior +tentacles, the glands of which had not themselves received any of the salt. +</p> + +<p> +Minute drops on the head of a small pin, of a solution of one part of the +carbonate to 218 of water, were next tried in the manner above described. A +drop of this kind equals on an average 1/20 of a minim, and therefore contains +1/4800 of a grain (.0135 mg.) of the carbonate. I touched with it the viscid +secretion round three glands, so that each gland received only [page 144] +1/14400 of a grain (.00445 mg.). Nevertheless, in two trials all the glands +were plainly blackened; in one case all three tentacles were well inflected +after an interval of 2 hrs. 40 m.; and in another case two of the three +tentacles were inflected. I then tried drops of a weaker solution of one part +to 292 of water on twenty-four glands, always touching the viscid secretion +round three glands with the same little drop. Each gland thus received only the +1/19200 of a grain (.00337 mg.), yet some of them were a little darkened; but +in no one instance were any of the tentacles inflected, though they were +watched for 12 hrs. When a still weaker solution (viz. one part to 437 of +water) was tried on six glands, no effect whatever was perceptible. We thus +learn that the 1/14400 of a grain (.00445 mg.) of carbonate of ammonia, if +absorbed by a gland, suffices to induce inflection in the basal part of the +same tentacle; but as already stated, I was able to hold with a steady hand the +minute drops in contact with the secretion only for a few seconds; and if more +time had been allowed for diffusion and absorption, a much weaker solution +would certainly have acted. +</p> + +<p> +Some experiments were made by immersing cut-off leaves in solutions of +different strengths. Thus four leaves were left for about 3 hrs. each in a +drachm (3.549 ml.) of a solution of one part of the carbonate to 5250 of water; +two of these had almost every tentacle inflected, the third had about half the +tentacles and the fourth about one-third inflected; and all the glands were +blackened. Another leaf was placed in the same quantity of a solution of one +part to 7000 of water, and in 1 hr. 16 m. every single tentacle was well +inflected, and all the glands blackened. Six leaves were immersed, each in +thirty minims (1.774 ml.) of a solution of one part to 4375 of water, and the +glands were all blackened in 31 m. All six leaves exhibited some slight +inflection, and one was strongly inflected. Four leaves were then immersed in +thirty minims of a solution of one part to 8750 of water, so that each leaf +received the 1/320 of a grain (.2025 mg.). Only one became strongly inflected; +but all the glands on all the leaves were of so dark a red after one hour as +almost to deserve to be called black, whereas this did not occur with the +leaves which were at the same time immersed in water; nor did water produce +this effect on any other occasion in nearly so short a time as an hour. These +cases of the simultaneous darkening or blackening of the glands from the action +of weak solutions are important, as they show that all the glands absorbed the +carbonate within the same time, which fact indeed there was not the least +reason to doubt. So again, whenever all the [page 145] tentacles become +inflected within the same time, we have evidence, as before remarked, of +simultaneous absorption. I did not count the number of glands on these four +leaves; but as they were fine ones, and as we know that the average number of +glands on thirty-one leaves was 192, we may safely assume that each bore on an +average at least 170; and if so, each blackened gland could have absorbed only +1/54400 of a grain (.00119 mg.) of the carbonate. +</p> + +<p> +A large number of trials had been previously made with solutions of one part of +the nitrate and phosphate of ammonia to 43750 of water (i.e. one grain to 100 +ounces), and these were found highly efficient. Fourteen leaves were therefore +placed, each in thirty minims of a solution of one part of the carbonate to the +above quantity of water; so that each leaf received 1/1600 of a grain (.0405 +mg.). The glands were not much darkened. Ten of the leaves were not affected, +or only very slightly so. Four, however, were strongly affected; the first +having all the tentacles, except forty, inflected in 47 m.; in 6 hrs. 30 m. all +except eight; and after 4 hrs. the blade itself. The second leaf after 9 m. had +all its tentacles except nine inflected; after 6 hrs. 30 m. these nine were +sub-inflected; the blade having become much inflected in 4 hrs. The third leaf +after 1 hr. 6 m. had all but forty tentacles inflected. The fourth, after 2 +hrs. 5 m., had about half its tentacles and after 4 hrs. all but forty-five +inflected. Leaves which were immersed in water at the same time were not at all +affected, with the exception of one; and this not until 8 hrs. had elapsed. +Hence there can be no doubt that a highly sensitive leaf, if immersed in a +solution, so that all the glands are enabled to absorb, is acted on by 1/1600 +of a grain of the carbonate. Assuming that the leaf, which was a large one, and +which had all its tentacles excepting eight inflected, bore 170 glands, each +gland could have absorbed only 1/268800 of a grain (.00024 mg.); yet this +sufficed to act on each of the 162 tentacles which were inflected. But as only +four out of the above fourteen leaves were plainly affected, this is nearly the +minimum dose which is efficient. +</p> + +<p> +Aggregation of the Protoplasm from the Action of Carbonate of Ammonia.—I +have fully described in the third chapter the remarkable effects of moderately +strong doses of this salt in causing the aggregation of the protoplasm within +the cells of the glands and tentacles; and here my object is merely to show +what small doses suffice. A leaf was immersed in twenty minims (1.183 ml.) of a +solution of one part to 1750 of water, [page 146] and another leaf in the same +quantity of a solution of one part to 3062; in the former case aggregation +occurred in 4 m., in the latter in 11 m. A leaf was then immersed in twenty +minims of a solution of one part to 4375 of water, so that it received 1/240 of +a grain (.27 mg.); in 5 m. there was a slight change of colour in the glands, +and in 15 m. small spheres of protoplasm were formed in the cells beneath the +glands of all the tentacles. In these cases there could not be a shadow of a +doubt about the action of the solution. +</p> + +<p> +A solution was then made of one part to 5250 of water, and I experimented on +fourteen leaves, but will give only a few of the cases. Eight young leaves were +selected and examined with care, and they showed no trace of aggregation. Four +of these were placed in a drachm (3.549 ml.) of distilled water; and four in a +similar vessel, with a drachm of the solution. After a time the leaves were +examined under a high power, being taken alternately from the solution and the +water. The first leaf was taken out of the solution after an immersion of 2 +hrs. 40 m., and the last leaf out of the water after 3 hrs. 50 m.; the +examination lasting for 1 hr. 40 m. In the four leaves out of the water there +was no trace of aggregation except in one specimen, in which a very few, +extremely minute spheres of protoplasm were present beneath some of the round +glands. All the glands were translucent and red. The four leaves which had been +immersed in the solution, besides being inflected, presented a widely different +appearance; for the contents of the cells of every single tentacle on all four +leaves were conspicuously aggregated; the spheres and elongated masses of +protoplasm in many cases extending halfway down the tentacles. All the glands, +both those of the central and exterior tentacles, were opaque and blackened; +and this shows that all had absorbed some of the carbonate. These four leaves +were of very nearly the same size, and the glands were counted on one and found +to be 167. This being the case, and the four leaves having been immersed in a +drachm of the solution, each gland could have received on an average only +1/64128 of a grain (.001009 mg.) of the salt; and this quantity sufficed to +induce within a short time conspicuous aggregation in the cells beneath all the +glands. +</p> + +<p> +A vigorous but rather small red leaf was placed in six minims of the same +solution (viz. one part to 5250 of water), so that it received 1/960 of a grain +(.0675 mg.). In 40 m. the glands appeared rather darker; and in 1 hr. from four +to six spheres of protoplasm were formed in the cells beneath the glands of all +the tentacles. I did not count the tentacles, but we may [page 147] safely +assume that there were at least 140; and if so, each gland could have received +only the 1/134400 of a grain, or .00048 mg. +</p> + +<p> +A weaker solution was then made of one part to 7000 of water, and four leaves +were immersed in it; but I will give only one case. A leaf was placed in ten +minims of this solution; after 1 hr. 37 m. the glands became somewhat darker, +and the cells beneath all of them now contained many spheres of aggregated +protoplasm. This leaf received 1/768 of a grain, and bore 166 glands. Each +gland could, therefore, have received only 1/127488 of a grain (.00507 mg.) of +the carbonate. +</p> + +<p> +Two other experiments are worth giving. A leaf was immersed for 4 hrs. 15 m. in +distilled water, and there was no aggregation; it was then placed for 1 hr. 15 +m. in a little solution of one part to 5250 of water; and this excited +well-marked aggregation and inflection. Another leaf, after having been +immersed for 21 hrs. 15 m. in distilled water, had its glands blackened, but +there was no aggregation in the cells beneath them; it was then left in six +minims of the same solution, and in 1 hr. there was much aggregation in many of +the tentacles; in 2 hrs. all the tentacles (146 in number) were +affected—the aggregation extending down for a length equal to half or the +whole of the glands. It is extremely improbable that these two leaves would +have undergone aggregation if they had been left for a little longer in the +water, namely for 1 hr. and 1 hr. 15 m., during which time they were immersed +in the solution; for the process of aggregation seems invariably to supervene +slowly and very gradually in water.] +</p> + +<p> +A Summary of the Results with Carbonate of Ammonia.—The roots absorb the +solution, as shown by their changed colour, and by the aggregation of the +contents of their cells. The vapour is absorbed by the glands; these are +blackened, and the tentacles are inflected. The glands of the disc, when +excited by a half-minim drop (.0296 ml.), containing 1/960 of a grain (.0675 +mg.), transmit a motor impulse to the exterior tentacles, causing them to bend +inwards. A minute drop, containing 1/14400 of a grain (.00445 mg.), if held for +a few seconds in contact with a gland, soon causes the tentacle bearing it to +be inflected. If a leaf is left [page 148] immersed for a few hours in a +solution, and a gland absorbs the 1/134400 of a grain (.0048 mg.), its colour +becomes darker, though not actually black; and the contents of the cells +beneath the gland are plainly aggregated. Lastly, under the same circumstances, +the absorption by a gland of the 1/268800 of a grain (.00024 mg.) suffices to +excite the tentacle bearing this gland into movement. +</p> + +<p class="center"> +N<small>ITRATE OF</small> A<small>MMONIA</small>. +</p> + +<p> +With the salt I attended only to the inflection of the leaves, for it is far +less efficient than the carbonate in causing aggregation, although considerably +more potent in causing inflection. I experimented with half-minims (.0296 ml.) +on the discs of fifty-two leaves, but will give only a few cases. A solution of +one part to 109 of water was too strong, causing little inflection, and after +24 hrs. killing, or nearly killing, four out of six leaves which were thus +tried; each of which received the 1/240 of a grain (or .27 mg.). A solution of +one part to 218 of water acted most energetically, causing not only the +tentacles of all the leaves, but the blades of some, to be strongly inflected. +Fourteen leaves were tried with drops of a solution of one part to 875 of +water, so that the disc of each received the 1/1920 of a grain (.0337 mg.). Of +these leaves, seven were very strongly acted on, the edges being generally +inflected; two were moderately acted on; and five not at all. I subsequently +tried three of these latter five leaves with urine, saliva, and mucus, but they +were only slightly affected; and this proves that they were not in an active +condition. I mention this fact to show how necessary it is to experiment on +several leaves. Two of the leaves, which were well inflected, re-expanded after +51 hrs. +</p> + +<p> +In the following experiment I happened to select very sensitive leaves. +Half-minims of a solution of one part to 1094 of water (i.e. 1 gr. to 2 1/2 +oz.) were placed on the discs of nine leaves, so that each received the 1/2400 +of a grain (.027 mg.). Three of them had their tentacles strongly inflected and +their blades curled inwards; five were slightly and somewhat doubtfully +affected, having from three to eight of their exterior tentacles inflected: one +leaf was not at all affected, yet was afterwards acted on by saliva. In six of +these cases, a trace of action was perceptible in [page 149] 7 hrs., but the +full effect was not produced until from 24 hrs. to 30 hrs. had elapsed. Two of +the leaves, which were only slightly inflected, re-expanded after an additional +interval of 19 hrs. +</p> + +<p> +Half-minims of a rather weaker solution, viz. of one part to 1312 of water (1 +gr. to 3 oz.) were tried on fourteen leaves; so that each received 1/2880 of a +grain (.0225 mg.), instead of, as in the last experiment, 1/2400 of a grain. +The blade of one was plainly inflected, as were six of the exterior tentacles; +the blade of a second was slightly, and two of the exterior tentacles well, +inflected, all the other tentacles being curled in at right angles to the disc; +three other leaves had from five to eight tentacles inflected; five others only +two or three, and occasionally, though very rarely, drops of pure water cause +this much action; the four remaining leaves were in no way affected, yet three +of them, when subsequently tried with urine, became greatly inflected. In most +of these cases a slight effect was perceptible in from 6 hrs. to 7 hrs., but +the full effect was not produced until from 24 hrs. to 30 hrs. had elapsed. It +is obvious that we have here reached very nearly the minimum amount, which, +distributed between the glands of the disc, acts on the exterior tentacles; +these having themselves not received any of the solution. +</p> + +<p> +In the next place, the viscid secretion round three of the exterior glands was +touched with the same little drop (1/20 of a minim) of a solution of one part +to 437 of water; and after an interval of 2 hrs. 50 m. all three tentacles were +well inflected. Each of these glands could have received only the 1/28800 of a +grain, or .00225 mg. A little drop of the same size and strength was also +applied to four other glands, and in 1 hr. two became inflected, whilst the +other two never moved. We here see, as in the case of the half-minims placed on +the discs, that the nitrate of ammonia is more potent in causing inflection +than the carbonate; for minute drops of the latter salt of this strength +produced no effect. I tried minute drops of a still weaker solution of the +nitrate, viz. one part to 875 of water, on twenty-one glands, but no effect +whatever was produced, except perhaps in one instance. +</p> + +<p> +Sixty-three leaves were immersed in solutions of various strengths; other +leaves being immersed at the same time in the same pure water used in making +the solutions. The results are so remarkable, though less so than with +phosphate of ammonia, that I must describe the experiments in detail, but I +will give only a few. In speaking of the successive periods when inflection +occurred, I always reckon from the time of first immersion. [page 150] +</p> + +<p> +Having made some preliminary trials as a guide, five leaves were placed in the +same little vessel in thirty minims of a solution of one part of the nitrate to +7875 of water (1 gr. to 18 oz.); and this amount of fluid just sufficed to +cover them. After 2 hrs. 10 m. three of the leaves were considerably inflected, +and the other two moderately. The glands of all became of so dark a red as +almost to deserve to be called black. After 8 hrs. four of the leaves had all +their tentacles more or less inflected; whilst the fifth, which I then +perceived to be an old leaf, had only thirty tentacles inflected. Next morning, +after 23 hrs. 40 m., all the leaves were in the same state, excepting that the +old leaf had a few more tentacles inflected. Five leaves which had been placed +at the same time in water were observed at the same intervals of time; after 2 +hrs. 10 m. two of them had four, one had seven, one had ten, of the long-headed +marginal tentacles, and the fifth had four round-headed tentacles, inflected. +After 8 hrs. there was no change in these leaves, and after 24 hrs. all the +marginal tentacles had re-expanded; but in one leaf, a dozen, and in a second +leaf, half a dozen, submarginal tentacles had become inflected. As the glands +of the five leaves in the solution were simultaneously darkened, no doubt they +had all absorbed a nearly equal amount of the salt: and as 1/288 of a grain was +given to the five leaves together, each got 1/1440 of a grain (.045 mg.). I did +not count the tentacles on these leaves, which were moderately fine ones, but +as the average number on thirty-one leaves was 192, it would be safe to assume +that each bore on an average at least 160. If so, each of the darkened glands +could have received only 1/230400 of a grain of the nitrate; and this caused +the inflection of a great majority of the tentacles. +</p> + +<p> +This plan of immersing several leaves in the same vessel is a bad one, as it is +impossible to feel sure that the more vigorous leaves do not rob the weaker +ones of their share of the salt. The glands, moreover, must often touch one +another or the sides of the vessel, and movement may have been thus excited; +but the corresponding leaves in water, which were little inflected, though +rather more so than commonly occurs, were exposed in an almost equal degree to +these same sources of error. I will, therefore, give only one other experiment +made in this manner, though many were tried and all confirmed the foregoing and +following results. Four leaves were placed in forty minims of a solution of one +part to 10,500 of water; and assuming that they absorbed equally, each leaf +received 1/1152 of a grain (.0562 mg.). After 1 hr. 20 m. many of the tentacles +on all four leaves were somewhat inflected. After [page 151] 5 hrs. 30 m. two +leaves had all their tentacles inflected; a third leaf all except the extreme +marginals, which seemed old and torpid; and the fourth a large number. After 21 +hrs. every single tentacle, on all four leaves, was closely inflected. Of the +four leaves placed at the same time in water, one had, after 5 hrs. 45 m., five +marginal tentacles inflected; a second, ten; a third, nine marginals and +submarginals; and the fourth, twelve, chiefly submarginals, inflected. After 21 +hrs. all these marginal tentacles re-expanded, but a few of the submarginals on +two of the leaves remained slightly curved inwards. The contrast was +wonderfully great between these four leaves in water and those in the solution, +the latter having every one of their tentacles closely inflected. Making the +moderate assumption that each of these leaves bore 160 tentacles, each gland +could have absorbed only 1/184320 of a grain (.000351 mg.). This experiment was +repeated on three leaves with the same relative amount of the solution; and +after 6 hrs. 15 m. all the tentacles except nine, on all three leaves taken +together, were closely inflected. In this case the tentacles on each leaf were +counted, and gave an average of 162 per leaf. +</p> + +<p> +The following experiments were tried during the summer of 1873, by placing the +leaves, each in a separate watch-glass and pouring over it thirty minims (1.775 +ml.) of the solution; other leaves being treated in exactly the same manner +with the doubly distilled water used in making the solutions. The trials above +given were made several years before, and when I read over my notes, I could +not believe in the results; so I resolved to begin again with moderately strong +solutions. Six leaves were first immersed, each in thirty minims of a solution +of one part of the nitrate to 8750 of water (1 gr. to 20 oz.), so that each +received 1/320 of a grain (.2025 mg.). Before 30 m. had elapsed, four of these +leaves were immensely, and two of them moderately, inflected. The glands were +rendered of a dark red. The four corresponding leaves in water were not at all +affected until 6 hrs. had elapsed, and then only the short tentacles on the +borders of the disc; and their inflection, as previously explained, is never of +any significance. +</p> + +<p> +Four leaves were immersed, each in thirty minims of a solution of one part to +17,500 of water (1 gr. to 40 oz.), so that each received 1/640 of a grain (.101 +mg.); and in less than 45 m. three of them had all their tentacles, except from +four to ten, inflected; the blade of one being inflected after 6 hrs., and the +blade of a second after 21 hrs. The fourth leaf was not at all affected. The +glands of none were darkened. Of the corresponding leaves [page 152] in water, +only one had any of its exterior tentacles, namely five, inflected; after 6 +hrs. in one case, and after 21 hrs. in two other cases, the short tentacles on +the borders of the disc formed a ring, in the usual manner. +</p> + +<p> +Four leaves were immersed, each in thirty minims of a solution of one part to +43,750 of water (1 gr. to 100 oz.), so that each leaf got 1/1600 of a grain +(.0405 mg.). Of these, one was much inflected in 8 m., and after 2 hrs. 7 m. +had all the tentacles, except thirteen, inflected. The second leaf, after 10 +m., had all except three inflected. The third and fourth were hardly at all +affected, scarcely more than the corresponding leaves in water. Of the latter, +only one was affected, this having two tentacles inflected, with those on the +outer parts of the disc forming a ring in the usual manner. In the leaf which +had all its tentacles except three inflected in 10 m., each gland (assuming +that the leaf bore 160 tentacles) could have absorbed only 1/251200 of a grain, +or .000258 mg. +</p> + +<p> +Four leaves were separately immersed as before in a solution of one part to +131,250 of water (1 gr. to 300 oz.), so that each received 1/4800 of a grain, +or .0135 mg. After 50 m. one leaf had all its tentacles except sixteen, and +after 8 hrs. 20 m. all but fourteen, inflected. The second leaf, after 40 m., +had all but twenty inflected; and after 8 hrs. 10 m. began to re-expand. The +third, in 3 hrs. had about half its tentacles inflected, which began to +re-expand after 8 hrs. 15 m. The fourth leaf, after 3 hrs. 7 m., had only +twenty-nine tentacles more or less inflected. Thus three out of the four leaves +were strongly acted on. It is clear that very sensitive leaves had been +accidentally selected. The day moreover was hot. The four corresponding leaves +in water were likewise acted on rather more than is usual; for after 3 hrs. one +had nine tentacles, another four, and another two, and the fourth none, +inflected. With respect to the leaf of which all the tentacles, except sixteen, +were inflected after 50 m., each gland (assuming that the leaf bore 160 +tentacles) could have absorbed only 1/691200 of a grain (.0000937 mg.), and +this appears to be about the least quantity of the nitrate which suffices to +induce the inflection of a single tentacle. +</p> + +<p> +As negative results are important in confirming the foregoing positive ones, +eight leaves were immersed as before, each in thirty minims of a solution of +one part to 175,000 of water (1 gr. to 400 oz.), so that each received only +1/6400 of a grain (.0101 mg.). This minute quantity produced a slight effect on +only four of the eight leaves. One had fifty-six tentacles inflected after 2 +hrs. 13 m.; a second, twenty-six inflected, or sub-inflected, after [page 153] +38 m.; a third, eighteen inflected, after 1 hr.; and a fourth, ten inflected, +after 35 m. The four other leaves were not in the least affected. Of the eight +corresponding leaves in water, one had, after 2 hrs. 10 m., nine tentacles, and +four others from one to four long-headed tentacles, inflected; the remaining +three being unaffected. Hence, the 1/6400 of a grain given to a sensitive leaf +during warm weather perhaps produces a slight effect; but we must bear in mind +that occasionally water causes as great an amount of inflection as occurred in +this last experiment.] +</p> + +<p> +A Summary of the Results with Nitrate of Ammonia.—The glands of the disc, +when excited by a half-minim drop (.0296 ml.), containing 1/2400 of a grain of +the nitrate (.027 mg.), transmit a motor impulse to the exterior tentacles, +causing them to bend inwards. A minute drop, containing 1/28800 of a grain +(.00225 mg.), if held for a few seconds in contact with a gland, causes the +tentacle bearing this gland to be inflected. If a leaf is left immersed for a +few hours, and sometimes for only a few minutes, in a solution of such strength +that each gland can absorb only the (1/691200 of a grain (.0000937 mg.), this +small amount is enough to excite each tentacle into movement, and it becomes +closely inflected. +</p> + +<p class="center"> +P<small>HOSPHATE OF</small> A<small>MMONIA</small>. +</p> + +<p> +This salt is more powerful than the nitrate, even in a greater degree than the +nitrate is more powerful than the carbonate. This is shown by weaker solutions +of the phosphate acting when dropped on the discs, or applied to the glands of +the exterior tentacles, or when leaves are immersed. The difference in the +power of these three salts, as tried in three different ways, supports the +results presently to be [page 154] given, which are so surprising that their +credibility requires every kind of support. In 1872 I experimented on twelve +immersed leaves, giving each only ten minims of a solution; but this was a bad +method, for so small a quantity hardly covered them. None of these experiments +will, therefore, be given, though they indicate that excessively minute doses +are efficient. When I read over my notes, in 1873, I entirely disbelieved them, +and determined to make another set of experiments with scrupulous care, on the +same plan as those made with the nitrate; namely by placing leaves in +watch-glasses, and pouring over each thirty minims of the solution under trial, +treating at the same time and in the same manner other leaves with the +distilled water used in making the solutions. During 1873, seventy-one leaves +were thus tried in solutions of various strengths, and the same number in +water. Notwithstanding the care taken and the number of the trials made, when +in the following year I looked merely at the results, without reading over my +observations, I again thought that there must have been some error, and +thirty-five fresh trials were made with the weakest solution; but the results +were as plainly marked as before. Altogether, 106 carefully selected leaves +were tried, both in water and in solutions of the phosphate. Hence, after the +most anxious consideration, I can entertain no doubt of the substantial +accuracy of my results. +</p> + +<p> +[Before giving my experiments, it may be well to premise that crystallised +phosphate of ammonia, such as I used, contains 35.33 per cent. of water of +crystallisation; so that in all the following trials the efficient elements +formed only 64.67 per cent. of the salt used. +</p> + +<p> +Extremely minute particles of the dry phosphate were placed [page 155] with the +point of a needle on the secretion surrounding several glands. These poured +forth much secretion, were blackened, and ultimately died; but the tentacles +moved only slightly. The dose, small as it was, evidently was too great, and +the result was the same as with particles of the carbonate of ammonia. +</p> + +<p> +Half-minims of a solution of one part to 437 of water were placed on the discs +of three leaves and acted most energetically, causing the tentacles of one to +be inflected in 15 m., and the blades of all three to be much curved inwards in +2 hrs. 15 m. Similar drops of a solution of one part to 1312 of water, (1 gr. +to 3 oz.) were then placed on the discs of five leaves, so that each received +the 1/2880 of a grain (.0225 mg.). After 8 hrs. the tentacles of four of them +were considerably inflected, and after 24 hrs. the blades of three. After 48 +hrs. all five were almost fully re-expanded. I may mention with respect to one +of these leaves, that a drop of water had been left during the previous 24 hrs. +on its disc, but produced no effect; and that this was hardly dry when the +solution was added. +</p> + +<p> +Similar drops of a solution of one part to 1750 of water (1 gr. to 4 oz.) were +next placed on the discs of six leaves; so that each received 1/3840 of a grain +(.0169 mg.); after 8 hrs. three of them had many tentacles and their blades +inflected; two others had only a few tentacles slightly inflected, and the +sixth was not at all affected. After 24 hrs. most of the leaves had a few more +tentacles inflected, but one had begun to re-expand. We thus see that with the +more sensitive leaves the 1/3840 of a grain, absorbed by the central glands, is +enough to make many of the exterior tentacles and the blades bend, whereas the +1/1920 of a grain of the carbonate similarly given produced no effect; and +1/2880 of a grain of the nitrate was only just sufficient to produce a +well-marked effect. +</p> + +<p> +A minute drop, about equal to 1/20 of a minim, of a solution of one part of the +phosphate to 875 of water, was applied to the secretion on three glands, each +of which thus received only 1/57600 of a grain (.00112 mg.), and all three +tentacles became inflected. Similar drops of a solution of one part to 1312 of +water (1 gr. to 3 oz.) were now tried on three leaves; a drop being applied to +four glands on the same leaf. On the first leaf, three of the tentacles became +slightly inflected in 6 m., and re-expanded after 8 hrs. 45 m. On the second, +two tentacles became sub-inflected in 12 m. And on the third all four tentacles +were decidedly inflected in 12 m.; they remained so for 8 hrs. 30 m., but by +the next morning were fully re-expanded. [page 156] In this latter case each +gland could have received only the 1/115200 (or .000563 mg.) of a grain. +Lastly, similar drops of a solution of one part to 1750 of water (1 gr. to 4 +oz.) were tried on five leaves; a drop being applied to four glands on the same +leaf. The tentacles on three of these leaves were not in the least affected; on +the fourth leaf, two became inflected; whilst on the fifth, which happened to +be a very sensitive one, all four tentacles were plainly inflected in 6 hrs. +15m.; but only one remained inflected after 24 hrs. I should, however, state +that in this case an unusually large drop adhered to the head of the pin. Each +of these glands could have received very little more than 1/153600 of a grain +(or .000423); but this small quantity sufficed to cause inflection. We must +bear in mind that these drops were applied to the viscid secretion for only +from 10 to 15 seconds, and we have good reason to believe that all the +phosphate in the solution would not be diffused and absorbed in this time. We +have seen under the same circumstances that the absorption by a gland of +1/19200 of a grain of the carbonate, and of 1/57600 of a grain of the nitrate, +did not cause the tentacle bearing the gland in question to be inflected; so +that here again the phosphate is much more powerful than the other two salts. +</p> + +<p> +We will now turn to the 106 experiments with immersed leaves. Having +ascertained by repeated trials that moderately strong solutions were highly +efficient, I commenced with sixteen leaves, each placed in thirty minims of a +solution of one part to 43,750 of water (1 gr. to 100 oz.); so that each +received 1/1600 of a grain, or .04058 mg. Of these leaves, eleven had nearly +all or a great number of their tentacles inflected in 1 hr., and the twelfth +leaf in 3 hrs. One of the eleven had every single tentacle closely inflected in +50 m. Two leaves out of the sixteen were only moderately affected, yet more so +than any of those simultaneously immersed in water; and the remaining two, +which were pale leaves, were hardly at all affected. Of the sixteen +corresponding leaves in water, one had nine tentacles, another six, and two +others two tentacles inflected, in the course of 5 hrs. So that the contrast in +appearance between the two lots was extremely great. +</p> + +<p> +Eighteen leaves were immersed, each in thirty minims of a solution of one part +to 87,500 of water (1 gr. to 200 oz.), so that each received 1/3200 of a grain +(.0202 mg.). Fourteen of these were strongly inflected within 2 hrs., and some +of them within 15 m.; three out of the eighteen were only slightly affected, +having twenty-one, nineteen, and twelve tentacles in- [page 157] flected; and +one was not at all acted on. By an accident only fifteen, instead of eighteen, +leaves were immersed at the same time in water; these were observed for 24 +hrs.; one had six, another four, and a third two, of their outer tentacles +inflected; the remainder being quite unaffected. +</p> + +<p> +The next experiment was tried under very favourable circumstances, for the day +(July 8) was very warm, and I happened to have unusually fine leaves. Five were +immersed as before in a solution of one part to 131,250 of water (1 gr. to 300 +oz.), so that each received 1/4800 of a grain, or .0135 mg. After an immersion +of 25 m. all five leaves were much inflected. After 1 hr. 25 m. one leaf had +all but eight tentacles inflected; the second, all but three; the third, all +but five; the fourth; all but twenty-three; the fifth, on the other hand, never +had more than twenty-four inflected. Of the corresponding five leaves in water, +one had seven, a second two, a third ten, a fourth one, and a fifth none +inflected. Let it be observed what a contrast is presented between these latter +leaves and those in the solution. I counted the glands on the second leaf in +the solution, and the number was 217; assuming that the three tentacles which +did not become inflected absorbed nothing, we find that each of the 214 +remaining glands could have absorbed only 1/l027200 of a grain, or .0000631 mg. +The third leaf bore 236 glands, and subtracting the five which did not become +inflected, each of the remaining 231 glands could have absorbed only 1/1108800 +of a grain (or .0000584 mg.), and this amount sufficed to cause the tentacles +to bend. +</p> + +<p> +Twelve leaves were tried as before in a solution of one part to 175,000 of +water (1 gr. to 400 oz.), so that each leaf received 1/6400 of a grain (.0101 +mg.). My plants were not at the time in a good state, and many of the leaves +were young and pale. Nevertheless, two of them had all their tentacles, except +three or four, closely inflected in under 1 hr. Seven were considerably +affected, some within 1 hr., and others not until 3 hrs., 4 hrs. 30 m., and 8 +hrs. had elapsed; and this slow action may be attributed to the leaves being +young and pale. Of these nine leaves, four had their blades well inflected, and +a fifth slightly so. The three remaining leaves were not affected. With respect +to the twelve corresponding leaves in water, not one had its blade inflected; +after from 1 to 2 hrs. one had thirteen of its outer tentacles inflected; a +second six, and four others either one or two inflected. After 8 hrs. the outer +tentacles did not become more inflected; whereas this occurred with the leaves +in the solution. I record in my notes that [page 158] after the 8 hrs. it was +impossible to compare the two lots, and doubt for an instant the power of the +solution. +</p> + +<p> +Two of the above leaves in the solution had all their tentacles, except three +and four, inflected within an hour. I counted their glands, and, on the same +principle as before, each gland on one leaf could have absorbed only 1/1164800, +and on the other leaf only 1/1472000, of a grain of the phosphate. +</p> + +<p> +Twenty leaves were immersed in the usual manner, each in thirty minims of a +solution of one part to 218,750 of water (1 gr. to 500 oz.). So many leaves +were tried because I was then under the false impression that it was incredible +that any weaker solution could produce an effect. Each leaf received 1/8000 of +a grain, or .0081 mg. The first eight leaves which I tried both in the solution +and in water were either young and pale or too old; and the weather was not +hot. They were hardly at all affected; nevertheless, it would be unfair to +exclude them. I then waited until I got eight pairs of fine leaves, and the +weather was favourable; the temperature of the room where the leaves were +immersed varying from 75° to 81° (23°.8 to 27°.2 Cent.) In another trial with +four pairs (included in the above twenty pairs), the temperature in my room was +rather low, about 60° (15°.5 Cent.); but the plants had been kept for several +days in a very warm greenhouse and thus rendered extremely sensitive. Special +precautions were taken for this set of experiments; a chemist weighed for me a +grain in an excellent balance; and fresh water, given me by Prof. Frankland, +was carefully measured. The leaves were selected from a large number of plants +in the following manner: the four finest were immersed in water, and the next +four finest in the solution, and so on till the twenty pairs were complete. The +water specimens were thus a little favoured, but they did not undergo more +inflection than in the previous cases, comparatively with those in the +solution. +</p> + +<p> +Of the twenty leaves in the solution, eleven became inflected within 40 m.; +eight of them plainly and three rather doubtfully; but the latter had at least +twenty of their outer tentacles inflected. Owing to the weakness of the +solution, inflection occurred, except in No. 1, much more slowly than in the +previous trials. The condition of the eleven leaves which were considerably +inflected will now be given at stated intervals, always reckoning from the time +of immersion:— +</p> + +<p> +(1) After only 8 m. a large number of tentacles inflected, and after 17 m. all +but fifteen; after 2 hrs. all but eight in- [page 159] flected, or plainly +sub-inflected. After 4 hrs. the tentacles began to re-expand, and such prompt +re-expansion is unusual; after 7 hrs. 30 m. they were almost fully re-expanded. +</p> + +<p> +(2) After 39 m. a large number of tentacles inflected; after 2 hrs. 18 m. all +but twenty-five inflected; after 4 hrs. 17 m. all but sixteen inflected. The +leaf remained in this state for many hours. +</p> + +<p> +(3) After 12 m. a considerable amount of inflection; after 4 hrs. all the +tentacles inflected except those of the two outer rows, and the leaf remained +in this state for some time; after 23 hrs. began to re-expand. +</p> + +<p> +(4) After 40 m. much inflection; after 4 hrs. 13 m. fully half the tentacles +inflected; after 23 hrs. still slightly inflected. +</p> + +<p> +(5) After 40 m. much inflection; after 4 hrs. 22 m. fully half the tentacles +inflected; after 23 hrs. still slightly inflected. +</p> + +<p> +(6) After 40 m. some inflection; after 2 hrs. 18 m. about twenty-eight outer +tentacles inflected; after 5 hrs. 20 m. about a third of the tentacles +inflected; after 8 hrs. much re-expanded. +</p> + +<p> +(7) After 20 m. some inflection; after 2 hrs. a considerable number of +tentacles inflected; after 7 hrs. 45 m. began to re-expand. +</p> + +<p> +(8) After 38 m. twenty-eight tentacles inflected; after 3 hrs. 45 m. +thirty-three inflected, with most of the submarginal tentacles sub-inflected; +continued so for two days, and then partially re-expanded. +</p> + +<p> +(9) After 38 m. forty-two tentacles inflected; after 3 hrs. 12 m. sixty-six +inflected or sub-inflected; after 6 hrs. 40 m. all but twenty-four inflected or +sub-inflected; after 9 hrs. 40 m. all but seventeen inflected; after 24 hrs. +all but four inflected or sub-inflected, only a few being closely inflected; +after 27 hrs. 40 m. the blade inflected. The leaf remained in this state for +two days, and then began to re-expand. +</p> + +<p> +(10) After 38 m. twenty-one tentacles inflected; after 3 hrs. 12 m. forty-six +tentacles inflected or sub-inflected; after 6 hrs. 40 m. all but seventeen +inflected, though none closely; after 24 hrs. every tentacle slightly curved +inwards; after 27 hrs. 40 m. blade strongly inflected, and so continued for two +days, and then the tentacles and blade very slowly re-expanded. +</p> + +<p> +(11) This fine dark red and rather old leaf, though not very large, bore an +extraordinary number of tentacles (viz. 252), and behaved in an anomalous +manner. After 6 hrs. 40 m. only the short tentacles round the outer part of the +disc were inflected, forming a ring, as so often occurs in from 8 to 24 hrs. +With leaves both in water and the weaker solutions. But after 9 hrs. [page 160] +40 m. all the outer tentacles except twenty-five were inflected; as was the +blade in a strongly marked manner. After 24 hrs. every tentacle except one was +closely inflected, and the blade was completely doubled over. Thus the leaf +remained for two days, when it began to re-expand. I may add that the three +latter leaves (Nos. 9, 10, and 11) were still somewhat inflected after three +days. The tentacles in but few of these eleven leaves became closelyinflected +within so short a time as in the previous experiments with stronger solutions. +</p> + +<p> +We will now turn to the twenty corresponding leaves in water. Nine had none of +their outer tentacles inflected; nine others had from one to three inflected; +and these re-expanded after 8 hrs. The remaining two leaves were moderately +affected; one having six tentacles inflected in 34 m.; the other twenty-three +inflected in 2 hrs. 12 m.; and both thus remained for 24 hrs. None of these +leaves had their blades inflected. So that the contrast between the twenty +leaves in water and the twenty in the solution was very great, both within the +first hour and after from 8 to 12 hrs. had elapsed. +</p> + +<p> +Of the leaves in the solution, the glands on leaf No. 1, which in 2 hrs. had +all its tentacles except eight inflected, were counted and found to be 202. +Subtracting the eight, each gland could have received only the 1/1552000 grain +(.0000411 mg.) of the phosphate. Leaf No. 9 had 213 tentacles, all of which, +with the exception of four, were inflected after 24 hrs., but none of them +closely; the blade was also inflected; each gland could have received only the +1/1672000 of a grain, or .0000387 mg. Lastly, leaf No. 11, which had after 24 +hrs. all its tentacles, except one, closely inflected, as well as the blade, +bore the unusually large number of 252 tentacles; and on the same principle as +before, each gland could have absorbed only the 1/2008000 of a grain, or +.0000322 mg. +</p> + +<p> +With respect to the following experiments, I must premise that the leaves, both +those placed in the solutions and in water, were taken from plants which had +been kept in a very warm greenhouse during the winter. They were thus rendered +extremely sensitive, as was shown by water exciting them much more than in the +previous experiments. Before giving my observations, it may be well to remind +the reader that, judging from thirty-one fine leaves, the average number of +tentacles is 192, and that the outer or exterior ones, the movements of which +are alone significant, are to the short ones on the disc in the proportion of +about sixteen to nine. [page 161] +</p> + +<p> +Four leaves were immersed as before, each in thirty minims of a solution of one +part to 328,125 of water (1 gr. to 750 oz.). Each leaf thus received 1/12000 of +a grain (.0054 mg.) of the salt; and all four were greatly inflected. +</p> + +<p> +(1) After 1 hr. all the outer tentacles but one inflected, and the blade +greatly so; after 7 hrs. began to re-expand. +</p> + +<p> +(2) After 1 hr. all the outer tentacles but eight inflected; after 12 hrs. all +re-expanded. +</p> + +<p> +(3) After 1 hr. much inflection; after 2 hrs. 30 m. all the tentacles but +thirty-six inflected; after 6 hrs. all but twenty-two inflected; after 12 hrs. +partly re-expanded. +</p> + +<p> +(4) After 1 hr. all the tentacles but thirty-two inflected; after 2 hrs. 30 m. +all but twenty-one inflected; after 6 hrs. almost re-expanded. +</p> + +<p> +Of the four corresponding leaves in water:— +</p> + +<p> +(1) After 1 hr. forty-five tentacles inflected; but after 7 hrs. so many had +re-expanded that only ten remained much inflected. +</p> + +<p> +(2) After 1 hr. seven tentacles inflected; these were almost re-expanded in 6 +hrs. +</p> + +<p> +(3) and (4) Not affected, except that, as usual, after 11 hrs. the short +tentacles on the borders of the disc formed a ring. +</p> + +<p> +There can, therefore, be no doubt about the efficiency of the above solution; +and it follows as before that each gland of No. 1 could have absorbed only +1/2412000 of a grain (.0000268 mg.) and of No. 2 only 1/2460000 of a grain +(.0000263 mg.) of the phosphate. +</p> + +<p> +Seven leaves were immersed, each in thirty minims of a solution of one part to +437,500 of water (1 gr. to 1000 oz.). Each leaf thus received 1/16000 of a +grain (.00405 mg.). The day was warm, and the leaves were very fine, so that +all circumstances were favourable. +</p> + +<p> +(1) After 30 m. all the outer tentacles except five inflected, and most of them +closely; after 1 hr. blade slightly inflected; after 9 hrs. 30 m. began to +re-expand. +</p> + +<p> +(2) After 33 m. all the outer tentacles but twenty-five inflected, and blade +slightly so; after 1 hr. 30 m. blade strongly inflected and remained so for 24 +hrs.; but some of the tentacles had then re-expanded. +</p> + +<p> +(3) After 1 hr. all but twelve tentacles inflected; after 2 hrs. 30 m. all but +nine inflected; and of the inflected tentacles all excepting four closely; +blade slightly inflected. After 8 hrs. blade quite doubled up, and now all the +tentacles excepting [page 162] eight closely inflected. The leaf remained in +this state for two days. +</p> + +<p> +(4) After 2 hrs. 20 m. only fifty-nine tentacles inflected; but after 5 hrs. +all the tentacles closely inflected excepting two which were not affected, and +eleven which were only sub-inflected; after 7 hrs. blade considerably +inflected; after 12 hrs. much re-expansion. +</p> + +<p> +(5) After 4 hrs. all the tentacles but fourteen inflected; after 9 hrs. 30 m. +beginning to re-expand. +</p> + +<p> +(6) After 1 hr. thirty-six tentacles inflected; after 5 hrs. all but fifty-four +inflected; after 12 hrs. considerable re-expansion. +</p> + +<p> +(7) After 4 hrs. 30 m. only thirty-five tentacles inflected or sub-inflected, +and this small amount of inflection never increased. +</p> + +<p> +Now for the seven corresponding leaves in water:— +</p> + +<p> +(1) After 4 hrs. thirty-eight tentacles inflected; but after 7 hrs. these, with +the exception of six, re-expanded. +</p> + +<p> +(2) After 4 hrs. 20 m. twenty inflected; these after 9 hrs. partially +re-expanded. +</p> + +<p> +(3) After 4 hrs. five inflected, which began to re-expand after 7 hrs. +</p> + +<p> +(4) After 24 hrs. one inflected. +</p> + +<p> +(5), (6) and (7) Not at all affected, though observed for 24 hrs., excepting +the short tentacles on the borders of the disc, which as usual formed a ring. +</p> + +<p> +A comparison of the leaves in the solution, especially of the first five or +even six on the list, with those in the water, after 1 hr. or after 4 hrs., and +in a still more marked degree after 7 hrs. or 8 hrs., could not leave the least +doubt that the solution had produced a great effect. This was shown not only by +the vastly greater number of inflected tentacles, but by the degree or +closeness of their inflection, and by that of their blades. Yet each gland on +leaf No. 1 (which bore 255 glands, all of which, excepting five, were inflected +in 30 m.) could not have received more than one-four-millionth of a grain +(.0000162 mg.) of the salt. Again, each gland on leaf No. 3 (which bore 233 +glands, all of which, except nine, were inflected in 2 hrs. 30 m.) could have +received at most only the 1/3584000 of a grain, or .0000181 mg. +</p> + +<p> +Four leaves were immersed as before in a solution of one part to 656,250 of +water (1 gr. to 1500 oz.); but on this occasion I happened to select leaves +which were very little sensitive, as on other occasions I chanced to select +unusually sensitive leaves. The leaves were not more affected after 12 hrs. +than [page 163] the four corresponding ones in water; but after 24 hrs. they +were slightly more inflected. Such evidence, however, is not at all +trustworthy. +</p> + +<p> +Twelve leaves were immersed, each in thirty minims of a solution of one part to +1,312,500 of water (1 gr. to 3000 oz.); so that each leaf received 1/48000 of a +grain (.00135 mg.). The leaves were not in very good condition; four of them +were too old and of a dark red colour; four were too pale, yet one of these +latter acted well; the four others, as far as could be told by the eye, seemed +in excellent condition. The result was as follows:— +</p> + +<p> +(1) This was a pale leaf; after 40 m. about thirty-eight tentacles inflected; +after 3 hrs. 30 m. the blade and many of the outer tentacles inflected; after +10 hrs. 15 m. all the tentacles but seventeen inflected, and the blade quite +doubled up; after 24 hrs. all the tentacles but ten more or less inflected. +Most of them were closely inflected, but twenty-five were only sub-inflected. +</p> + +<p> +(2) After 1 hr. 40 m. twenty-five tentacles inflected; after 6 hrs. all but +twenty-one inflected; after 10 hrs. all but sixteen more or less inflected; +after 24 hrs. re-expanded. +</p> + +<p> +(3) After 1 hr. 40 m. thirty-five inflected; after 6 hrs. “a large +number” (to quote my own memorandum) inflected, but from want of time +they were not counted; after 24 hrs. re-expanded. +</p> + +<p> +(4) After 1 hr. 40 m. about thirty inflected; after 6 hrs. “a large +number all round the leaf” inflected, but they were not counted; after 10 +hrs. began to re-expand. +</p> + +<p> +(5) to (12) These were not more inflected than leaves often are in water, +having respectively 16, 8, 10, 8, 4, 9, 14, and 0 tentacles inflected. Two of +these leaves, however, were remarkable from having their blades slightly +inflected after 6 hrs. +</p> + +<p> +With respect to the twelve corresponding leaves in water, (1) had, after 1 hr. +35 m., fifty tentacles inflected, but after 11 hrs. only twenty-two remained +so, and these formed a group, with the blade at this point slightly inflected. +It appeared as if this leaf had been in some manner accidentally excited, for +instance by a particle of animal matter which was dissolved by the water. (2) +After 1 hr. 45 m. thirty-two tentacles inflected, but after 5 hrs. 30 m. only +twenty-five inflected, and these after 10 hrs. all re-expanded; (3) after 1 hr. +twenty-five inflected, which after 10 hrs. 20 m. were all re-expanded; (4) and +(5) after 1 hr. 35 m. six and seven tentacles inflected, which re-expanded +after 11 hrs.; (6), (7) and (8) from one to three inflected, which [page 164] +soon re-expanded; (9), (10), (11) and (12) none inflected, though observed for +twenty-four hours. +</p> + +<p> +Comparing the states of the twelve leaves in water with those in the solution, +there could be no doubt that in the latter a larger number of tentacles were +inflected, and these to a greater degree; but the evidence was by no means so +clear as in the former experiments with stronger solutions. It deserves +attention that the inflection of four of the leaves in the solution went on +increasing during the first 6 hrs., and with some of them for a longer time; +whereas in the water the inflection of the three leaves which were the most +affected, as well as of all the others, began to decrease during this same +interval. It is also remarkable that the blades of three of the leaves in the +solution were slightly inflected, and this is a most rare event with leaves in +water, though it occurred to a slight extent in one (No. 1), which seemed to +have been in some manner accidentally excited. All this shows that the solution +produced some effect, though less and at a much slower rate than in the +previous cases. The small effect produced may, however, be accounted for in +large part by the majority of the leaves having been in a poor condition. +</p> + +<p> +Of the leaves in the solution, No. 1 bore 200 glands and received 1/48000 of a +grain of the salt. Subtracting the seventeen tentacles which were not +inflected, each gland could have absorbed only the 1/8784000 of a grain +(.00000738 mg.). This amount caused the tentacle bearing each gland to be +greatly inflected. The blade was also inflected. +</p> + +<p> +Lastly, eight leaves were immersed, each in thirty minims of a solution of one +part of the phosphate to 21,875,000 of water (1 gr. to 5000 oz.). Each leaf +thus received 1/80000 of a grain of the salt, or .00081 mg. I took especial +pains in selecting the finest leaves from the hot-house for immersion, both in +the solution and the water, and almost all proved extremely sensitive. +Beginning as before with those in the solution:— +</p> + +<p> +(1) After 2 hrs. 30 m. all the tentacles but twenty-two inflected, but some +only sub-inflected; the blade much inflected; after 6 hrs. 30 m. all but +thirteen inflected, with the blade immensely inflected; and remained so for 48 +hrs. +</p> + +<p> +(2) No change for the first 12 hrs., but after 24 hrs. all the tentacles +inflected, excepting those of the outermost row, of which only eleven were +inflected. The inflection continued to increase, and after 48 hrs. all the +tentacles except three were inflected, [page 165] and most of them rather +closely, four or five being only sub-inflected. +</p> + +<p> +(3) No change for the first 12 hrs.; but after 24 hrs. all the tentacles +excepting those of the outermost row were sub-inflected, with the blade +inflected. After 36 hrs. blade strongly inflected, with all the tentacles, +except three, inflected or sub-inflected. After 48 hrs. in the same state. +</p> + +<p> +(4) to (8) These leaves, after 2 hrs. 30 m., had respectively 32, 17, 7, 4, and +0 tentacles inflected, most of which, after a few hours, re-expanded, with the +exception of No. 4, which retained its thirty-two tentacles inflected for 48 +hrs. +</p> + +<p> +Now for the eight corresponding leaves in water:— +</p> + +<p> +(1) After 2 hrs. 40 m. this had twenty of its outer tentacles inflected, five +of which re-expanded after 6 hrs. 30 m. After 10 hrs. 15 m. a most unusual +circumstance occurred, namely, the whole blade became slightly bowed towards +the footstalk, and so remained for 48 hrs. The exterior tentacles, excepting +those of the three or four outermost rows, were now also inflected to an +unusual degree. +</p> + +<p> +(2) to (8) These leaves, after 2 hrs. 40 m., had respectively 42, 12, 9, 8, 2, +1, and 0 tentacles inflected, which all re-expanded within 24 hrs., and most of +them within a much shorter time. +</p> + +<p> +When the two lots of eight leaves in the solution and in the water were +compared after the lapse of 24 hrs., they undoubtedly differed much in +appearance. The few tentacles on the leaves in water which were inflected had +after this interval re-expanded, with the exception of one leaf; and this +presented the very unusual case of the blade being somewhat inflected, though +in a degree hardly approaching that of the two leaves in the solution. Of these +latter leaves, No. 1 had almost all its tentacles, together with its blade, +inflected after an immersion of 2 hrs. 30 m. Leaves No. 2 and 3 were affected +at a much slower rate; but after from 24 hrs. to 48 hrs. almost all their +tentacles were closely inflected, and the blade of one quite doubled up. We +must therefore admit, incredible as the fact may at first appear, that this +extremely weak solution acted on the more sensitive leaves; each of which +received only the 1/80000 of a grain (.00081 mg.) of the phosphate. Now, leaf +No. 3 bore 178 tentacles, and subtracting the three which were not inflected, +each gland could have absorbed only the 1/14000000 of a grain, or .00000463 mg. +Leaf No. 1, which was strongly acted on within 2 hrs. 30 m., and had all its +outer tentacles, except thirteen, inflected within 6 hrs. 30 m., bore 260 +tentacles; and on the same principle as before, each gland could have [page +166] absorbed only 1/19760000 of a grain, or .00000328 mg.; and this +excessively minute amount sufficed to cause all the tentacles bearing these +glands to be greatly inflected. The blade was also inflected.] +</p> + +<p> +A Summary of the Results with Phosphate of Ammonia.—The glands of the +disc, when excited by a half-minim drop (.0296 ml.), containing 1/3840 of a +grain (.0169 mg.) of this salt, transmit a motor impulse to the exterior +tentacles, causing them to bend inwards. A minute drop, containing 1/153600 of +a grain (.000423 mg.), if held for a few seconds in contact with a gland, +causes the tentacle bearing this gland to be inflected. If a leaf is left +immersed for a few hours, and sometimes for a shorter time, in a solution so +weak that each gland can absorb only the 1/9760000 of a grain (.00000328 mg.), +this is enough to excite the tentacle into movement, so that it becomes closely +inflected, as does sometimes the blade. In the general summary to this chapter +a few remarks will be added, showing that the efficiency of such extremely +minute doses is not so incredible as it must at first appear. +</p> + +<p> +[Sulphate of Ammonia.—The few trials made with this and the following +five salts of ammonia were undertaken merely to ascertain whether they induced +inflection. Half-minims of a solution of one part of the sulphate of ammonia to +437 of water were placed on the discs of seven leaves, so that each received +1/960 of a grain, or .0675 mg. After 1 hr. the tentacles of five of them, as +well as the blade of one, were strongly inflected. The leaves were not +afterwards observed. +</p> + +<p> +Citrate of Ammonia.—Half-minims of a solution of one part to 437 of water +were placed on the discs of six leaves. In 1 hr. the short outer tentacles +round the discs were a little inflected, with the glands on the discs +blackened. After 3 hrs. 25 m. one leaf had its blade inflected, but none of the +exterior tentacles. All six leaves remained in nearly the same state during the +day, the submarginal tentacles, however, [page 167] becoming more inflected. +After 23 hrs. three of the leaves had their blades somewhat inflected; and the +submarginal tentacles of all considerably inflected, but in none were the two, +three, or four outer rows affected. I have rarely seen cases like this, except +from the action of a decoction of grass. The glands on the discs of the above +leaves, instead of being almost black, as after the first hour, were now after +23 hrs. very pale. I next tried on four leaves half-minims of a weaker +solution, of one part to 1312 of water (1 gr. to 3 oz.); so that each received +1/2880 of a grain (.0225 mg.). After 2 hrs. 18 m. the glands on the disc were +very dark-coloured; after 24 hrs. two of the leaves were slightly affected; the +other two not at all. +</p> + +<p> +Acetate of Ammonia.—Half-minims of a solution of about one part to 109 of +water were placed on the discs of two leaves, both of which were acted on in 5 +hrs. 30 m., and after 23 hrs. had every single tentacle closely inflected. +</p> + +<p> +Oxalate of Ammonia.—Half-minims of a solution of one part to 218 of water +were placed on two leaves, which, after 7 hrs., became moderately, and after 23 +hrs. strongly, inflected. Two other leaves were tried with a weaker solution of +one part to 437 of water; one was strongly inflected in 7 hrs.; the other not +until 30 hrs. had elapsed. +</p> + +<p> +Tartrate of Ammonia.—Half-minims of a solution of one part to 437 of +water were placed on the discs of five leaves. In 31 m. there was a trace of +inflection in the exterior tentacles of some of the leaves, and this became +more decided after 1 hr. with all the leaves; but the tentacles were never +closely inflected. After 8 hrs. 30 m. they began to re-expand. Next morning, +after 23 hrs., all were fully re-expanded, excepting one which was still +slightly inflected. The shortness of the period of inflection in this and the +following case is remarkable. +</p> + +<p> +Chloride of Ammonium.—Half-minims of a solution of one part to 437 of +water were placed on the discs of six leaves. A decided degree of inflection in +the outer and submarginal tentacles was perceptible in 25 m.; and this +increased during the next three or four hours, but never became strongly +marked. After only 8 hrs. 30 m. the tentacles began to re-expand, and by the +next morning, after 24 hrs., were fully re-expanded on four of the leaves, but +still slightly inflected on two.] +</p> + +<p> +General Summary and Concluding Remarks on the Salts of Ammonia.—We have +now seen that the nine [page 168] salts of ammonia which were tried, all cause +the inflection of the tentacles, and often of the blade of the leaf. As far as +can be ascertained from the superficial trials with the last six salts, the +citrate is the least powerful, and the phosphate certainly by far the most. The +tartrate and chloride are remarkable from the short duration of their action. +The relative efficiency of the carbonate, nitrate, and phosphate, is shown in +the following table by the smallest amount which suffices to cause the +inflection of the tentacles. +</p> + +<p> +Column 1 : Solutions, how applied. Column 2 : Carbonate of Ammonia. Column 3 : +Nitrate of Ammonia. Column 4 : Phosphate of Ammonia. +</p> + +<p> +Placed on the glands of the disc, so as to act indirectly on the outer +tentacles : 1/960 of a grain, or 0675 mg. : 1/2400 of a grain, or .027 mg. : +1/3840 of a grain, or .0169 mg. +</p> + +<p> +Applied for a few seconds directly to the gland of an outer tentacle : 1/14400 +of a grain, or .00445 mg. : 1/28800 of a grain, or .0025 mg. grain, 1/153600 of +a grain, or .000423 mg. +</p> + +<p> +Leaf immersed, with time allowed for each gland to absorb all that it can : +1/268800 of a grain, or .00024 mg. : 1/691200 of a grain, or .0000937 mg. : +1/19760000 of a grain, or .00000328 mg. +</p> + +<p> +Amount absorbed by a gland which suffices to cause the aggregation of the +protoplasm in the adjoining cells of the tentacles. 1/134400 of a grain, or +.00048 mg. +</p> + +<p> +From the experiments tried in these three different ways, we see that the +carbonate, which contains 23.7 per cent. of nitrogen, is less efficient than +the nitrate, which contains 35 per cent. The phosphate contains less nitrogen +than either of these salts, namely, only 21.2 per cent., and yet is far more +[page 169] efficient; its power no doubt depending quite as much on the +phosphorus as on the nitrogen which it contains. We may infer that this is the +case, from the energetic manner in which bits of bone and phosphate of lime +affect the leaves. The inflection excited by the other salts of ammonia is +probably due solely to their nitrogen,—on the same principle that +nitrogenous organic fluids act powerfully, whilst non-nitrogenous organic +fluids are powerless. As such minute doses of the salts of ammonia affect the +leaves, we may feel almost sure that Drosera absorbs and profits by the amount, +though small, which is present in rain-water, in the same manner as other +plants absorb these same salts by their roots. +</p> + +<p> +The smallness of the doses of the nitrate, and more especially of the phosphate +of ammonia, which cause the tentacles of immersed leaves to be inflected, is +perhaps the most remarkable fact recorded in this volume. When we see that much +less than the millionth* of a grain of the phosphate, absorbed by a gland of +one of the exterior tentacles, causes it to bend, it may be thought that the +effects of the solution on the glands of the disc have been overlooked; namely, +the transmission of a motor impulse from them to the exterior tentacles. No +doubt the movements of the latter are thus aided; but the aid thus rendered +must be insignificant; for we know that a drop containing as much as the 1/3840 +of a grain placed on the disc is only just able to cause the outer tentacles of +a highly sensitive leaf to bend. It is cer- +</p> + +<p class="footnote"> +* It is scarcely possible to realise what a million means. The best +illustration which I have met with is that given by Mr. Croll, who +says,—Take a narrow strip of paper 83 ft. 4 in. in length, and stretch it +along the wall of a large hall; then mark off at one end the tenth of an inch. +This tenth will represent a hundred, and the entire strip a million. [page 170] +</p> + +<p> +tainly a most surprising fact that the 1/19760000 of a grain, or in round +numbers the one-twenty-millionth of a grain (.0000033 mg.), of the phosphate +should affect any plant, or indeed any animal; and as this salt contains 35.33 +per cent. of water of crystallisation, the efficient elements are reduced to +1/30555126 of a grain, or in round numbers to one-thirty-millionth of a grain +(.00000216 mg.). The solution, moreover, in these experiments was diluted in +the proportion of one part of the salt to 2,187,500 of water, or one grain to +5000 oz. The reader will perhaps best realise this degree of dilution by +remembering that 5000 oz. would more than fill a 31-gallon cask; and that to +this large body of water one grain of the salt was added; only half a drachm, +or thirty minims, of the solution being poured over a leaf. Yet this amount +sufficed to cause the inflection of almost every tentacle, and often of the +blade of the leaf. +</p> + +<p> +I am well aware that this statement will at first appear incredible to almost +everyone. Drosera is far from rivalling the power of the spectroscope, but it +can detect, as shown by the movements of its leaves, a very much smaller +quantity of the phosphate of ammonia than the most skilful chemist can of any +substance.* My results were for a long time incredible +</p> + +<p class="footnote"> +* When my first observations were made on the nitrate of ammonia, fourteen +years ago, the powers of the spectroscope had not been discovered; and I felt +all the greater interest in the then unrivalled powers of Drosera. Now the +spectroscope has altogether beaten Drosera; for according to Bunsen and +Kirchhoff probably less than one 1/200000000 of a grain of sodium can be thus +detected (see Balfour Stewart, ‘Treatise on Heat,’ 2nd edit. 1871, +p. 228). With respect to ordinary chemical tests, I gather from Dr. Alfred +Taylor’s work on ‘Poisons’ that about 1/4000 of a grain of +arsenic, 1/4400 of a grain of prussic acid, 1/1400 of iodine, and 1/2000 of +tartarised antimony, can be detected; but the power of detection depends much +on the solutions under trial not being extremely weak. [page 171] +</p> + +<p> +even to myself, and I anxiously sought for every source of error. The salt was +in some cases weighed for me by a chemist in an excellent balance; and fresh +water was measured many times with care. The observations were repeated during +several years. Two of my sons, who were as incredulous as myself, compared +several lots of leaves simultaneously immersed in the weaker solutions and in +water, and declared that there could be no doubt about the difference in their +appearance. I hope that some one may hereafter be induced to repeat my +experiments; in this case he should select young and vigorous leaves, with the +glands surrounded by abundant secretion. The leaves should be carefully cut off +and laid gently in watch-glasses, and a measured quantity of the solution and +of water poured over each. The water used must be as absolutely pure as it can +be made. It is to be especially observed that the experiments with the weaker +solutions ought to be tried after several days of very warm weather. Those with +the weakest solutions should be made on plants which have been kept for a +considerable time in a warm greenhouse, or cool hothouse; but this is by no +means necessary for trials with solutions of moderate strength. +</p> + +<p> +I beg the reader to observe that the sensitiveness or irritability of the +tentacles was ascertained by three different methods—indirectly by drops +placed on the disc, directly by drops applied to the glands of the outer +tentacles, and by the immersion of whole leaves; and it was found by these +three methods that the nitrate was more powerful than the carbonate, and the +phosphate much more powerful than the nitrate; this result being intelligible +from the difference in the amount of nitrogen in the first two salts, and from +the presence of phosphorus in the third. It may aid the [page 172] +reader’s faith to turn to the experiments with a solution of one grain of +the phosphate to 1000 oz. of water, and he will there find decisive evidence +that the one-four-millionth of a grain is sufficient to cause the inflection of +a single tentacle. There is, therefore, nothing very improbable in the fifth of +this weight, or the one-twenty-millionth of a grain, acting on the tentacle of +a highly sensitive leaf. Again, two of the leaves in the solution of one grain +to 3000 oz., and three of the leaves in the solution of one grain to 5000 oz., +were affected, not only far more than the leaves tried at the same time in +water, but incomparably more than any five leaves which can be picked out of +the 173 observed by me at different times in water. +</p> + +<p> +There is nothing remarkable in the mere fact of the one-twenty-millionth of a +grain of the phosphate, dissolved in above two-million times its weight of +water, being absorbed by a gland. All physiologists admit that the roots of +plants absorb the salts of ammonia brought to them by the rain; and fourteen +gallons of rain-water contain* a grain of ammonia, therefore only a little more +than twice as much as in the weakest solution employed by me. The fact which +appears truly wonderful is, that the one-twenty-millionth of a grain of the +phosphate of ammonia (including less than the one-thirty-millionth of efficient +matter), when absorbed by a gland, should induce some change in it, which leads +to a motor impulse being transmitted down the whole length of the tentacle, +causing the basal part to bend, often through an angle of above 180 degrees. +</p> + +<p> +Astonishing as is this result, there is no sound reason +</p> + +<p class="footnote"> +* Miller’s ‘Elements of Chemistry,’ part ii. p. 107, 3rd +edit. 1864. [page 173] +</p> + +<p> +why we should reject it as incredible. Prof. Donders, of Utrecht, informs me +that from experiments formerly made by him and Dr. De Ruyter, he inferred that +less than the one-millionth of a grain of sulphate of atropine, in an extremely +diluted state, if applied directly to the iris of a dog, paralyses the muscles +of this organ. But, in fact, every time that we perceive an odour, we have +evidence that infinitely smaller particles act on our nerves. When a dog stands +a quarter of a mile to leeward of a deer or other animal, and perceives its +presence, the odorous particles produce some change in the olfactory nerves; +yet these particles must be infinitely smaller* than those of the phosphate of +ammonia weighing the one-twenty-millionth of a grain. These nerves then +transmit some influence to the brain of the dog, which leads to action on its +part. With Drosera, the really marvellous fact is, that a plant without any +specialised nervous system should be affected by such minute particles; but we +have no grounds for assuming that other tissues could not be rendered as +exquisitely susceptible to impressions from without if this were beneficial to +the organism, as is the nervous system of the higher animals. +</p> + +<p class="footnote"> +* My son, George Darwin, has calculated for me the diameter of a sphere of +phosphate of ammonia (specific gravity 1.678), weighing the +one-twenty-millionth of a grain, and finds it to be 1/1644 of an inch. Now, Dr. +Klein informs me that the smallest Micrococci, which are distinctly discernible +under a power of 800 diameters, are estimated to be from .0002 to .0005 of a +millimetre—that is, from 1/50800 to 1/127000 of an inch—in +diameter. Therefore, an object between 1/31 and 1/77 of the size of a sphere of +the phosphate of ammonia of the above weight can be seen under a high power; +and no one supposes that odorous particles, such as those emitted from the deer +in the above illustration, could be seen under any power of the microscope.) +[page 174] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0008" id="link2HCH0008"></a> +CHAPTER VIII.<br/> +THE EFFECTS OF VARIOUS OTHER SALTS AND ACIDS ON THE LEAVES.</h2> + +<p class="letter"> +Salts of sodium, potassium, and other alkaline, earthy, and metallic +salts—Summary on the action of these salts—Various +acids—Summary on their action. +</p> + +<p> +Having found that the salts of ammonia were so powerful, I was led to +investigate the action of some other salts. It will be convenient, first, to +give a list of the substances tried (including forty-nine salts and two +metallic acids), divided into two columns, showing those which cause +inflection, and those which do not do so, or only doubtfully. My experiments +were made by placing half-minim drops on the discs of leaves, or, more +commonly, by immersing them in the solutions; and sometimes by both methods. A +summary of the results, with some concluding remarks, will then be given. The +action of various acids will afterwards be described. +</p> + +<p> +COLUMN 1 : SALTS CAUSING INFLECTION. COLUMN 2 : SALTS NOT CAUSING INFLECTION. +</p> + +<p> +(Arranged in Groups according to the Chemical Classification in Watts’ +‘Dictionary of Chemistry.’) +</p> + +<p> +Sodium carbonate, rapid inflection. : Potassium carbonate: slowly poisonous. +Sodium nitrate, rapid inflection. : Potassium nitrate: somewhat poisonous. +Sodium sulphate, moderately rapid inflection. : Potassium sulphate. Sodium +phosphate, very rapid inflection. : Potassium phosphate. Sodium citrate, rapid +inflection. : Potassium citrate. Sodium oxalate; rapid inflection. Sodium +chloride, moderately rapid inflection. : Potassium chloride. [page 175] +</p> + +<p> +COLUMN 1 : SALTS CAUSING INFLECTION. COLUMN 2 : SALTS NOT CAUSING INFLECTION. +</p> + +<p> +(Arranged in Groups according to the Chemical Classification in Watts’ +‘Dictionary of Chemistry.’) +</p> + +<p class="letter"> +Sodium iodide, rather slow inflection. : Potassium iodide, a slight and +doubtful amount of inflection. Sodium bromide, moderately rapid inflection. : +Potassium bromide. Potassium oxalate, slow and doubtful inflection. : Lithium +nitrate, moderately rapid inflection. : Lithium acetate. Caesium chloride, +rather slow inflection. : Rubidium chloride. Silver nitrate, rapid inflection: +quick poison. : Cadmium chloride, slow inflection. : Calcium acetate. Mercury +perchloride, rapid inflection: quick poison. : Calcium nitrate. : Magnesium +acetate. : Magnesium nitrate. : Magnesium chloride. : Magnesium sulphate. : +Barium acetate. : Barium nitrate. : Strontium acetate. : Strontium nitrate. : +Zinc chloride. +</p> + +<p> +Aluminium chloride, slow and doubtful inflection. : Aluminium nitrate, a trace +of inflection. Gold chloride, rapid inflection: quick poison. : Aluminium and +potassium sulphate. +</p> + +<p> +Tin chloride, slow inflection: poisonous. : Lead chloride. +</p> + +<p> +Antimony tartrate, slow inflection: probably poisonous. Arsenious acid, quick +inflection: poisonous. Iron chloride, slow inflection: probably poisonous. : +Manganese chloride. Chromic acid, quick inflection: highly poisonous. Copper +chloride, rather slow in flection: poisonous. : Cobalt chloride. Nickel +chloride, rapid inflection: probably poisonous. Platinum chloride, rapid +inflection: poisonous. [page 176] +</p> + +<p> +Sodium, Carbonate of (pure, given me by Prof. Hoffmann).—Half-minims +(.0296 ml.) of a solution of one part to 218 of water (2 grs. to 1 oz.) were +placed on the discs of twelve leaves. Seven of these became well inflected; +three had only two or three of their outer tentacles inflected, and the +remaining two were quite unaffected. But the dose, though only the 1/480 of a +grain (.135 mg.), was evidently too strong, for three of the seven +well-inflected leaves were killed. On the other hand, one of the seven, which +had only a few tentacles inflected, re-expanded and seemed quite healthy after +48 hrs. By employing a weaker solution (viz. one part to 437 of water, or 1 gr. +to 1 oz.), doses of 1/960 of a grain (.0675 mg.) were given to six leaves. Some +of these were affected in 37 m.; and in 8 hrs. the outer tentacles of all, as +well as the blades of two, were considerably inflected. After 23 hrs. 15 m. the +tentacles had almost re-expanded, but the blades of the two were still just +perceptibly curved inwards. After 48 hrs. all six leaves were fully +re-expanded, and appeared perfectly healthy. +</p> + +<p> +Three leaves were immersed, each in thirty minims of a solution of one part to +875 of water (1 gr. to 2 oz.), so that each received 1/32 of a grain (2.02 +mg.); after 40 m. the three were much affected, and after 6 hrs. 45 m. the +tentacles of all and the blade of one closely inflected. +</p> + +<p> +Sodium, Nitrate of (pure).—Half-minims of a solution of one part to 437 +of water, containing 1/960 of a grain (.0675 mg.), were placed on the discs of +five leaves. After 1 hr. 25 m. the tentacles of nearly all, and the blade of +one, were somewhat inflected. The inflection continued to increase, and in 21 +hrs. 15 m. the tentacles and the blades of four of them were greatly affected, +and the blade of the fifth to a slight extent. After an additional 24 hrs. the +four leaves still remained closely inflected, whilst the fifth was beginning to +expand. Four days after the solution had been applied, two of the leaves had +quite, and one had partially, re-expanded; whilst the remaining two remained +closely inflected and appeared injured. +</p> + +<p> +Three leaves were immersed, each in thirty minims of a solution of one part to +875 of water; in 1 hr. there was great inflection, and after 8 hrs. 15 m. every +tentacle and the blades of all three were most strongly inflected. +</p> + +<p> +Sodium, Sulphate of.—Half-minims of a solution of one part to 437 of +water were placed on the discs of six leaves. After 5 hrs. 30 m. the tentacles +of three of them, (with the blade of one) were considerably; and those of the +other three slightly, inflected. After 21 hrs. the inflection had a little +decreased, [page 177] and in 45 hrs. the leaves were fully expanded, appearing +quite healthy. +</p> + +<p> +Three leaves were immersed, each in thirty minims of a solution of one part of +the sulphate to 875 of water; after 1 hr. 30 m. there was some inflection, +which increased so much that in 8 hrs. 10 m. all the tentacles and the blades +of all three leaves were closely inflected. +</p> + +<p> +Sodium, Phosphate of.—Half-minims of a solution of one part to 437 of +water were placed on the discs of six leaves. The solution acted with +extraordinary rapidity, for in 8 m. the outer tentacles on several of the +leaves were much incurved. After 6 hrs. the tentacles of all six leaves, and +the blades of two, were closely inflected. This state of things continued for +24 hrs., excepting that the blade of a third leaf became incurved. After 48 +hrs. all the leaves re-expanded. It is clear that 1/960 of a grain of phosphate +of soda has great power in causing inflection. +</p> + +<p> +Sodium, Citrate of.—Half-minims of a solution of one part to 437 of water +were placed on the discs of six leaves, but these were not observed until 22 +hrs. had elapsed. The sub-marginal tentacles of five of them, and the blades of +four, were then found inflected; but the outer rows of tentacles were not +affected. One leaf, which appeared older than the others, was very little +affected in any way. After 46 hrs. four of the leaves were almost re-expanded, +including their blades. Three leaves were also immersed, each in thirty minims +of a solution of one part of the citrate to 875 of water; they were much acted +on in 25 m.; and after 6 hrs. 35 m. almost all the tentacles, including those +of the outer rows, were inflected, but not the blades. +</p> + +<p> +Sodium, Oxalate of.—Half-minims of a solution of one part to 437 of water +were placed on the discs of seven leaves; after 5 hrs. 30 m. the tentacles of +all, and the blades of most of them, were much affected. In 22 hrs., besides +the inflection of the tentacles, the blades of all seven leaves were so much +doubled over that their tips and bases almost touched. On no other occasion +have I seen the blades so strongly affected. Three leaves were also immersed, +each in thirty minims of a solution of one part to 875 of water; after 30 m. +there was much inflection, and after 6 hrs. 35 m. the blades of two and the +tentacles of all were closely inflected. +</p> + +<p> +Sodium, Chloride of (best culinary salt).—Half-minims of a solution of +one part to 218 of water were placed on the discs [page 178] of four leaves. +Two, apparently, were not at all affected in 48 hrs.; the third had its +tentacles slightly inflected; whilst the fourth had almost all its tentacles +inflected in 24 hrs., and these did not begin to re-expand until the fourth +day, and were not perfectly expanded on the seventh day. I presume that this +leaf was injured by the salt. Half-minims of a weaker solution, of one part to +437 of water, were then dropped on the discs of six leaves, so that each +received 1/960 of a grain. In 1 hr. 33 m. there was slight inflection; and +after 5 hrs. 30 m. the tentacles of all six leaves were considerably, but not +closely, inflected. After 23 hrs. 15 m. all had completely re-expanded, and did +not appear in the least injured. +</p> + +<p> +Three leaves were immersed, each in thirty minims of a solution of one part to +875 of water, so that each received 1/32 of a grain, or 2.02 mg. After 1 hr. +there was much inflection; after 8 hrs. 30 m. all the tentacles and the blades +of all three were closely inflected. Four other leaves were also immersed in +the solution, each receiving the same amount of salt as before, viz. 1/32 of a +grain. They all soon became inflected; after 48 hrs. they began to re-expand, +and appeared quite uninjured, though the solution was sufficiently strong to +taste saline. +</p> + +<p> +Sodium, Iodide of.—Half-minims of a solution of one part to 437 of water +were placed on the discs of six leaves. After 24 hrs. four of them had their +blades and many tentacles inflected. The other two had only their submarginal +tentacles inflected; the outer ones in most of the leaves being but little +affected. After 46 hrs. the leaves had nearly re-expanded. Three leaves were +also immersed, each in thirty minims of a solution of one part to 875 of water. +After 6 hrs. 30 m. almost all the tentacles, and the blade of one leaf, were +closely inflected. +</p> + +<p> +Sodium, Bromide of.—Half-minims of a solution of one part to 437 of water +were placed on six leaves. After 7 hrs. there was some inflection; after 22 +hrs. three of the leaves had their blades and most of their tentacles +inflected; the fourth leaf was very slightly, and the fifth and sixth hardly at +all, affected. Three leaves were also immersed, each in thirty minims of a +solution of one part to 875 of water; after 40 m. there was some inflection; +after 4 hrs. the tentacles of all three leaves and the blades of two were +inflected. These leaves were then placed in water, and after 17 hrs. 30 m. two +of them were almost completely, and the third partially, re-expanded; so that +apparently they were not injured. [page 179] +</p> + +<p> +Potassium, Carbonate of (pure).—Half-minims of a solution of one part to +437 of water were placed on six leaves. No effect was produced in 24 hrs.; but +after 48 hrs. some of the leaves had their tentacles, and one the blade, +considerably inflected. This, however, seemed the result of their being +injured; for on the third day after the solution was given, three of the leaves +were dead, and one was very unhealthy; the other two were recovering, but with +several of their tentacles apparently injured, and these remained permanently +inflected. It is evident that the 1/960 of a grain of this salt acts as a +poison. Three leaves were also immersed, each in thirty minims of a solution of +one part to 875 of water, though only for 9 hrs.; and, very differently from +what occurs with the salts of soda, no inflection ensued. +</p> + +<p> +Potassium, Nitrate of.—Half-minims of a strong solution, of one part to +109 of water (4 grs. to 1 oz.), were placed on the discs of four leaves; two +were much injured, but no inflection ensued. Eight leaves were treated in the +same manner, with drops of a weaker solution, of one part to 218 of water. +After 50 hrs. there was no inflection, but two of the leaves seemed injured. +Five of these leaves were subsequently tested with drops of milk and a solution +of gelatine on their discs, and only one became inflected; so that the solution +of the nitrate of the above strength, acting for 50 hrs., apparently had +injured or paralysed the leaves. Six leaves were then treated in the same +manner with a still weaker solution, of one part to 437 of water, and these, +after 48 hrs., were in no way affected, with the exception of perhaps a single +leaf. Three leaves were next immersed for 25 hrs., each in thirty minims of a +solution of one part to 875 of water, and this produced no apparent effect. +They were then put into a solution of one part of carbonate of ammonia to 218 +of water; the glands were immediately blackened, and after 1 hr. there was some +inflection, and the protoplasmic contents of the cells became plainly +aggregated. This shows that the leaves had not been much injured by their +immersion for 25 hrs. in the nitrate. +</p> + +<p> +Potassium, Sulphate of.—Half-minims of a solution of one part to 437 of +water were placed on the discs of six leaves. After 20 hrs. 30 m. no effect was +produced; after an additional 24 hrs. three remained quite unaffected; two +seemed injured, and the sixth seemed almost dead with its tentacles inflected. +Nevertheless, after two additional days, all six leaves recovered. The +immersion of three leaves for 24 hrs., each in thirty minims of [page 180] a +solution of one part to 875 of water, produced no apparent effect. They were +then treated with the same solution of carbonate of ammonia, with the same +result as in the case of the nitrate of potash. +</p> + +<p> +Potassium, Phosphate of.—Half-minims of a solution of one part to 437 of +water were placed on the discs of six leaves, which were observed during three +days; but no effect was produced. The partial drying up of the fluid on the +disc slightly drew together the tentacles on it, as often occurs in experiments +of this kind. The leaves on the third day appeared quite healthy. +</p> + +<p> +Potassium, Citrate of.—Half-minims of a solution of one part to 437 of +water, left on the discs of six leaves for three days, and the immersion of +three leaves for 9 hrs., each in 30 minims of a solution of one part to 875 of +water, did not produce the least effect. +</p> + +<p> +Potassium, Oxalate of.—Half-minims were placed on different occasions on +the discs of seventeen leaves; and the results perplexed me much, as they still +do. Inflection supervened very slowly. After 24 hrs. four leaves out of the +seventeen were well inflected, together with the blades of two; six were +slightly affected, and seven not at all. Three leaves of one lot were observed +for five days, and all died; but in another lot of six, all excepting one +looked healthy after four days. Three leaves were immersed during 9 hrs., each +in 30 minims of a solution of one part to 875 of water, and were not in the +least affected; but they ought to have been observed for a longer time. +</p> + +<p> +Potassium, Chloride of. Neither half-minims of a solution of one part to 437 of +water; left on the discs of six leaves for three days, nor the immersion of +three leaves during 25 hrs., in 30 minims of a solution of one part to 875 of +water, produced the least effect. The immersed leaves were then treated with +carbonate of ammonia, as described under nitrate of potash, and with the same +result. +</p> + +<p> +Potassium, Iodide of.—Half-minims of a solution of one part to 437 of +water were placed on the discs of seven leaves. In 30 m. one leaf had the blade +inflected; after some hours three leaves had most of their submarginal +tentacles moderately inflected; the remaining three being very slightly +affected. Hardly any of these leaves had their outer tentacles inflected. After +21 hrs. all re-expanded, excepting two which still had a few submarginal +tentacles inflected. Three leaves were next [page 181] immersed for 8 hrs. 40 +m., each in 30 minims of a solution of one part to 875 of water, and were not +in the least affected. I do not know what to conclude from this conflicting +evidence; but it is clear that the iodide of potassium does not generally +produce any marked effect. +</p> + +<p> +Potassium, Bromide of.—Half-minims of a solution of one part to 437 of +water were placed on the discs of six leaves; after 22 hrs. one had its blade +and many tentacles inflected, but I suspect that an insect might have alighted +on it and then escaped; the five other leaves were in no way affected. I tested +three of these leaves with bits of meat, and after 24 hrs. they became +splendidly inflected. Three leaves were also immersed for 21 hrs. in 30 minims +of a solution of one part to 875 of water; but they were not at all affected, +excepting that the glands looked rather pale. +</p> + +<p> +Lithium, Acetate of.—Four leaves were immersed together in a vessel +containing 120 minims of a solution of one part to 437 of water; so that each +received, if the leaves absorbed equally, 1/16 of a grain. After 24 hrs. there +was no inflection. I then added, for the sake of testing the leaves, some +strong solution (viz. 1 gr. to 20 oz., or one part to 8750 of water) of +phosphate of ammonia, and all four became in 30 m. closely inflected. +</p> + +<p> +Lithium, Nitrate of.—Four leaves were immersed, as in the last case, in +120 minims of a solution of one part to 437 of water; after 1 h. 30 m. all four +were a little, and after 24 hrs. greatly, inflected. I then diluted the +solution with some water, but they still remained somewhat inflected on the +third day. +</p> + +<p> +Caesium, Chloride of.—Four leaves were immersed, as above, in 120 minims +of a solution of one part to 437 of water. After 1 hr. 5 m. the glands were +darkened; after 4 hrs. 20 m. there was a trace of inflection; after 6 hrs. 40 +m. two leaves were greatly, but not closely, and the other two considerably +inflected. After 22 hrs. the inflection was extremely great, and two had their +blades inflected. I then transferred the leaves into water, and in 46 hrs. from +their first immersion they were almost re-expanded. +</p> + +<p> +Rubidium, Chloride of.—Four leaves which were immersed, as above, in 120 +minims of a solution of one part to 437 of water, were not acted on in 22 hrs. +I then added some of the strong solution (1 gr. to 20 oz.) of phosphate of +ammonia, and in 30 m. all were immensely inflected. +</p> + +<p> +Silver, Nitrate of.—Three leaves were immersed in ninety [page 182] +minims of a solution of one part to 437 of water; so that each received, as +before, 1/16 of a grain. After 5 m. slight inflection, and after 11 m. very +strong inflection, the glands becoming excessively black; after 40 m. all the +tentacles were closely inflected. After 6 hrs. the leaves were taken out of the +solution, washed, and placed in water; but next morning they were evidently +dead. +</p> + +<p> +Calcium, Acetate of.—Four leaves were immersed in 120 minims of a +solution of one part to 437 of water; after 24 hrs. none of the tentacles were +inflected, excepting a few where the blade joined the petiole; and this may +have been caused by the absorption of the salt by the cut-off end of the +petiole. I then added some of the solution (1 gr. to 20 oz.) of phosphate of +ammonia, but this to my surprise excited only slight inflection, even after 24 +hrs. Hence it would appear that the acetate had rendered the leaves torpid. +</p> + +<p> +Calcium, Nitrate of.—Four leaves were immersed in 120 minims of a +solution of one part to 437 of water, but were not affected in 24 hrs. I then +added some of the solution of phosphate of ammonia (1 gr. to 20 oz.), but this +caused only very slight inflection after 24 hrs. A fresh leaf was next put into +a mixed solution of the above strengths of the nitrate of calcium and phosphate +of ammonia, and it became closely inflected in between 5 m. and 10 m. +Half-minims of a solution of one part of the nitrate of calcium to 218 of water +were dropped on the discs of three leaves, but produced no effect. +</p> + +<p> +Magnesium, Acetate, Nitrate, and Chloride of.—Four leaves were immersed +in 120 minims of solutions, of one part to 437 of water, of each of these three +salts; after 6 hrs. there was no inflection; but after 22 hrs. one of the +leaves in the acetate was rather more inflected than generally occurs from an +immersion for this length of time in water. Some of the solution (1 gr. to 20 +oz.) of phosphate of ammonia was then added to the three solutions. The leaves +in the acetate mixed with the phosphate underwent some inflection; and this was +well pronounced after 24 hrs. Those in the mixed nitrate were decidedly +inflected in 4 hrs. 30 m., but the degree of inflection did not afterwards much +increase; whereas the four leaves in the mixed chloride were greatly inflected +in a few minutes, and after 4 hrs. had almost every tentacle closely inflected. +We thus see that the acetate and nitrate of magnesium injure the leaves, or at +least prevent the subsequent action of phosphate of ammonia; whereas the +chloride has no such tendency. [page 183] +</p> + +<p> +Magnesium, Sulphate of.—Half-minims of a solution of one part to 218 of +water were placed on the discs of ten leaves, and produced no effect. +</p> + +<p> +Barium, Acetate of.—Four leaves were immersed in 120 minims of a solution +of one part to 437 of water, and after 22 hrs. there was no inflection, but the +glands were blackened. The leaves were then placed in a solution (1 gr. to 20 +oz.) of phosphate of ammonia, which caused after 26 hrs. only a little +inflection in two of the leaves. +</p> + +<p> +Barium, Nitrate of.—Four leaves were immersed in 120 minims of a solution +of one part to 437 of water; and after 22 hrs. there was no more than that +slight degree of inflection, which often follows from an immersion of this +length in pure water. I then added some of the same solution of phosphate of +ammonia, and after 30 m. one leaf was greatly inflected, two others moderately, +and the fourth not at all. The leaves remained in this state for 24 hrs. +</p> + +<p> +Strontium, Acetate of.—Four leaves, immersed in 120 minims of a solution +of one part to 437 of water, were not affected in 22 hrs. They were then placed +in some of the same solution of phosphate of ammonia, and in 25 m. two of them +were greatly inflected; after 8 hrs. the third leaf was considerably inflected, +and the fourth exhibited a trace of inflection. They were in the same state +next morning. +</p> + +<p> +Strontium, Nitrate of.—Five leaves were immersed in 120 minims of a +solution of one part to 437 of water; after 22 hrs. there was some slight +inflection, but not more than sometimes occurs with leaves in water. They were +then placed in the same solution of phosphate of ammonia; after 8 hrs. three of +them were moderately inflected, as were all five after 24 hrs.; but not one was +closely inflected. It appears that the nitrate of strontium renders the leaves +half torpid. +</p> + +<p> +Cadmium, Chloride of.—Three leaves were immersed in ninety minims of a +solution of one part to 437 of water; after 5 hrs. 20 m. slight inflection +occurred, which increased during the next three hours. After 24 hrs. all three +leaves had their tentacles well inflected, and remained so for an additional 24 +hrs.; glands not discoloured. +</p> + +<p> +Mercury, Perchloride of.—Three leaves were immersed in ninety minims of a +solution of one part to 437 of water; after 22 m. there was some slight +inflection, which in 48 m. became well pronounced; the glands were now +blackened. After 5 hrs. 35 m. all the tentacles closely inflected; after 24 +hrs. still [page 184] inflected and discoloured. The leaves were then removed +and left for two days in water; but they never re-expanded, being evidently +dead. +</p> + +<p> +Zinc, Chloride of.—Three leaves immersed in ninety minims of a solution +of one part to 437 of water were not affected in 25 hrs. 30 m. +</p> + +<p> +Aluminium, Chloride of.—Four leaves were immersed in 120 minims of a +solution of one part to 437 of water; after 7 hrs. 45 m. no inflection; after +24 hrs. one leaf rather closely, the second moderately, the third and fourth +hardly at all, inflected. The evidence is doubtful, but I think some power in +slowly causing inflection must be attributed to this salt. These leaves were +then placed in the solution (1 gr. to 20 oz.) of phosphate of ammonia, and +after 7 hrs. 30 m. the three, which had been but little affected by the +chloride, became rather closely inflected. +</p> + +<p> +Aluminium, Nitrate of.—Four leaves were immersed in 120 minims of a +solution of one part to 437 of water; after 7 hrs. 45 m. there was only a trace +of inflection; after 24 hrs. one leaf was moderately inflected. The evidence is +here again doubtful, as in the case of the chloride of aluminium. The leaves +were then transferred to the same solution, as before, of phosphate of ammonia; +this produced hardly any effect in 7 hrs. 30 m.; but after 25 hrs. one leaf was +pretty closely inflected, the three others very slightly, perhaps not more so +than from water. +</p> + +<p> +Aluminium and Potassium, Sulphate of (common alum).—Half-minims of a +solution of the usual strength were placed on the discs of nine leaves, but +produced no effect. +</p> + +<p> +Gold, Chloride of.—Seven leaves were immersed in so much of a solution of +one part to 437 of water that each received 30 minims, containing 1/16 of a +grain, or 4.048 mg., of the chloride. There was some inflection in 8 m., which +became extreme in 45 m. In 3 hrs. the surrounding fluid was coloured purple, +and the glands were blackened. After 6 hrs. the leaves were transferred to +water; next morning they were found discoloured and evidently killed. The +secretion decomposes the chloride very readily; the glands themselves becoming +coated with the thinnest layer of metallic gold, and particles float about on +the surface of the surrounding fluid. +</p> + +<p> +Lead, Chloride of.—Three leaves were immersed in ninety minims of a +solution of one part to 437 of water. After 23 hrs. there was not a trace of +inflection; the glands were not blackened, and the leaves did not appear +injured. They were then trans- [page 185] ferred to the solution (1 gr. to 20 +oz.) of phosphate of ammonia, and after 24 hrs. two of them were somewhat, the +third very little, inflected; and they thus remained for another 24 hrs. +</p> + +<p> +Tin, Chloride of.—Four leaves were immersed in 120 minims of a solution +of about one part (all not being dissolved) to 437 of water. After 4 hrs. no +effect; after 6 hrs. 30 m. all four leaves had their submarginal tentacles +inflected; after 22 hrs. every single tentacle and the blades were closely +inflected. The surrounding fluid was now coloured pink. The leaves were washed +and transferred to water, but next morning were evidently dead. This chloride +is a deadly poison, but acts slowly. +</p> + +<p> +Antimony, Tartrate of.—Three leaves were immersed in ninety minims of a +solution of one part to 437 of water. After 8 hrs. 30 m. there was slight +inflection; after 24 hrs. two of the leaves were closely, and the third +moderately, inflected; glands not much darkened. The leaves were washed and +placed in water, but they remained in the same state for 48 additional hours. +This salt is probably poisonous, but acts slowly. +</p> + +<p> +Arsenious Acid.—A solution of one part to 437 of water; three leaves were +immersed in ninety minims; in 25 m. considerable inflection; in 1 h. great +inflection; glands not discoloured. After 6 hrs. the leaves were transferred to +water; next morning they looked fresh, but after four days were pale-coloured, +had not re-expanded, and were evidently dead. +</p> + +<p> +Iron, Chloride of.—Three leaves were immersed in ninety minims of a +solution of one part to 437 of water; in 8 hrs. no inflection; but after 24 +hrs. considerable inflection; glands blackened; fluid coloured yellow, with +floating flocculent particles of oxide of iron. The leaves were then placed in +water; after 48 hrs. they had re-expanded a very little, but I think were +killed; glands excessively black. +</p> + +<p> +Chromic Acid.—One part to 437 of water; three leaves were immersed in +ninety minims; in 30 m. some, and in 1 hr. considerable, inflection; after 2 +hrs. all the tentacles closely inflected, with the glands discoloured. Placed +in water, next day leaves quite discoloured and evidently killed. +</p> + +<p> +Manganese, Chloride of.—Three leaves immersed in ninety minims of a +solution of one part to 437 of water; after 22 hrs. no more inflection than +often occurs in water; glands not blackened. The leaves were then placed in the +usual solution of phosphate of ammonia, but no inflection was caused even after +48 hrs. +</p> + +<p> +Copper, Chloride of.—Three leaves immersed in ninety minims [page 186] of +a solution of one part to 437 of water; after 2 hrs. some inflection; after 3 +hrs. 45 m. tentacles closely inflected, with the glands blackened. After 22 +hrs. still closely inflected, and the leaves flaccid. Placed in pure water, +next day evidently dead. A rapid poison. +</p> + +<p> +Nickel, Chloride of.—Three leaves immersed in ninety minims of a solution +of one part to 437 of water; in 25 m. considerable inflection, and in 3 hrs. +all the tentacles closely inflected. After 22 hrs. still closely inflected; +most of the glands, but not all, blackened. The leaves were then placed in +water; after 24 hrs. remained inflected; were somewhat discoloured, with the +glands and tentacles dingy red. Probably killed. +</p> + +<p> +Cobalt, Chloride of.—Three leaves immersed in ninety minims of a solution +of one part to 437 of water; after 23 hrs. there was not a trace of inflection, +and the glands were not more blackened than often occurs after an equally long +immersion in water. +</p> + +<p> +Platinum, Chloride of.—Three leaves immersed in ninety minims of a +solution of one part to 437 of water; in 6 m. some inflection, which became +immense after 48 m. After 3 hrs. the glands were rather pale. After 24 hrs. all +the tentacles still closely inflected; glands colourless; remained in same +state for four days; leaves evidently killed.] +</p> + +<p> +Concluding Remarks on the Action of the foregoing Salts.—Of the fifty-one +salts and metallic acids which were tried, twenty-five caused the tentacles to +be inflected, and twenty-six had no such effect, two rather doubtful cases +occurring in each series. In the table at the head of this discussion, the +salts are arranged according to their chemical affinities; but their action on +Drosera does not seem to be thus governed. The nature of the base is far more +important, as far as can be judged from the few experiments here given, than +that of the acid; and this is the conclusion at which physiologists have +arrived with respect to animals. We see this fact illustrated in all the nine +salts of soda causing inflection, and in not being poisonous except when given +in large doses; whereas seven of [page 187] the corresponding salts of potash +do not cause inflection, and some of them are poisonous. Two of them, however, +viz. the oxalate and iodide of potash, slowly induced a slight and rather +doubtful amount of inflection. This difference between the two series is +interesting, as Dr. Burdon Sanderson informs me that sodium salts may be +introduced in large doses into the circulation of mammals without any injurious +effects; whilst small doses of potassium salts cause death by suddenly +arresting the movements of the heart. An excellent instance of the different +action of the two series is presented by the phosphate of soda quickly causing +vigorous inflection, whilst phosphate of potash is quite inefficient. The great +power of the former is probably due to the presence of phosphorus, as in the +cases of phosphate of lime and of ammonia. Hence we may infer that Drosera +cannot obtain phosphorus from the phosphate of potash. This is remarkable, as I +hear from Dr. Burdon Sanderson that phosphate of potash is certainly decomposed +within the bodies of animals. Most of the salts of soda act very rapidly; the +iodide acting slowest. The oxalate, nitrate, and citrate seem to have a special +tendency to cause the blade of the leaf to be inflected. The glands of the +disc, after absorbing the citrate, transmit hardly any motor impulse to the +outer tentacles; and in this character the citrate of soda resembles the +citrate of ammonia, or a decoction of grass-leaves; these three fluids all +acting chiefly on the blade. +</p> + +<p> +It seems opposed to the rule of the preponderant influence of the base that the +nitrate of lithium causes moderately rapid inflection, whereas the acetate +causes none; but this metal is closely allied to sodium [page 188] and +potassium,* which act so differently; therefore we might expect that its action +would be intermediate. We see, also, that caesium causes inflection, and +rubidium does not; and these two metals are allied to sodium and potassium. +Most of the earthy salts are inoperative. Two salts of calcium, four of +magnesium, two of barium, and two of strontium, did not cause any inflection, +and thus follow the rule of the preponderant power of the base. Of three salts +of aluminium, one did not act, a second showed a trace of action, and the third +acted slowly and doubtfully, so that their effects are nearly alike. +</p> + +<p> +Of the salts and acids of ordinary metals, seventeen were tried, and only four, +namely those of zinc, lead, manganese, and cobalt, failed to cause inflection. +The salts of cadmium, tin, antimony, and iron, act slowly; and the three latter +seem more or less poisonous. The salts of silver, mercury, gold, copper, +nickel, and platinum, chromic and arsenious acids, cause great inflection with +extreme quickness, and are deadly poisons. It is surprising, judging from +animals, that lead and barium should not be poisonous. Most of the poisonous +salts make the glands black, but chloride of platinum made them very pale. I +shall have occasion, in the next chapter, to add a few remarks on the different +effects of phosphate of ammonia on leaves previously immersed in various +solutions. +</p> + +<p class="center"> +A<small>CIDS</small>. +</p> + +<p> +I will first give, as in the case of the salts, a list of the twenty-four acids +which were tried, divided into two series, according as they cause or do not +cause +</p> + +<p class="footnote"> +* Miller’s ‘Elements of Chemistry,’ 3rd edit. pp. 337, 448. +[page 189] +</p> + +<p> +inflection. After describing the experiments, a few concluding remarks will be +added. +</p> + +<p class="center"> +ACIDS, MUCH DILUTED, WHICH CAUSE INFLECTION. +</p> + +<p> +1. Nitric, strong inflection; poisonous. 2. Hydrochloric, moderate and slow +inflection; not poisonous. 3. Hydriodic, strong inflection; poisonous. 4. +Iodic, strong inflection; poisonous. 5. Sulphuric, strong inflection; somewhat +poisonous. 6. Phosphoric, strong inflection; poisonous. 7. Boracic; moderate +and rather slow inflection; not poisonous. 8. Formic, very slight inflection; +not poisonous. 9. Acetic, strong and rapid inflection; poisonous. 10. +Propionic, strong but not very rapid inflection; poisonous. 11. Oleic, quick +inflection; very poisonous. 12. Carbolic, very slow inflection; poisonous. 13. +Lactic, slow and moderate inflection; poisonous. 14. Oxalic, moderately quick +inflection; very poisonous. 15. Malic, very slow but considerable inflection; +not poisonous. 16. Benzoic, rapid inflection; very poisonous. 17. Succinic, +moderately quick inflection: moderately poisonous. 18. Hippuric, rather slow +inflection; poisonous. 19. Hydrocyanic, rather rapid inflection; very +poisonous. +</p> + +<p class="center"> +ACIDS, DILUTED TO THE SAME DEGREE, WHICH DO NOT CAUSE INFLECTION. +</p> + +<p> +1. Gallic; not poisonous. 2. Tannic; not poisonous. 3. Tartaric; not poisonous. +4. Citric; not poisonous. 5. Uric; (?) not poisonous. +</p> + +<p> +Nitric Acid.—Four leaves were placed, each in thirty minims of one part +by weight of the acid to 437 of water, so that each received 1/16 of a grain, +or 4.048 mg. This strength was chosen for this and most of the following +experiments, as it is the same [page 190] as that of most of the foregoing +saline solutions. In 2 hrs. 30 m. some of the leaves were considerably, and in +6 hrs. 30 m. all were immensely, inflected, as were their blades. The +surrounding fluid was slightly coloured pink, which always shows that the +leaves have been injured. They were then left in water for three days; but they +remained inflected and were evidently killed. Most of the glands had become +colourless. Two leaves were then immersed, each in thirty minims of one part to +1000 of water; in a few hours there was some inflection; and after 24 hrs. both +leaves had almost all their tentacles and blades inflected; they were left in +water for three days, and one partially re-expanded and recovered. Two leaves +were next immersed, each in thirty minims of one part to 2000 of water; this +produced very little effect, except that most of the tentacles close to the +summit of the petiole were inflected, as if the acid had been absorbed by the +cut-off end. +</p> + +<p> +Hydrochloric Acid.—One part to 437 of water; four leaves were immersed as +before, each in thirty minims. After 6 hrs. only one leaf was considerably +inflected. After 8 hrs. 15 m. one had its tentacles and blade well inflected; +the other three were moderately inflected, and the blade of one slightly. The +surrounding fluid was not coloured at all pink. After 25 hrs. three of these +four leaves began to re-expand, but their glands were of a pink instead of a +red colour; after two more days they fully re-expanded; but the fourth leaf +remained inflected, and seemed much injured or killed, with its glands white. +Four leaves were then treated, each with thirty minims of one part to 875 of +water; after 21 hrs. they were moderately inflected; and on being transferred +to water, fully re-expanded in two days, and seemed quite healthy. +</p> + +<p> +Hydriodic Acid.—One to 437 of water; three leaves were immersed as +before, each in thirty minims. After 45 m. the glands were discoloured, and the +surrounding fluid became pinkish, but there was no inflection. After 5 hrs. all +the tentacles were closely inflected; and an immense amount of mucus was +secreted, so that the fluid could be drawn out into long ropes. The leaves were +then placed in water, but never re-expanded, and were evidently killed. Four +leaves were next immersed in one part to 875 of water; the action was now +slower, but after 22 hrs. all four leaves were closely inflected, and were +affected in other respects as above described. These leaves did not re-expand, +though left for four days in water. This acid acts far more powerfully than +hydrochloric, and is poisonous. +</p> + +<p> +Iodic Acid.—One to 437 of water; three leaves were immersed, [page 191] +each in thirty minims; after 3 hrs. strong inflection; after 4 hrs. glands dark +brown; after 8 hrs. 30 m. close inflection, and the leaves had become flaccid; +surrounding fluid not coloured pink. These leaves were then placed in water, +and next day were evidently dead. +</p> + +<p> +Sulphuric Acid.—One to 437 of water; four leaves were immersed, each in +thirty minims; after 4 hrs. great inflection; after 6 hrs. surrounding fluid +just tinged pink; they were then placed in water, and after 46 hrs. two of them +were still closely inflected, two beginning to re-expand; many of the glands +colourless. This acid is not so poisonous as hydriodic or iodic acids. +</p> + +<p> +Phosphoric Acid.—One to 437 of water; three leaves were immersed together +in ninety minims; after 5 hrs. 30 m. some inflection, and some glands +colourless; after 8 hrs. all the tentacles closely inflected, and many glands +colourless; surrounding fluid pink. Left in water for two days and a half, +remained in the same state and appeared dead. +</p> + +<p> +Boracic Acid.—One to 437 of water; four leaves were immersed together in +120 minims; after 6 hrs. very slight inflection; after 8 hrs. 15 m. two were +considerably inflected, the other two slightly. After 24 hrs. one leaf was +rather closely inflected, the second less closely, the third and fourth +moderately. The leaves were washed and put into water; after 24 hrs. they were +almost fully re-expanded and looked healthy. This acid agrees closely with +hydrochloric acid of the same strength in its power of causing inflection, and +in not being poisonous. +</p> + +<p> +Formic Acid.—Four leaves were immersed together in 120 minims of one part +to 437 of water; after 40 m. slight, and after 6 hrs. 30 m. very moderate +inflection; after 22 hrs. only a little more inflection than often occurs in +water. Two of the leaves were then washed and placed in a solution (1 gr. to 20 +oz.) of phosphate of ammonia; after 24 hrs. they were considerably inflected, +with the contents of their cells aggregated, showing that the phosphate had +acted, though not to the full and ordinary degree. +</p> + +<p> +Acetic Acid.—Four leaves were immersed together in 120 minims of one part +to 437 of water. In 1 hr. 20 m. the tentacles of all four and the blades of two +were greatly inflected. After 8 hrs. the leaves had become flaccid, but still +remained closely inflected, the surrounding fluid being coloured pink. They +were then washed and placed in water; next morning they were still inflected +and of a very dark red colour, but with their glands colourless. After another +day they were dingy-coloured, and [page 192] evidently dead. This acid is far +more powerful than formic, and is highly poisonous. Half-minim drops of a +stronger mixture (viz. one part by measure to 320 of water) were placed on the +discs of five leaves; none of the exterior tentacles, only those on the borders +of the disc which actually absorbed the acid, became inflected. Probably the +dose was too strong and paralysed the leaves, for drops of a weaker mixture +caused much inflection; nevertheless the leaves all died after two days. +</p> + +<p> +Propionic Acid.—Three leaves were immersed in ninety minims of a mixture +of one part to 437 of water; in 1 hr. 50 m. there was no inflection; but after +3 hrs. 40 m. one leaf was greatly inflected, and the other two slightly. The +inflection continued to increase, so that in 8 hrs. all three leaves were +closely inflected. Next morning, after 20 hrs., most of the glands were very +pale, but some few were almost black. No mucus had been secreted, and the +surrounding fluid was only just perceptibly tinted of a pale pink. After 46 +hrs. the leaves became slightly flaccid and were evidently killed, as was +afterwards proved to be the case by keeping them in water. The protoplasm in +the closely inflected tentacles was not in the least aggregated, but towards +their bases it was collected in little brownish masses at the bottoms of the +cells. This protoplasm was dead, for on leaving the leaf in a solution of +carbonate of ammonia, no aggregation ensued. Propionic acid is highly poisonous +to Drosera, like its ally acetic acid, but induces inflection at a much slower +rate. +</p> + +<p> +Oleic Acid (given me by Prof. Frankland).—Three leaves were immersed in +this acid; some inflection was almost immediately caused, which increased +slightly, but then ceased, and the leaves seemed killed. Next morning they were +rather shrivelled, and many of the glands had fallen off the tentacles. Drops +of this acid were placed on the discs of four leaves; in 40 m. all the +tentacles were greatly inflected, excepting the extreme marginal ones; and many +of these after 3 hrs. became inflected. I was led to try this acid from +supposing that it was present (which does not seem to be the case)* in olive +oil, the action of which is anomalous. Thus drops of this oil placed on the +disc do not cause the outer tentacles to be inflected; yet when minute drops +were added to the secretion surrounding the glands of the outer tentacles, +these were occasionally, but by no means always, inflected. Two leaves were +also immersed in this oil, and there +</p> + +<p class="footnote"> +* See articles on Glycerine and Oleic Acid in Watts’ ‘Dict. of +Chemistry.’ [page 193] +</p> + +<p> +was no inflection for about 12 hrs.; but after 23 hrs. almost all the tentacles +were inflected. Three leaves were likewise immersed in unboiled linseed oil, +and soon became somewhat, and in 3 hrs. greatly, inflected. After 1 hr. the +secretion round the glands was coloured pink. I infer from this latter fact +that the power of linseed oil to cause inflection cannot be attributed to the +albumin which it is said to contain. +</p> + +<p> +Carbolic Acid.—Two leaves were immersed in sixty minims of a solution of +1 gr. to 437 of water; in 7 hrs. one was slightly, and in 24 hrs. both were +closely, inflected, with a surprising amount of mucus secreted. These leaves +were washed and left for two days in water; they remained inflected; most of +their glands became pale, and they seemed dead. This acid is poisonous, but +does not act nearly so rapidly or powerfully as might have been expected from +its known destructive power on the lowest organisms. Half-minims of the same +solution were placed on the discs of three leaves; after 24 hrs. no inflection +of the outer tentacles ensued, and when bits of meat were given them, they +became fairly well inflected. Again half-minims of a stronger solution, of one +part to 218 of water, were placed on the discs of three leaves; no inflection +of the outer tentacles ensued; bits of meat were then given as before; one leaf +alone became well inflected, the discal glands of the other two appearing much +injured and dry. We thus see that the glands of the discs, after absorbing this +acid, rarely transmit any motor impulse to the outer tentacles; though these, +when their own glands absorb the acid, are strongly acted on. +</p> + +<p> +Lactic Acid.—Three leaves were immersed in ninety minims of one part to +437 of water. After 48 m. there was no inflection, but the surrounding fluid +was coloured pink; after 8 hrs. 30 m. one leaf alone was a little inflected, +and almost all the glands on all three leaves were of a very pale colour. The +leaves were then washed and placed in a solution (1 gr. to 20 oz.) of phosphate +of ammonia; after about 16 hrs. there was only a trace of inflection. They were +left in the phosphate for 48 hrs., and remained in the same state, with almost +all their glands discoloured. The protoplasm within the cells was not +aggregated, except in a very few tentacles, the glands of which were not much +discoloured. I believe, therefore, that almost all the glands and tentacles had +been killed by the acid so suddenly that hardly any inflection was caused. Four +leaves were next immersed in 120 minims of a weaker solution, of one part to +875 of water; after 2 hrs. 30 m. the surrounding fluid was quite pink; the +glands were pale, but [page 194] there was no inflection; after 7 hrs. 30 m. +two of the leaves showed some inflection, and the glands were almost white; +after 21 hrs. two of the leaves were considerably inflected, and a third +slightly; most of the glands were white, the others dark red. After 45 hrs. one +leaf had almost every tentacle inflected; a second a large number; the third +and fourth very few; almost all the glands were white, excepting those on the +discs of two of the leaves, and many of these were very dark red. The leaves +appeared dead. Hence lactic acid acts in a very peculiar manner, causing +inflection at an extraordinarily slow rate, and being highly poisonous. +Immersion in even weaker solutions, viz. of one part to 1312 and 1750 of water, +apparently killed the leaves (the tentacles after a time being bowed +backwards), and rendered the glands white, but caused no inflection. +</p> + +<p> +Gallic, Tannic, Tartaric, and Citric Acids.—One part to 437 of water. +Three or four leaves were immersed, each in thirty minims of these four +solutions, so that each leaf received 1/16 of a grain, or 4.048 mg. No +inflection was caused in 24 hrs., and the leaves did not appear at all injured. +Those which had been in the tannic and tartaric acids were placed in a solution +(1 gr. to 20 oz.) of phosphate of ammonia, but no inflection ensued in 24 hrs. +On the other hand, the four leaves which had been in the citric acid, when +treated with the phosphate, became decidedly inflected in 50 m. and strongly +inflected after 5 hrs., and so remained for the next 24 hrs. +</p> + +<p> +Malic Acid.—Three leaves were immersed in ninety minims of a solution of +one part to 437 of water; no inflection was caused in 8 hrs. 20 m., but after +24 hrs. two of them were considerably, and the third slightly, +inflected—more so than could be accounted for by the action of water. No +great amount of mucus was secreted. They were then placed in water, and after +two days partially re-expanded. Hence this acid is not poisonous. +</p> + +<p> +Oxalic Acid.—Three leaves were immersed in ninety minims of a solution of +1 gr. to 437 of water; after 2 hrs. 10 m. there was much inflection; glands +pale; the surrounding fluid of a dark pink colour; after 8 hrs. excessive +inflection. The leaves were then placed in water; after about 16 hrs. the +tentacles were of a very dark red colour, like those of the leaves in acetic +acid. After 24 additional hours, the three leaves were dead and their glands +colourless. +</p> + +<p> +Benzoic Acid.—Five leaves were immersed, each in thirty minims of a +solution of 1 gr. to 437 of water. This solution was so weak that it only just +tasted acid, yet, as we shall see, was highly poisonous to Drosera. After 52 m. +the submarginal [page 195] tentacles were somewhat inflected, and all the +glands very pale-coloured; the surrounding fluid was coloured pink. On one +occasion the fluid became pink in the course of only 12 m., and the glands as +white as if the leaf had been dipped in boiling water. After 4 hrs. much +inflection; but none of the tentacles were closely inflected, owing, as I +believe, to their having been paralysed before they had time to complete their +movement. An extraordinary quantity of mucus was secreted. Some of the leaves +were left in the solution; others, after an immersion of 6 hrs. 30 m., were +placed in water. Next morning both lots were quite dead; the leaves in the +solution being flaccid, those in the water (now coloured yellow) of a pale +brown tint, and their glands white. +</p> + +<p> +Succinic Acid.—Three leaves were immersed in ninety minims of a solution +of 1 gr. to 437 of water; after 4 hrs. 15 m. considerable and after 23 hrs. +great inflection; many of the glands pale; fluid coloured pink. The leaves were +then washed and placed in water; after two days there was some re-expansion, +but many of the glands were still white. This acid is not nearly so poisonous +as oxalic or benzoic. +</p> + +<p> +Uric Acid.—Three leaves were immersed in 180 minims of a solution of 1 +gr. to 875 of warm water, but all the acid was not dissolved; so that each +received nearly 1/16 of a grain. After 25 m. there was some slight inflection, +but this never increased; after 9 hrs. the glands were not discoloured, nor was +the solution coloured pink; nevertheless much mucus was secreted. The leaves +were then placed in water, and by next morning fully re-expanded. I doubt +whether this acid really causes inflection, for the slight movement which at +first occurred may have been due to the presence of a trace of albuminous +matter. But it produces some effect, as shown by the secretion of so much +mucus. +</p> + +<p> +Hippuric Acid.—Four leaves were immersed in 120 minims of a solution of 1 +gr. to 437 of water. After 2 hrs. the fluid was coloured pink; glands pale, but +no inflection. After 6 hrs. some inflection; after 9 hrs. all four leaves +greatly inflected; much mucus secreted; all the glands very pale. The leaves +were then left in water for two days; they remained closely inflected, with +their glands colourless, and I do not doubt were killed. +</p> + +<p> +Hydrocyanic Acid.—Four leaves were immersed, each in thirty minims of one +part to 437 of water; in 2 hrs. 45 m. all the tentacles were considerably +inflected, with many of the glands pale; after 3 hrs. 45 m. all strongly +inflected, and the surrounding fluid coloured pink; after 6 hrs. all closely +inflected. After [page 196] an immersion of 8 hrs. 20 m. the leaves were washed +and placed in water; next morning, after about 16 hrs., they were still +inflected and discoloured; on the succeeding day they were evidently dead. Two +leaves were immersed in a stronger mixture, of one part to fifty of water; in 1 +hr. 15 m. the glands became as white as porcelain, as if they had been dipped +in boiling water; very few of the tentacles were inflected; but after 4 hrs. +almost all were inflected. These leaves were then placed in water, and next +morning were evidently dead. Half-minim drops of the same strength (viz. one +part to fifty of water) were next placed on the discs of five leaves; after 21 +hrs. all the outer tentacles were inflected, and the leaves appeared much +injured. I likewise touched the secretion round a large number of glands with +minute drops (about 1/20 of a minim, or .00296 ml.) of Scheele’s mixture +(6 per cent.); the glands first became bright red, and after 3 hrs. 15 m. about +two-thirds of the tentacles bearing these glands were inflected, and remained +so for the two succeeding days, when they appeared dead.] +</p> + +<p> +Concluding Remarks on the Action of Acids.—It is evident that acids have +a strong tendency to cause the inflection of the tentacles;* for out of the +twenty-four acids tried, nineteen thus acted, either rapidly and energetically, +or slowly and slightly. This fact is remarkable, as the juices of many plants +contain more acid, judging by the taste, than the solutions employed in my +experiments. From the powerful effects of so many acids on Drosera, we are led +to infer that those naturally contained in the tissues of this plant, as well +as of others, must play some important part in their economy. Of the five cases +in which acids did not cause the tentacles to be inflected, one is doubtful; +for uric acid did act slightly, and caused a copious secretion of mucus. Mere +sourness to the taste is no +</p> + +<p class="footnote"> +* According to M. Fournier (‘De la Fcondation dans les +Phanrogames.’ 1863, p. 61) drops of acetic, hydrocyanic, and sulphuric +acid cause the stamens of Berberis instantly to close; though drops of water +have no such power, which latter statement I can confirm; [page 197] +</p> + +<p> +criterion of the power of an acid on Drosera, as citric and tartaric acids are +very sour, yet do not excite inflection. It is remarkable how acids differ in +their power. Thus, hydrochloric acid acts far less powerfully than hydriodic +and many other acids of the same strength, and is not poisonous. This is an +interesting fact, as hydrochloric acid plays so important a part in the +digestive process of animals. Formic acid induces very slight inflection, and +is not poisonous; whereas its ally, acetic acid, acts rapidly and powerfully, +and is poisonous. Malic acid acts slightly, whereas citric and tartaric acids +produce no effect. Lactic acid is poisonous, and is remarkable from inducing +inflection only after a considerable interval of time. Nothing surprised me +more than that a solution of benzoic acid, so weak as to be hardly acidulous to +the taste, should act with great rapidity and be highly poisonous; for I am +informed that it produces no marked effect on the animal economy. It may be +seen, by looking down the list at the head of this discussion, that most of the +acids are poisonous, often highly so. Diluted acids are known to induce +negative osmose,* and the poisonous action of so many acids on Drosera is, +perhaps, connected with this power, for we have seen that the fluids in which +they were immersed often became pink, and the glands pale-coloured or white. +Many of the poisonous acids, such as hydriodic, benzoic, hippuric, and carbolic +(but I neglected to record all the cases), caused the secretion of an +extraordinary amount of mucus, so that long ropes of this matter hung from the +leaves when they were lifted out of the solutions. Other acids, such as +hydrochloric and malic, have no such ten- +</p> + +<p class="footnote"> +* Miller’s ‘Elements of Chemistry,’ part i. 1867, p. 87. +[page 198] +</p> + +<p> +dency; in these two latter cases the surrounding fluid was not coloured pink, +and the leaves were not poisoned. On the other hand, propionic acid, which is +poisonous, does not cause much mucus to be secreted, yet the surrounding fluid +became slightly pink. Lastly, as in the case of saline solutions, leaves, after +being immersed in certain acids, were soon acted on by phosphate of ammonia; on +the other hand, they were not thus affected after immersion in certain other +acids. To this subject, however, I shall have to recur. [page 199] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0009" id="link2HCH0009"></a> +CHAPTER IX.<br/> +THE EFFECTS OF CERTAIN ALKALOID POISONS, OTHER SUBSTANCES AND VAPOURS.</h2> + +<p class="letter"> +Strychnine, salts of—Quinine, sulphate of, does not soon arrest the +movement of the protoplasm—Other salts of +quinine—Digitaline—Nicotine—Atropine—Veratrine— +Colchicine— +Theine—Curare—Morphia—Hyoscyamus—Poison of the cobra, +apparently accelerates the movements of the protoplasm—Camphor, a +powerful stimulant, its vapour narcotic—Certain essential oils excite +movement—Glycerine—Water and certain solutions retard or prevent +the subsequent action of phosphate of ammonia—Alcohol innocuous, its +vapour narcotic and poisonous—Chloroform, sulphuric and nitric ether, +their stimulant, poisonous, and narcotic power—Carbonic acid narcotic, +not quickly poisonous—Concluding remarks. +</p> + +<p> +As in the last chapter, I will first give my experiments, and then a brief +summary of the results with some concluding remarks. +</p> + +<p> +[Acetate of Strychnine.—Half-minims of a solution of one part to 437 of +water were placed on the discs of six leaves; so that each received 1/960 of a +grain, or .0675 mg. In 2 hrs. 30 m. the outer tentacles on some of them were +inflected, but in an irregular manner, sometimes only on one side of the leaf. +The next morning, after 22 hrs. 30 m. the inflection had not increased. The +glands on the central disc were blackened, and had ceased secreting. After an +additional 24 hrs. all the central glands seemed dead, but the inflected +tentacles had re-expanded and appeared quite healthy. Hence the poisonous +action of strychnine seems confined to the glands which have absorbed it; +nevertheless, these glands transmit a motor impulse to the exterior tentacles. +Minute drops (about 1/20 of a minim) of the same solution applied to the glands +of the outer tentacles occasionally caused them to bend. The poison does not +seem to act quickly, for having applied to several glands similar drops of a +rather stronger solution, of one part to 292 of water, this did not prevent the +tentacles bending, when their glands [page 200] were excited, after an interval +of a quarter to three quarters of an hour, by being rubbed or given bits of +meat. Similar drops of a solution of one part to 218 of water (2 grs. to 1 oz.) +quickly blackened the glands; some few tentacles thus treated moved, whilst +others did not. The latter, however, on being subsequently moistened with +saliva or given bits of meat, became incurved, though with extreme slowness; +and this shows that they had been injured. Stronger solutions (but the strength +was not ascertained) sometimes arrested all power of movement very quickly; +thus bits of meat were placed on the glands of several exterior tentacles, and +as soon as they began to move, minute drops of the strong solution were added. +They continued for a short time to go on bending, and then suddenly stood +still; other tentacles on the same leaves, with meat on their glands, but not +wetted with the strychnine, continued to bend and soon reached the centre of +the leaf. +</p> + +<p> +Citrate of Strychnine.—Half-minims of a solution of one part to 437 of +water were placed on the discs of six leaves; after 24 hrs. the outer tentacles +showed only a trace of inflection. Bits of meat were then placed on three of +these leaves, but in 24 hrs. only slight and irregular inflection occurred, +proving that the leaves had been greatly injured. Two of the leaves to which +meat had not been given had their discal glands dry and much injured. Minute +drops of a strong solution of one part to 109 of water (4 grs. to 1 oz.) were +added to the secretion round several glands, but did not produce nearly so +plain an effect as the drops of a much weaker solution of the acetate. +Particles of the dry citrate were placed on six glands; two of these moved some +way towards the centre, and then stood still, being no doubt killed; three +others curved much farther inwards, and were then fixed; one alone reached the +centre. Five leaves were immersed, each in thirty minims of a solution of one +part to 437 of water; so that each received 1/16 of a grain; after about 1 hr. +some of the outer tentacles became inflected, and the glands were oddly mottled +with black and white. These glands, in from 4 hrs. to 5 hrs., became whitish +and opaque, and the protoplasm in the cells of the tentacles was well +aggregated. By this time two of the leaves were greatly inflected, but the +three others not much more inflected than they were before. Nevertheless two +fresh leaves, after an immersion respectively for 2 hrs. and 4 hrs. in the +solution, were not killed; for on being left for 1 hr. 30 m. in a solution of +one part of carbonate of ammonia to 218 of water, their tentacles became more +inflected, and there was much aggregation. The glands [page 201] of two other +leaves, after an immersion for 2 hrs. in a stronger solution, of one part of +the citrate to 218 of water, became of an opaque, pale pink colour, which +before long disappeared, leaving them white. One of these two leaves had its +blade and tentacles greatly inflected; the other hardly at all; but the +protoplasm in the cells of both was aggregated down to the bases of the +tentacles, with the spherical masses in the cells close beneath the glands +blackened. After 24 hrs. one of these leaves was colourless, and evidently +dead. +</p> + +<p> +Sulphate of Quinine.—Some of this salt was added to water, which is said +to dissolve 1/1000 part of its weight. Five leaves were immersed, each in +thirty minims of this solution, which tasted bitter. In less than 1 hr. some of +them had a few tentacles inflected. In 3 hrs. most of the glands became +whitish, others dark-coloured, and many oddly mottled. After 6 hrs. two of the +leaves had a good many tentacles inflected, but this very moderate degree of +inflection never increased. One of the leaves was taken out of the solution +after 4 hrs., and placed in water; by the next morning some few of the +inflected tentacles had re-expanded, showing that they were not dead; but the +glands were still much discoloured. Another leaf not included in the above lot, +after an immersion of 3 hrs. 15 m., was carefully examined; the protoplasm in +the cells of the outer tentacles, and of the short green ones on the disc, had +become strongly aggregated down to their bases; and I distinctly saw that the +little masses changed their positions and shapes rather rapidly; some +coalescing and again separating. I was surprised at this fact, because quinine +is said to arrest all movement in the white corpuscles of the blood; but as, +according to Binz,* this is due to their being no longer supplied with oxygen +by the red corpuscles, any such arrestment of movement could not be expected in +Drosera. That the glands had absorbed some of the salt was evident from their +change of colour; but I at first thought that the solution might not have +travelled down the cells of the tentacles, where the protoplasm was seen in +active movement. This view, however, I have no doubt, is erroneous, for a leaf +which had been immersed for 3 hrs. in the quinine solution was then placed in a +little solution of one part of carbonate of ammonia to 218 of water; and in 30 +m. the glands and the upper cells of the tentacles became intensely black, with +the protoplasm presenting a very unusual appearance; for it +</p> + +<p class="footnote"> +* ‘Quarterly Journal of Microscopical Science,’ April 1874, p. 185. +[page 202] +</p> + +<p> +had become aggregated into reticulated dingy-coloured masses, having rounded +and angular interspaces. As I have never seen this effect produced by the +carbonate of ammonia alone, it must be attributed to the previous action of the +quinine. These reticulated masses were watched for some time, but did not +change their forms; so that the protoplasm no doubt had been killed by the +combined action of the two salts, though exposed to them for only a short time. +</p> + +<p> +Another leaf, after an immersion for 24 hrs. in the quinine solution, became +somewhat flaccid, and the protoplasm in all the cells was aggregated. Many of +the aggregated masses were discoloured, and presented a granular appearance; +they were spherical, or elongated, or still more commonly consisted of little +curved chains of small globules. None of these masses exhibited the least +movement, and no doubt were all dead. +</p> + +<p> +Half-minims of the solution were placed on the discs of six leaves; after 23 +hrs. one had all its tentacles, two had a few, and the others none inflected; +so that the discal glands, when irritated by this salt, do not transmit any +strong motor impulse to the outer tentacles. After 48 hrs. the glands on the +discs of all six leaves were evidently much injured or quite killed. It is +clear that this salt is highly poisonous.* +</p> + +<p> +Acetate of Quinine.—Four leaves were immersed, each in thirty minims of a +solution of one part to 437 of water. The solution was tested with litmus +paper, and was not acid. After only 10 m. all four leaves were greatly, and +after 6 hrs. immensely, inflected. They were then left in water for 60 hrs., +but never re-expanded; the glands were white, and the leaves evidently dead. +This salt is far more efficient than the sulphate in causing inflection, and, +like that salt, is highly poisonous. +</p> + +<p> +Nitrate of Quinine.—Four leaves were immersed, each in thirty minims of a +solution of one part to 437 of water. After 6 hrs. there was hardly a trace of +inflection; after 22 hrs. three of the leaves were moderately, and the fourth +slightly inflected; so that this salt induces, though rather slowly, +well-marked inflection. These leaves, on being left in water for 48 hrs., +almost +</p> + +<p class="footnote"> +*Binz found several years ago (as stated in ‘The Journal of Anatomy and +Phys.’ November 1872, p. 195) that quinia is an energetic poison to low +vegetable and animal organisms. Even one part added to 4000 parts of blood +arrests the movements of the white corpuscles, which become “rounded and +granular.” In the tentacles of Drosera the aggregated masses of +protoplasm, which appeared killed by the quinine, likewise presented a granular +appearance. A similar appearance is caused by very hot water. [page 203] +</p> + +<p> +completely re-expanded, but the glands were much discoloured. Hence this salt +is not poisonous in any high degree. The different action of the three +foregoing salts of quinine is singular. +</p> + +<p> +Digitaline.—Half-minims of a solution of one part to 437 of water were +placed on the discs of five leaves. In 3 hrs. 45 m. Some of them had their +tentacles, and one had its blade, moderately inflected. After 8 hrs. three of +them were well inflected; the fourth had only a few tentacles inflected, and +the fifth (an old leaf) was not at all affected. They remained in nearly the +same state for two days, but the glands on their discs became pale. On the +third day the leaves appeared much injured. Nevertheless, when bits of meat +were placed on two of them, the outer tentacles became inflected. A minute drop +(about 1/20 of a minim) of the solution was applied to three glands, and after +6 hrs. all three tentacles were inflected, but next day had nearly re-expanded; +so that this very small dose of 1/28800 of a grain (.00225 mg.) acts on a +tentacle, but is not poisonous. It appears from these several facts that +digitaline causes inflection, and poisons the glands which absorb a moderately +large amount. +</p> + +<p> +Nicotine.—The secretion round several glands was touched with a minute +drop of the pure fluid, and the glands were instantly blackened; the tentacles +becoming inflected in a few minutes. Two leaves were immersed in a weak +solution of two drops to 1 oz., or 437 grains, of water. When examined after 3 +hrs. 20 m., only twenty-one tentacles on one leaf were closely inflected, and +six on the other slightly so; but all the glands were blackened, or very +dark-coloured, with the protoplasm in all the cells of all the tentacles much +aggregated and dark-coloured. The leaves were not quite killed, for on being +placed in a little solution of carbonate of ammonia (2 grs. to 1 oz.) a few +more tentacles became inflected, the remainder not being acted on during the +next 24 hrs. +</p> + +<p> +Half-minims of a stronger solution (two drops to 1/2 oz. of water) were placed +on the discs of six leaves, and in 30 m. all those tentacles became inflected; +the glands of which had actually touched the solution, as shown by their +blackness; but hardly any motor influence was transmitted to the outer +tentacles. After 22 hrs. most of the glands on the discs appeared dead; but +this could not have been the case, as when bits of meat were placed on three of +them, some few of the outer tentacles were inflected in 24 hrs. Hence nicotine +has a great tendency to blacken the glands and to induce aggregation [page 204] +of the protoplasm, but, except when pure, has very moderate power of inducing +inflection, and still less power of causing a motor influence to be transmitted +from the discal glands to the outer tentacles. It is moderately poisonous. +</p> + +<p> +Atropine.—A grain was added to 437 grains of water, but was not all +dissolved; another grain was added to 437 grains of a mixture of one part of +alcohol to seven parts of water; and a third solution was made by adding one +part of valerianate of atropine to 437 of water. Half-minims of these three +solutions were placed, in each case, on the discs of six leaves; but no effect +whatever was produced, excepting that the glands on the discs to which the +valerianate was given were slightly discoloured. The six leaves on which drops +of the solution of atropine in diluted alcohol had been left for 21 hrs. were +given bits of meat, and all became in 24 hrs. fairly well inflected; so that +atropine does not excite movement, and is not poisonous. I also tried in the +same manner the alkaloid sold as daturine, which is believed not to differ from +atropine, and it produced no effect. Three of the leaves on which drops of this +latter solution had been left for 24 hrs. were likewise given bits of meat, and +they had in the course of 24 hrs. a good many of their submarginal tentacles +inflected. +</p> + +<p> +Veratrine, Colchicine, Theine.—Solutions were made of these three +alkaloids by adding one part to 437 of water. Half-minims were placed, in each +case; on the discs of at least six leaves, but no inflection was caused, except +perhaps a very slight amount by the theine. Half-minims of a strong infusion of +tea likewise produced, as formerly stated, no effect. I also tried similar +drops of an infusion of one part of the extract of colchicum, sold by +druggists, to 218 of water; and the leaves were observed for 48 hrs., without +any effect being produced. The seven leaves on which drops of veratrine had +been left for 26 hrs. were given bits of meat, and after 21 hrs. were well +inflected. These three alkaloids are therefore quite innocuous. +</p> + +<p> +Curare.—One part of this famous poison was added to 218 of water, and +three leaves were immersed in ninety minims of the filtered solution. In 3 hrs. +30 m. some of the tentacles were a little inflected; as was the blade of one; +after 4 hrs. After 7 hrs. the glands were wonderfully blackened, showing that +matter of some kind had been absorbed. In 9 hrs. two of the leaves had most of +their tentacles sub-inflected, but the inflection did not increase in the +course of 24 hrs. One of these leaves, after being immersed for 9 hrs. in the +solution, was placed in water, and by next morning had largely re-expanded; +[page 205] the other two, after their immersion for 24 hrs., were likewise +placed in water, and in 24 hrs. were considerably re-expanded, though their +glands were as black as ever. Half-minims were placed on the discs of six +leaves, and no inflection ensued; but after three days the glands on the discs +appeared rather dry, yet to my surprise were not blackened. On another occasion +drops were placed on the discs of six leaves, and a considerable amount of +inflection was soon caused; but as I had not filtered the solution, floating +particles may have acted on the glands. After 24 hrs. bits of meat were placed +on the discs of three of these leaves, and next day they became strongly +inflected. As I at first thought that the poison might not have been dissolved +in pure water, one grain was added to 437 grains of a mixture of one part of +alcohol to seven of water, and half-minims were placed on the discs of six +leaves. These were not at all affected, and when after a day bits of meat were +given them, they were slightly inflected in 5 hrs., and closely after 24 hrs. +It follows from these several facts that a solution of curare induces a very +moderate degree of inflection, and this may perhaps be due to the presence of a +minute quantity of albumen. It certainly is not poisonous. The protoplasm in +one of the leaves, which had been immersed for 24 hrs., and which had become +slightly inflected, had undergone a very slight amount of aggregation—not +more than often ensues from an immersion of this length of time in water. +</p> + +<p> +Acetate of Morphia.—I tried a great number of experiments with this +substance, but with no certain result. A considerable number of leaves were +immersed from between 2 hrs. and 6 hrs. in a solution of one part to 218 of +water, and did not become inflected. Nor were they poisoned; for when they were +washed and placed in weak solutions of phosphate and carbonate of ammonia, they +soon became strongly inflected, with the protoplasm in the cells well +aggregated. If, however, whilst the leaves were immersed in the morphia, +phosphate of ammonia was added, inflection did not rapidly ensue. Minute drops +of the solution were applied in the usual manner to the secretion round between +thirty and forty glands; and when, after an interval of 6 m:, bits of meat, a +little saliva, or particles of glass, were placed on them, the movement of the +tentacles was greatly retarded. But on other occasions no such retardation +occurred. Drops of water similarly applied never have any retarding power. +Minute drops of a solution of sugar of the same strength (one part to 218 of +water) sometimes retarded the subsequent action of meat and of particles of +glass, and [page 206] sometimes did not do so. At one time I felt convinced +that morphia acted as a narcotic on Drosera, but after having found in what a +singular manner immersion in certain non-poisonous salts and acids prevents the +subsequent action of phosphate of ammonia, whereas other solutions have no such +power, my first conviction seems very doubtful. +</p> + +<p> +Extract of Hyoscyamus.—Several leaves were placed, each in thirty minims +of an infusion of 3 grs. of the extract sold by druggists to 1 oz. of water. +One of them, after being immersed for 5 hrs. 15 m., was not inflected, and was +then put into a solution (1 gr. to 1 oz.) of carbonate of ammonia; after 2 hrs. +40 m. it was found considerably inflected, and the glands much blackened. Four +of the leaves, after being immersed for 2 hrs. 14 m., were placed in 120 minims +of a solution (1 gr. to 20 oz.) of phosphate of ammonia; they had already +become slightly inflected from the hyoscyamus, probably owing to the presence +of some albuminous matter, as formerly explained, but the inflection +immediately increased, and after 1 hr. was strongly pronounced; so that +hyoscyamus does not act as a narcotic or poison. +</p> + +<p> +Poison from the Fang of a Living Adder.—Minute drops were placed on the +glands of many tentacles; these were quickly inflected, just as if saliva had +been given them, Next morning, after 17 hrs. 30 m., all were beginning to +re-expand, and they appeared uninjured. +</p> + +<p> +Poison from the Cobra.—Dr. Fayrer, well known from his investigations on +the poison of this deadly snake, was so kind as to give me some in a dried +state. It is an albuminous substance, and is believed to replace the ptyaline +of saliva.* A minute drop (about 1/20 of a minim) of a solution of one part to +437 of water was applied to the secretion round four glands; so that each +received only about 1/38400 of a grain (.0016 mg.). The operation was repeated +on four other glands; and in 15 m. several of the eight tentacles became well +inflected, and all of them in 2 hrs. Next morning, after 24 hrs., they were +still inflected, and the glands of a very pale pink colour. After an additional +24 hrs. they were nearly re-expanded, and completely so on the succeeding day; +but most of the glands remained almost white. +</p> + +<p> +Half-minims of the same solution were placed on the discs of three leaves, so +that each received 1/960 of a grain (.0675 mg.); in +</p> + +<p class="footnote"> +*Dr. Fayrer, ‘The Thanatophidia of India,’ 1872, p. 150. [page 207] +</p> + +<p> +4 hrs. 15 m. the outer tentacles were much inflected; and after 6 hrs. 30 m. +those on two of the leaves were closely inflected and the blade of one; the +third leaf was only moderately affected. The leaves remained in the same state +during the next day, but after 48 hrs. re-expanded. +</p> + +<p> +Three leaves were now immersed, each in thirty minims of the solution, so that +each received 1/16 of a grain, or 4.048 mg. In 6 m. there was some inflection, +which steadily increased, so that after 2 hrs. 30 m. all three leaves were +closely inflected; the glands were at first somewhat darkened, then rendered +pale; and the protoplasm within the cells of the tentacles was partially +aggregated. The little masses of protoplasm were examined after 3 hrs., and +again after 7 hrs., and on no other occasion have I seen them undergoing such +rapid changes of form. After 8 hrs. 30 m. the glands had become quite white; +they had not secreted any great quantity of mucus. The leaves were now placed +in water, and after 40 hrs. re-expanded, showing that they were not much or at +all injured. During their immersion in water the protoplasm within the cells of +the tentacles was occasionally examined, and always found in strong movement. +</p> + +<p> +Two leaves were next immersed, each in thirty minims of a much stronger +solution, of one part to 109 of water; so that each received 1/4 of a grain, or +16.2 mg; After 1 hr. 45 m. the sub-marginal tentacles were strongly inflected, +with the glands somewhat pale; after 3 hrs. 30 m. both leaves had all their +tentacles closely inflected and the glands white. Hence the weaker solution, as +in so many other cases, induced more rapid inflection than the stronger one; +but the glands were sooner rendered white by the latter. After an immersion of +24 hrs. some of the tentacles were examined, and the protoplasm, still of a +fine purple colour, was found aggregated into chains of small globular masses. +These changed their shapes with remarkable quickness. After an immersion of 48 +hrs. they were again examined, and their movements were so plain that they +could easily be seen under a weak power. The leaves were now placed in water, +and after 24 hrs. (i.e. 72 hrs. from their first immersion) the little masses +of protoplasm, which had become of a dingy purple, were still in strong +movement, changing their shapes, coalescing, and again separating. +</p> + +<p> +In 8 hrs. after these two leaves had been placed in water (i.e. in 56 hrs. +after their immersion in the solution) they began to re-expand, and by the next +morning were more expanded. After an additional day (i.e. on the fourth day +after their immersion in the solution) they were largely, but not quite fully +[page 208] expanded. The tentacles were now examined, and the aggregated masses +were almost wholly redissolved; the cells being filled with homogeneous purple +fluid, with the exception here and there of a single globular mass. We thus see +how completely the protoplasm had escaped all injury from the poison. As the +glands were soon rendered quite white, it occurred to me that their texture +might have been modified in such a manner as to prevent the poison passing into +the cells beneath, and consequently that the protoplasm within these cells had +not been at all affected. Accordingly I placed another leaf, which had been +immersed for 48 hrs. in the poison and afterwards for 24 hrs. in water, in a +little solution of one part of carbonate of ammonia to 218 of water; in 30 m. +the protoplasm in the cells beneath the glands became darker, and in the course +of 24 hrs. the tentacles were filled down to their bases with dark-coloured +spherical masses. Hence the glands had not lost their power of absorption, as +far as the carbonate of ammonia is concerned. +</p> + +<p> +From these facts it is manifest that the poison of the cobra, though so deadly +to animals, is not at all poisonous to Drosera; yet it causes strong and rapid +inflection of the tentacles, and soon discharges all colour from the glands. It +seems even to act as a stimulant to the protoplasm, for after considerable +experience in observing the movements of this substance in Drosera, I have +never seen it on any other occasion in so active a state. I was therefore +anxious to learn how this poison affected animal protoplasm; and Dr. Fayrer was +so kind as to make some observations for me, which he has since published.* +Ciliated epithelium from the mouth of a frog was placed in a solution of .03 +gramme to 4.6 cubic cm. of water; others being placed at the same time in pure +water for comparison. The movements of the cilia in the solution seemed at +first increased, but soon languished, and after between 15 and 20 minutes +ceased; whilst those in the water were still acting vigorously. The white +corpuscles of the blood of a frog, and the cilia on two infusorial animals, a +Paramaecium and Volvox, were similarly affected by the poison. Dr. Fayrer also +found that the muscle of a frog lost its irritability after an immersion of 20 +m. in the solution, not then responding to a strong electrical current. On the +other hand, the movements of the cilia on the mantle of an Unio were not always +arrested, even when left for a consider- +</p> + +<p class="footnote"> +* ‘Proceedings of Royal Society,’ Feb. 18, 1875. [page 209] +</p> + +<p> +able time in a very strong solution. On the whole, it seems that the poison of +the cobra acts far more injuriously on the protoplasm of the higher animals +than on that of Drosera. +</p> + +<p> +There is one other point which may be noticed. I have occasionally observed +that the drops of secretion round the glands were rendered somewhat turbid by +certain solutions, and more especially by some acids, a film being formed on +the surfaces of the drops; but I never saw this effect produced in so +conspicuous a manner as by the cobra poison. When the stronger solution was +employed, the drops appeared in 10 m. like little white rounded clouds. After +48 hrs. the secretion was changed into threads and sheets of a membranous +substance, including minute granules of various sizes. +</p> + +<p> +Camphor.—Some scraped camphor was left for a day in a bottle with +distilled water, and then filtered. A solution thus made is said to contain +1/1000 of its weight of camphor; it smelt and tasted of this substance. Ten +leaves were immersed in this solution; after 15 m. five of them were well +inflected, two showing a first trace of movement in 11 m. and 12 m.; the sixth +leaf did not begin to move until 15 m. had elapsed, but was fairly well +inflected in 17 m. and quite closed in 24 m.; the seventh began to move in 17 +m., and was completely shut in 26 m. The eighth, ninth, and tenth leaves were +old and of a very dark red colour, and these were not inflected after an +immersion of 24 hrs.; so that in making experiments with camphor it is +necessary to avoid such leaves. Some of these leaves, on being left in the +solution for 4 hrs., became of a rather dingy pink colour, and secreted much +mucus; although their tentacles were closely inflected, the protoplasm within +the cells was not at all aggregated. On another occasion, however, after a +longer immersion of 24 hrs., there was well marked aggregation. A solution made +by adding two drops of camphorated spirits to an ounce of water did not act on +one leaf; whereas thirty minims added to an ounce of water acted on two leaves +immersed together. +</p> + +<p> +M. Vogel has shown* that the flowers of various plants do not wither so soon +when their stems are placed in a solution of camphor as when in water; and that +if already slightly withered, they recover more quickly. The germination of +certain seeds is also accelerated by the solution. So that camphor acts as a +stimulant, and it is the only known stimulant for plants. I +</p> + +<p class="footnote"> +* ‘Gardener’s Chronicle,’ 1874, p. 671. Nearly similar +observations were made in 1798 by B. S. Barton. [page 210] +</p> + +<p> +wished, therefore, to ascertain whether camphor would render the leaves of +Drosera more sensitive to mechanical irritation than they naturally are. Six +leaves were left in distilled water for 5 m. or 6 m., and then gently brushed +twice or thrice, whilst still under water, with a soft camel-hair brush; but no +movement ensued. Nine leaves, which had been immersed in the above solution of +camphor for the times stated in the following table, were next brushed only +once with the same brush and in the same manner as before; the results are +given in the table. My first trials were made by brushing the leaves whilst +still immersed in the solution; but it occurred to me that the viscid secretion +round the glands would thus be removed, and the camphor might act more +effectually on them. In all the following trials, therefore, each leaf was +taken out of the solution, waved for about 15 s. in water, then placed in fresh +water and brushed, so that the brushing would not allow the freer access of the +camphor; but this treatment made no difference in the results. +</p> + +<p> +Column 1 : Number of Leaves. Column 2 : Length of Immersion in the Solution of +Camphor. Column 3 : Length of Time between the Act of Brushing and the +Inflection of the Tentacles. Column 4 : Length of Time between the Immersion of +the Leaves in the Solution and the First Sign of the Inflection of the +Tentacles. +</p> + +<p> +1 : 5 m. : 3 m. considerable inflection; 4 m. all the tentacles except 3 or 4 +inflected. : 8 m. +</p> + +<p> +2 : 5 m. : 6 m. first sign of inflection. : 11 m. +</p> + +<p> +3 : 5 m. : 6 m. 30 s. slight inflection; 7 m. 30 s. plain inflection. : 11 m. +30 s. +</p> + +<p> +4 : 4 m. 30 s. : 2 m. 30 s. a trace of inflection; 3 m. plain; 4 m. strongly +marked. : 7 m. +</p> + +<p> +5 : 4 m. : 2 m. 30 s. a trace of inflection; 3 m. plain inflection. : 6 m. 30 +s. +</p> + +<p> +6 : 4 m. : 2 m. 30 s. decided inflection; 3 m. 30 s. strongly marked. : 6 m. 30 +s. +</p> + +<p> +7 : 4 m. : 2 m. 30 s. slight inflection; 3 m. plain; 4 m. well marked. : 6 m. +30 s. +</p> + +<p> +8 : 3 m. : 2 m. trace of inflection; 3 m. considerable, 6 m. strong inflection. +: 5 m. +</p> + +<p> +9 : 3 m. : 2 m. trace of inflection; 3 m. considerable, 6 m. strong inflection. +: 5 m. +</p> + +<p> +Other leaves were left in the solution without being brushed; one of these +first showed a trace of inflection after 11 m.; a second after 12 m.; five were +not inflected until 15 m. had [page 211] elapsed, and two not until a few +minutes later. On the other hand, it will be seen in the right-hand column of +the table that most of the leaves subjected to the solution, and which were +brushed, became inflected in a much shorter time. The movement of the tentacles +of some of these leaves was so rapid that it could be plainly seen through a +very weak lens. +</p> + +<p> +Two or three other experiments are worth giving. A large old leaf, after being +immersed for 10 m. in the solution, did not appear likely to be soon inflected; +so I brushed it, and in 2 m. it began to move, and in 3 m. was completely shut. +Another leaf, after an immersion of 15 m., showed no signs of inflection, so +was brushed, and in 4 m. was grandly inflected. A third leaf, after an +immersion of 17 m., likewise showed no signs of inflection; it was then +brushed, but did not move for 1 hr.; so that here was a failure. It was again +brushed, and now in 9 m. a few tentacles became inflected; the failure +therefore was not complete. +</p> + +<p> +We may conclude that a small dose of camphor in solution is a powerful +stimulant to Drosera. It not only soon excites the tentacles to bend, but +apparently renders the glands sensitive to a touch, which by itself does not +cause any movement. Or it may be that a slight mechanical irritation not enough +to cause any inflection yet gives some tendency to movement, and thus +reinforces the action of the camphor. This latter view would have appeared to +me the more probable one, had it not been shown by M. Vogel that camphor is a +stimulant in other ways to various plants and seeds. +</p> + +<p> +Two plants bearing four or five leaves, and with their roots in a little cup of +water, were exposed to the vapour of some bits of camphor (about as large as a +filbert-nut), under a vessel holding ten fluid oz. After 10 hrs. no inflection +ensued; but the glands appeared to be secreting more copiously. The leaves were +in a narcotised condition, for on bits of meat being placed on two of them, +there was no inflection in 3 hrs. 15 m., and even after 13 hrs. 15 m. only a +few of the outer tentacles were slightly inflected; but this degree of movement +shows that the leaves had not been killed by an exposure during 10 hrs. to the +vapour of camphor. +</p> + +<p> +Oil of Caraway.—Water is said to dissolve about a thousandth part of its +weight of this oil. A drop was added to an ounce of water and the bottle +occasionally shaken during a day; but many minute globules remained +undissolved. Five leaves were immersed in this mixture; in from 4 m. to 5 m. +there was some inflection, which became moderately pronounced in two or [page +212] three additional minutes. After 14 m. all five leaves were well, and some +of them closely, inflected. After 6 hrs. the glands were white, and much mucus +had been secreted. The leaves were now flaccid, of a peculiar dull-red colour, +and evidently dead. One of the leaves, after an immersion of 4 m., was brushed, +like the leaves in the camphor, but this produced no effect. A plant with its +roots in water was exposed under a 10-oz. vessel to the vapour of this oil, and +in 1 hr. 20 m. one leaf showed a trace of inflection. After 5 hrs. 20 m. the +cover was taken off and the leaves examined; one had all its tentacles closely +inflected, the second about half in the same state; and the third all +sub-inflected. The plant was left in the open air for 42 hrs., but not a single +tentacle expanded; all the glands appeared dead, except here and there one, +which was still secreting. It is evident that this oil is highly exciting and +poisonous to Drosera. +</p> + +<p> +Oil of Cloves.—A mixture was made in the same manner as in the last case, +and three leaves were immersed in it. After 30 m. there was only a trace of +inflection which never increased. After 1 hr. 30 m. the glands were pale, and +after 6 hrs. white. No doubt the leaves were much injured or killed. +</p> + +<p> +Turpentine.—Small drops placed on the discs of some leaves killed them, +as did likewise drops of creosote. A plant was left for 15 m. under a 12-oz. +vessel, with its inner surface wetted with twelve drops of turpentine; but no +movement of the tentacles ensued. After 24 hrs. the plant was dead. +</p> + +<p> +Glycerine.—Half-minims were placed on the discs of three leaves: in 2 +hrs. some of the outer tentacles were irregularly inflected; and in 19 hrs. the +leaves were flaccid and apparently dead; the glands which had touched the +glycerine were colourless. Minute drops (about 1/20 of a minim) were applied to +the glands of several tentacles, and in a few minutes these moved and soon +reached the centre. Similar drops of a mixture of four dropped drops to 1 oz. +of water were likewise applied to several glands; but only a few of the +tentacles moved, and these very slowly and slightly. Half-minims of this same +mixture placed on the discs of some leaves caused, to my surprise, no +inflection in the course of 48 hrs. Bits of meat were then given them, and next +day they were well inflected; notwithstanding that some of the discal glands +had been rendered almost colourless. Two leaves were immersed in the same +mixture, but only for 4 hrs.; they were not inflected, and on being afterwards +left for 2 hrs. 30 m. in a solution (1 gr. to 1 oz.) of carbonate of ammonia, +their glands were blackened, their tentacles inflected, and the protoplasm +within their cells aggregated. It appears [page 213] from these facts that a +mixture of four drops of glycerine to an ounce of water is not poisonous, and +excites very little inflection; but that pure glycerine is poisonous, and if +applied in very minute quantities to the glands of the outer tentacles causes +their inflection. +</p> + +<p> +The Effects of Immersion in Water and in various Solutions on the subsequent +Action of Phosphate and Carbonate of Ammonia.—We have seen in the third +and seventh chapters that immersion in distilled water causes after a time some +degree of aggregation of the protoplasm, and a moderate amount of inflection, +especially in the case of plants which have been kept at a rather high +temperature. Water does not excite a copious secretion of mucus. We have here +to consider the effects of immersion in various fluids on the subsequent action +of salts of ammonia and other stimulants. Four leaves which had been left for +24 hrs. in water were given bits of meat, but did not clasp them. Ten leaves, +after a similar immersion, were left for 24 hrs. in a powerful solution (1 gr. +to 20 oz.) of phosphate of ammonia, and only one showed even a trace of +inflection. Three of these leaves, on being left for an additional day in the +solution, still remained quite unaffected. When, however, some of these leaves, +which had been first immersed in water for 24 hrs., and then in the phosphate +for 24 hrs. were placed in a solution of carbonate of ammonia (one part to 218 +of water), the protoplasm in the cells of the tentacles became in a few hours +strongly aggregated, showing that this salt had been absorbed and taken effect. +</p> + +<p> +A short immersion in water for 20 m. did not retard the subsequent action of +the phosphate, or of splinters of glass placed on the glands; but in two +instances an immersion for 50 m. prevented any effect from a solution of +camphor. Several leaves which had been left for 20 m. in a solution of one part +of white sugar to 218 of water were placed in the phosphate solution, the +action of which was delayed; whereas a mixed solution of sugar and the +phosphate did not in the least interfere with the effects of the latter. Three +leaves, after being immersed for 20 m. in the sugar solution, were placed in a +solution of carbonate of ammonia (one part to 218 of water); in 2 m. or 3 m. +the glands were blackened, and after 7 m. the tentacles were considerably +inflected, so that the solution of sugar, though it delayed the action of the +phosphate, did not delay that of the carbonate. Immersion in a similar solution +of gum arabic for 20 m. had no retarding action on the phosphate. Three leaves +were left for 20 m. in a mixture of one part of alcohol to seven parts of +water, [page 214] and then placed in the phosphate solution: in 2 hrs. 15 m. +there was a trace of inflection in one leaf, and in 5 hrs. 30 m. a second was +slightly affected; the inflection subsequently increased, though slowly. Hence +diluted alcohol, which, as we shall see, is hardly at all poisonous, plainly +retards the subsequent action of the phosphate. +</p> + +<p> +It was shown in the last chapter that leaves which did not become inflected by +nearly a day’s immersion in solutions of various salts and acids behaved +very differently from one another when subsequently placed in the phosphate +solution. I here give a table summing up the results. +</p> + +<p> +Column 1 : Name of the Salts and Acids in Solution. Column 2 : Period of +Immersion of the Leaves in Solutions of one part to 437 of water. Column 3 : +Effects produced on the Leaves by their subsequent Immersion for stated periods +in a Solution of one part of phosphate of ammonia to 8750 of water, or 1 gr. to +20 oz. +</p> + +<p> +Rubidium chloride. : 22 hrs. : After 30 m. strong inflection of the tentacles. +</p> + +<p> +Potassium carbonate : 20 m. : Scarcely any inflection until 5 hrs. had elapsed. +</p> + +<p> +Calcium acetate. : 24 hrs. : After 24 hrs. very slight inflection. +</p> + +<p> +Calcium nitrate. : 24 hrs. : Do. do. +</p> + +<p> +Magnesium acetate. : 22 hrs. : Some slight inflection, which became well +pronounced in 24 hrs. +</p> + +<p> +Magnesium nitrate. : 22 hrs. : After 4 hrs. 30 m. a fair amount of inflection, +which never increased. +</p> + +<p> +Magnesium chloride : 22 hrs. : After a few minutes great inflection; after 4 +hrs. all four leaves with almost every tentacle closely inflected. +</p> + +<p> +Barium acetate. : 22 hrs. : After 24 hrs. two leaves out of four slightly +inflected. +</p> + +<p> +Barium nitrate. : 22 hrs. : After 30 m. one leaf greatly, and two others +moderately, inflected; they remained thus for 24 hrs. +</p> + +<p> +Strontium acetate. : 22 hrs. : After 25 m. two leaves greatly inflected; after +8 hrs. a third leaf moderately, and the fourth very slightly, inflected. All +four thus remained for 24 hrs. +</p> + +<p> +Strontium nitrate. : 22 hrs. : After 8 hrs. three leaves out of five moderately +inflected; after 24 hrs. all five in this state; but not one closely inflected. +</p> + +<p> +Aluminium chloride : 24 hrs. : Three leaves which had either been slightly or +not at all affected by the chloride became after 7 hrs. 30 m. rather closely +inflected. [page 215] +</p> + +<p> +Column 1 : Name of the Salts and Acids in Solution. Column 2 : Period of +Immersion of the Leaves in Solutions of one part to 437 of water. Column 3 : +Effects produced on the Leaves by their subsequent Immersion for stated periods +in a Solution of one part of phosphate of ammonia to 8750 of water, or 1 gr. to +20 oz. +</p> + +<p> +Aluminium nitrate. : 24 hrs. : After 25 hrs. slight and doubtful effect. +</p> + +<p> +Lead chloride. : 23 hrs. : After 24 hrs. two leaves somewhat inflected, the +third very little; and thus remained. +</p> + +<p> +Manganese chloride : 22 hrs. : After 48 hrs. not the least inflection. +</p> + +<p> +Lactic acid. : 48 hrs. : After 24 hrs. a trace of inflection in a few +tentacles, the glands of which had not been killed by the acid. +</p> + +<p> +Tannic acid. : 24 hrs. : After 24 hrs. no inflection. +</p> + +<p> +Tartaric acid. : 24 hrs. : Do. do. +</p> + +<p> +Citric acid. : 24 hrs. : After 50 m. tentacles decidedly inflected, and after 5 +hrs. strongly inflected; so remained for the next 24 hrs. +</p> + +<p> +Formic acid. : 22 hrs. : Not observed until 24 hrs. had elapsed; tentacles +considerably inflected, and protoplasm aggregated. +</p> + +<p> +In a large majority of these twenty cases, a varying degree of inflection was +slowly caused by the phosphate. In four cases, however, the inflection was +rapid, occurring in less than half an hour or at most in 50 m. In three cases +the phosphate did not produce the least effect. Now what are we to infer from +these facts? We know from ten trials that immersion in distilled water for 24 +hrs. prevents the subsequent action of the phosphate solution. It would, +therefore, appear as if the solutions of chloride of manganese, tannic and +tartaric acids, which are not poisonous, acted exactly like water, for the +phosphate produced no effect on the leaves which had been previously immersed +in these three solutions. The majority of the other solutions behaved to a +certain extent like water, for the phosphate produced, after a considerable +interval of time, only a slight effect. On the other hand, the leaves which had +been immersed in the solutions of the chloride of rubidium and magnesium, of +acetate of strontium, nitrate of barium, and citric acid, were quickly acted on +by the phosphate. Now was water absorbed from these five weak solutions, and +yet, owing to the presence of the salts, did not prevent the subsequent action +of the phosphate? Or [page 216] may we not suppose* that the interstices of the +walls of the glands were blocked up with the molecules of these five +substances, so that they were rendered impermeable to water; for had water +entered, we know from the ten trials that the phosphate would not afterwards +have produced any effect? It further appears that the molecules of the +carbonate of ammonia can quickly pass into glands which, from having been +immersed for 20 m. in a weak solution of sugar, either absorb the phosphate +very slowly or are acted on by it very slowly. On the other hand, glands, +however they may have been treated, seem easily to permit the subsequent +entrance of the molecules of carbonate of ammonia. Thus leaves which had been +immersed in a solution (of one part to 437 of water) of nitrate of potassium +for 48 hrs.—of sulphate of potassium for 24 hrs.—and of the +chloride of potassium for 25 hrs.—on being placed in a solution of one +part of carbonate of ammonia to 218 of water, had their glands immediately +blackened, and after 1 hr. their tentacles somewhat inflected, and the +protoplasm aggregated. But it would be an endless task to endeavour to +ascertain the wonderfully diversified effects of various solutions on Drosera. +</p> + +<p> +Alcohol (one part to seven of water).—It has already been shown that +half-minims of this strength placed on the discs of leaves do not cause any +inflection; and that when two days afterwards the leaves were given bits of +meat, they became strongly inflected. Four leaves were immersed in this +mixture, and two of them after 30 m. were brushed with a camel-hair brush, like +the leaves in the solution of camphor, but this produced no effect. +</p> + +<p class="footnote"> +* See Dr. M. Traube’s curious experiments on the production of artificial +cells, and on their permeability to various salts, described in his papers: +“Experimente zur Theorie der Zellenbildung und Endosmose,” Breslau, +1866; and “Experimente zur physicalischen Erklrung der Bildung der +Zellhaut, ihres Wachsthums durch Intussusception,” Breslau, 1874. These +researches perhaps explain my results. Dr. Traube commonly employed as a +membrane the precipitate formed when tannic acid comes into contact with a +solution of gelatine. By allowing a precipitation of sulphate of barium to take +place at the same time, the membrane becomes “infiltrated” with +this salt; and in consequence of the intercalation of molecules of sulphate of +barium among those of the gelatine precipitate, the molecular interstices in +the membrane are made smaller. In this altered condition, the membrane no +longer allows the passage through it of either sulphate of ammonia or nitrate +of barium, though it retains its permeability for water and chloride of +ammonia. [page 217] +</p> + +<p> +Nor did these four leaves, on being left for 24 hrs. in the diluted alcohol, +undergo any inflection. They were then removed; one being placed in an infusion +of raw meat, and bits of meat on the discs of the other three, with their +stalks in water. Next day one seemed a little injured, whilst two others showed +merely a trace of inflection. We must, however, bear in mind that immersion for +24 hrs. in water prevents leaves from clasping meat. Hence alcohol of the above +strength is not poisonous, nor does it stimulate the leaves like camphor does. +</p> + +<p> +The vapour of alcohol acts differently. A plant having three good leaves was +left for 25 m. under a receiver holding 19 oz. with sixty minims of alcohol in +a watch-glass. No movement ensued, but some few of the glands were blackened +and shrivelled, whilst many became quite pale. These were scattered over all +the leaves in the most irregular manner, reminding me of the manner in which +the glands were affected by the vapour of carbonate of ammonia. Immediately on +the removal of the receiver particles of raw meat were placed on many of the +glands, those which retained their proper colour being chiefly selected. But +not a single tentacle was inflected during the next 4 hrs. After the first 2 +hrs. the glands on all the tentacles began to dry; and next morning, after 22 +hrs., all three leaves appeared almost dead, with their glands dry; the +tentacles on one leaf alone being partially inflected. +</p> + +<p> +A second plant was left for only 5 m. with some alcohol in a watch-glass, under +a 12-oz. receiver, and particles of meat were then placed on the glands of +several tentacles. After 10 m. some of them began to curve inwards, and after +55 m. nearly all were considerably inflected; but a few did not move. Some +anaesthetic effect is here probable, but by no means certain. A third plant was +also left for 5 m. under the same small vessel, with its whole inner surface +wetted with about a dozen drops of alcohol. Particles of meat were now placed +on the glands of several tentacles, some of which first began to move in 25 m.; +after 40 m. most of them were somewhat inflected, and after 1 hr. 10 m. almost +all were considerably inflected. From their slow rate of movement there can be +no doubt that the glands of these tentacles had been rendered insensible for a +time by exposure during 5 m. to the vapour of alcohol. +</p> + +<p> +Vapour of Chloroform.—The action of this vapour on Drosera is very +variable, depending, I suppose, on the constitution or age of the plant, or on +some unknown condition. It sometimes causes the tentacles to move with +extraordinary rapidity, and sometimes produces no such effect. The glands are +sometimes [page 218] rendered for a time insensible to the action of raw meat, +but sometimes are not thus affected, or in a very slight degree. A plant +recovers from a small dose, but is easily killed by a larger one. +</p> + +<p> +A plant was left for 30 m. under a bell-glass holding 19 fluid oz. (539.6 ml.) +with eight drops of chloroform, and before the cover was removed, most of the +tentacles became much inflected, though they did not reach the centre. After +the cover was removed, bits of meat were placed on the glands of several of the +somewhat incurved tentacles; these glands were found much blackened after 6 +hrs. 30 m., but no further movement ensued. After 24 hrs. the leaves appeared +almost dead. +</p> + +<p> +A smaller bell-glass, holding 12 fluid oz. (340.8 ml.), was now employed, and a +plant was left for 90 s. under it, with only two drops of chloroform. +Immediately on the removal of the glass all the tentacles curved inwards so as +to stand perpendicularly up; and some of them could actually be seen moving +with extraordinary quickness by little starts, and therefore in an unnatural +manner; but they never reached the centre. After 22 hrs. they fully +re-expanded, and on meat being placed on their glands, or when roughly touched +by a needle, they promptly became inflected; so that these leaves had not been +in the least injured. +</p> + +<p> +Another plant was placed under the same small bell-glass with three drops of +chloroform, and before two minutes had elapsed, the tentacles began to curl +inwards with rapid little jerks. The glass was then removed, and in the course +of two or three additional minutes almost every tentacle reached the centre. On +several other occasions the vapour did not excite any movement of this kind. +</p> + +<p> +There seems also to be great variability in the degree and manner in which +chloroform renders the glands insensible to the subsequent action of meat. In +the plant last referred to, which had been exposed for 2 m. to three drops of +chloroform, some few tentacles curved up only to a perpendicular position, and +particles of meat were placed on their glands; this caused them in 5 m. to +begin moving, but they moved so slowly that they did not reach the centre until +1 hr. 30 m. had elapsed. Another plant was similarly exposed, that is, for 2 m. +to three drops of chloroform, and on particles of meat being placed on the +glands of several tentacles, which had curved up into a perpendicular position, +one of these began to bend in 8 m., but afterwards moved very slowly; whilst +none of the other tentacles [page 219] moved for the next 40 m. Nevertheless, +in 1 hr. 45 m. from the time when the bits of meat had been given, all the +tentacles reached the centre. In this case some slight anaesthetic effect +apparently had been produced. On the following day the plant had perfectly +recovered. +</p> + +<p> +Another plant bearing two leaves was exposed for 2 m. under the 19-oz. vessel +to two drops of chloroform; it was then taken out and examined; again exposed +for 2 m. to two drops; taken out, and re-exposed for 3 m. to three drops; so +that altogether it was exposed alternately to the air and during 7 m. to the +vapour of seven drops of chloroform. Bits of meat were now placed on thirteen +glands on the two leaves. On one of these leaves, a single tentacle first began +moving in 40 m., and two others in 54 m. On the second leaf some tentacles +first moved in 1 hr. 11 m. After 2 hrs. many tentacles on both leaves were +inflected; but none had reached the centre within this time. In this case there +could not be the least doubt that the chloroform had exerted an anaesthetic +influence on the leaves. +</p> + +<p> +On the other hand, another plant was exposed under the same vessel for a much +longer time, viz. 20 m., to twice as much chloroform. Bits of meat were then +placed on the glands of many tentacles, and all of them, with a single +exception, reached the centre in from 13 m. to 14 m. In this case, little or no +anaesthetic effect had been produced; and how to reconcile these discordant +results, I know not. +</p> + +<p> +Vapour of Sulphuric Ether.—A plant was exposed for 30 m. to thirty minims +of this ether in a vessel holding 19 oz.; and bits of raw meat were afterwards +placed on many glands which had become pale-coloured; but none of the tentacles +moved. After 6 hrs. 30 m. the leaves appeared sickly, and the discal glands +were almost dry. By the next morning many of the tentacles were dead, as were +all those on which meat had been placed; showing that matter had been absorbed +from the meat which had increased the evil effects of the vapour. After four +days the plant itself died. Another plant was exposed in the same vessel for 15 +m. to forty minims. One young, small, and tender leaf had all its tentacles +inflected, and seemed much injured. Bits of raw meat were placed on several +glands on two other and older leaves. These glands became dry after 6 hrs.; and +seemed injured; the tentacles never moved, excepting one which was ultimately a +little inflected. The glands of the other tentacles continued to secrete, and +appeared uninjured, but the whole plant after three days became very sickly. +[page 220] +</p> + +<p> +In the two foregoing experiments the doses were evidently too large and +poisonous. With weaker doses, the anaesthetic effect was variable, as in the +case of chloroform. A plant was exposed for 5 m. to ten drops under a 12-oz. +vessel, and bits of meat were then placed on many glands. None of the tentacles +thus treated began to move in a decided manner until 40 m. had elapsed; but +then some of them moved very quickly, so that two reached the centre after an +additional interval of only 10 m. In 2 hrs. 12 m. from the time when the meat +was given, all the tentacles reached the centre. Another plant, with two +leaves, was exposed in the same vessel for 5 m. to a rather larger dose of +ether, and bits of meat were placed on several glands. In this case one +tentacle on each leaf began to bend in 5 m.; and after 12 m. two tentacles on +one leaf, and one on the second leaf, reached the centre. In 30 m. after the +meat had been given, all the tentacles, both those with and without meat, were +closely inflected; so that the ether apparently had stimulated these leaves, +causing all the tentacles to bend. +</p> + +<p> +Vapour of Nitric Ether.—This vapour seems more injurious than that of +sulphuric ether. A plant was exposed for 5 m. in a 12-oz. vessel to eight drops +in a watch-glass, and I distinctly saw a few tentacles curling inwards before +the glass was removed. Immediately afterwards bits of meat were placed on three +glands, but no movement ensued in the course of 18 m. The same plant was placed +again under the same vessel for 16 m. with ten drops of the ether. None of the +tentacles moved, and next morning those with the meat were still in the same +position. After 48 hrs. one leaf seemed healthy, but the others were much +injured. +</p> + +<p> +Another plant, having two good leaves, was exposed for 6 m. under a 19-oz. +vessel to the vapour from ten minims of the ether, and bits of meat were then +placed on the glands of many tentacles on both leaves. After 36 m. several of +them on one leaf became inflected, and after 1 hr. almost all the tentacles, +those with and without meat, nearly reached the centre. On the other leaf the +glands began to dry in 1 hr. 40 m., and after several hours not a single +tentacle was inflected; but by the next morning, after 21 hrs., many were +inflected, though they seemed much injured. In this and the previous +experiment, it is doubtful, owing to the injury which the leaves had suffered, +whether any anaesthetic effect had been produced. +</p> + +<p> +A third plant, having two good leaves, was exposed for only 4 m. in the 19-oz. +vessel to the vapour from six drops. Bits of meat were then placed on the +glands of seven tentacles on the [page 221] same leaf. A single tentacle moved +after 1 hr. 23 m.; after 2 hrs. 3 m. several were inflected; and after 3 hrs. 3 +m. all the seven tentacles with meat were well inflected. From the slowness of +these movements it is clear that this leaf had been rendered insensible for a +time to the action of the meat. A second leaf was rather differently affected; +bits of meat were placed on the glands of five tentacles, three of which were +slightly inflected in 28 m.; after 1 hr. 21 m. one reached the centre, but the +other two were still only slightly inflected; after 3 hrs. they were much more +inflected; but even after 5 hrs. 16 m. all five had not reached the centre. +Although some of the tentacles began to move moderately soon, they afterwards +moved with extreme slowness. By next morning, after 20 hrs., most of the +tentacles on both leaves were closely inflected, but not quite regularly. After +48 hrs. neither leaf appeared injured, though the tentacles were still +inflected; after 72 hrs. one was almost dead, whilst the other was re-expanding +and recovering. +</p> + +<p> +Carbonic Acid.—A plant was placed under a 122-oz. bell-glass filled with +this gas and standing over water; but I did not make sufficient allowance for +the absorption of the gas by the water, so that towards the latter part of the +experiment some air was drawn in. After an exposure of 2 hrs. the plant was +removed, and bits of raw meat placed on the glands of three leaves. One of +these leaves hung a little down, and was at first partly and soon afterwards +completely covered by the water, which rose within the vessel as the gas was +absorbed. On this latter leaf the tentacles, to which meat had been given, +became well inflected in 2 m. 30 s., that is, at about the normal rate; so that +until I remembered that the leaf had been protected from the gas, and might +perhaps have absorbed oxygen from the water which was continually drawn +inwards, I falsely concluded that the carbonic acid had produced no effect. On +the other two leaves, the tentacles with meat behaved very differently from +those on the first leaf; two of them first began to move slightly in 1 hr. 50 +m., always reckoning from the time when the meat was placed on the +glands—were plainly inflected in 2 hrs. 22 m.—and in 3 hrs 22 m. +reached the centre. Three other tentacles did not begin to move until 2 hrs. 20 +m. had elapsed, but reached the centre at about the same time with the others, +viz. in 3 hrs. 22 m. +</p> + +<p> +This experiment was repeated several times with nearly the same results, +excepting that the interval before the tentacles began to move varied a little. +I will give only one other case. [page 222] A plant was exposed in the same +vessel to the gas for 45 m., and bits of meat were then placed on four glands. +But the tentacles did not move for 1 hr. 40 m.; after 2 hrs. 30 m. all four +were well inflected, and after 3 hrs. reached the centre. +</p> + +<p> +The following singular phenomenon sometimes, but by no means always, occurred. +A plant was immersed for 2 hrs., and bits of meat were then placed on several +glands. In the course of 13 m. all the submarginal tentacles on one leaf became +considerably inflected; those with the meat not in the least degree more than +the others. On a second leaf, which was rather old, the tentacles with meat, as +well as a few others, were moderately inflected. On a third leaf all the +tentacles were closely inflected, though meat had not been placed on any of the +glands. This movement, I presume, may be attributed to excitement from the +absorption of oxygen. The last-mentioned leaf, to which no meat had been given, +was fully re-expanded after 24 hrs.; whereas the two other leaves had all their +tentacles closely inflected over the bits of meat which by this time had been +carried to their centres. Thus these three leaves had perfectly recovered from +the effects of the gas in the course of 24 hrs. +</p> + +<p> +On another occasion some fine plants, after having been left for 2 hrs. in the +gas, were immediately given bits of meat in the usual manner, and on their +exposure to the air most of their tentacles became in 12 m. curved into a +vertical or sub-vertical position, but in an extremely irregular manner; some +only on one side of the leaf and some on the other. They remained in this +position for some time; the tentacles with the bits of meat not having at first +moved more quickly or farther inwards than the others without meat. But after 2 +hrs. 20 m. the former began to move, and steadily went on bending until they +reached the centre. Next morning, after 22 hrs., all the tentacles on these +leaves were closely clasped over the meat which had been carried to their +centres; whilst the vertical and sub-vertical tentacles on the other leaves to +which no meat had been given had fully re-expanded. Judging, however, from the +subsequent action of a weak solution of carbonate of ammonia on one of these +latter leaves, it had not perfectly recovered its excitability and power of +movement in 22 hrs.; but another leaf, after an additional 24 hrs., had +completely recovered, judging from the manner in which it clasped a fly placed +on its disc. +</p> + +<p> +I will give only one other experiment. After the exposure of a plant for 2 hrs. +to the gas, one of its leaves was immersed in a rather strong solution of +carbonate of ammonia, together with [page 223] a fresh leaf from another plant. +The latter had most of its tentacles strongly inflected within 30 m.; whereas +the leaf which had been exposed to the carbonic acid remained for 24 hrs. in +the solution without undergoing any inflection, with the exception of two +tentacles. This leaf had been almost completely paralysed, and was not able to +recover its sensibility whilst still in the solution, which from having been +made with distilled water probably contained little oxygen.] +</p> + +<p> +Concluding Remarks on the Effects of the foregoing Agents.—As the glands, +when excited, transmit some influence to the surrounding tentacles, causing +them to bend and their glands to pour forth an increased amount of modified +secretion, I was anxious to ascertain whether the leaves included any element +having the nature of nerve-tissue, which, though not continuous, served as the +channel of transmission. This led me to try the several alkaloids and other +substances which are known to exert a powerful influence on the nervous system +of animals; I was at first encouraged in my trials by finding that strychnine, +digitaline, and nicotine, which all act on the nervous system, were poisonous +to Drosera, and caused a certain amount of inflection. Hydrocyanic acid, again, +which is so deadly a poison to animals, caused rapid movement of the tentacles. +But as several innocuous acids, though much diluted, such as benzoic, acetic, +&c., as well as some essential oils, are extremely poisonous to Drosera, +and quickly cause strong inflection, it seems probable that strychnine, +nicotine, digitaline, and hydrocyanic acid, excite inflection by acting on +elements in no way analogous to the nerve-cells of animals. If elements of this +latter nature had been present in the leaves, it might have been expected that +morphia, hyoscyamus, atropine, veratrine, colchicine, curare, and diluted +alcohol would have produced some marked effect; whereas [page 224] these +substances are not poisonous and have no power, or only a very slight one, of +inducing inflection. It should, however, be observed that curare, colchicine, +and veratrine are muscle-poisons—that is, act on nerves having some +special relation with the muscles, and, therefore, could not be expected to act +on Drosera. The poison of the cobra is most deadly to animals, by paralysing +their nerve-centres,* yet is not in the least so to Drosera, though quickly +causing strong inflection. +</p> + +<p> +Notwithstanding the foregoing facts, which show how widely different is the +effect of certain substances on the health or life of animals and of Drosera, +yet there exists a certain degree of parallelism in the action of certain other +substances. We have seen that this holds good in a striking manner with the +salts of sodium and potassium. Again, various metallic salts and acids, namely +those of silver, mercury, gold, tin, arsenic, chromium, copper, and platina, +most or all of which are highly poisonous to animals, are equally so to +Drosera. But it is a singular fact that the chloride of lead and two salts of +barium were not poisonous to this plant. It is an equally strange fact, that, +though acetic and propionic acids are highly poisonous, their ally, formic +acid, is not so; and that, whilst certain vegetable acids, namely oxalic, +benzoic, &c., are poisonous in a high degree, gallic, tannic, tartaric, and +malic (all diluted to an equal degree) are not so. Malic acid induces +inflection, whilst the three other just named vegetable acids have no such +power. But a pharmacopoeia would be requisite to describe the diversified +effects of various substances on Drosera.** +</p> + +<p class="footnote"> +* Dr. Fayrer, ‘The Thanatophidia of India,’ 1872, p. 4. +</p> + +<p class="footnote"> +** Seeing that acetic, hydrocyanic, and chromic acids, acetate of strychnine, +and vapour of ether, are poisonous to Drosera, [[page 225]] it is remarkable +that Dr. Ransom (‘Philosoph. Transact.’ 1867, p. 480), who used +much stronger solutions of these substances than I did, states “that the +rhythmic contractility of the yolk (of the ova of the pike) is not materially +influenced by any of the poisons used, which did not act chemically, with the +exception of chloroform and carbonic acid.” I find it stated by several +writers that curare has no influence on sarcode or protoplasm, and we have seen +that, though curare excites some degree of inflection, it causes very little +aggregation of the protoplasm.) [page 226] +</p> + +<p> +Of the alkaloids and their salts which were tried, several had not the least +power of inducing inflection; others, which were certainly absorbed, as shown +by the changed colour of the glands, had but a very moderate power of this +kind; others, again, such as the acetate of quinine and digitaline, caused +strong inflection. +</p> + +<p> +The several substances mentioned in this chapter affect the colour of the +glands very differently. These often become dark at first, and then very pale +or white, as was conspicuously the case with glands subjected to the poison of +the cobra and citrate of strychnine. In other cases they are from the first +rendered white, as with leaves placed in hot water and several acids; and this, +I presume, is the result of the coagulation of the albumen. On the same leaf +some glands become white and others dark-coloured, as occurred with leaves in a +solution of the sulphate of quinine, and in the vapour of alcohol. Prolonged +immersion in nicotine, curare, and even water, blackens the glands; and this, I +believe, is due to the aggregation of the protoplasm within their cells. Yet +curare caused very little aggregation in the cells of the tentacles, whereas +nicotine and sulphate of quinine induced strongly marked aggregation down their +bases. The aggregated masses in leaves which had been immersed for 3 hrs. 15 m. +in a saturated solution of sulphate of quinine exhibited incessant [page 226] +changes of form, but after 24 hrs. were motionless; the leaf being flaccid and +apparently dead. On the other hand, with leaves subjected for 48 hrs. to a +strong solution of the poison of the cobra, the protoplasmic masses were +unusually active, whilst with the higher animals the vibratile cilia and white +corpuscles of the blood seem to be quickly paralysed by this substance. +</p> + +<p> +With the salts of alkalies and earths, the nature of the base, and not that of +the acid, determines their physiological action on Drosera, as is likewise the +case with animals; but this rule hardly applies to the salts of quinine and +strychnine, for the acetate of quinine causes much more inflection than the +sulphate, and both are poisonous, whereas the nitrate of quinine is not +poisonous, and induces inflection at a much slower rate than the acetate. The +action of the citrate of strychnine is also somewhat different from that of the +sulphate. +</p> + +<p> +Leaves which have been immersed for 24 hrs. in water, and for only 20 m. in +diluted alcohol, or in a weak solution of sugar, are afterwards acted on very +slowly, or not at all, by the phosphate of ammonia, though they are quickly +acted on by the carbonate. Immersion for 20 m. in a solution of gum arabic has +no such inhibitory power. The solutions of certain salts and acids affect the +leaves, with respect to the subsequent action of the phosphate, exactly like +water, whilst others allow the phosphate afterwards to act quickly and +energetically. In this latter case, the interstices of the cell-walls may have +been blocked up by the molecules of the salts first given in solution, so that +water could not afterwards enter, though the molecules of the phosphate could +do so, and those of the carbonate still more easily. [page 227] +</p> + +<p> +The action of camphor dissolved in water is remarkable, for it not only soon +induces inflection, but apparently renders the glands extremely sensitive to +mechanical irritation; for if they are brushed with a soft brush, after being +immersed in the solution for a short time, the tentacles begin to bend in about +2 m. It may, however, be that the brushing, though not a sufficient stimulus by +itself, tends to excite movement merely by reinforcing the direct action of the +camphor. The vapour of camphor, on the other hand, serves as a narcotic. +</p> + +<p> +Some essential oils, both in solution and in vapour, cause rapid inflection, +others have no such power; those which I tried were all poisonous. +</p> + +<p> +Diluted alcohol (one part to seven of water) is not poisonous, does not induce +inflection, nor increase the sensitiveness of the glands to mechanical +irritation. The vapour acts as a narcotic or anaesthetic, and long exposure to +it kills the leaves. +</p> + +<p> +The vapours of chloroform, sulphuric and nitric ether, act in a singularly +variable manner on different leaves, and on the several tentacles of the same +leaf. This, I suppose, is owing to differences in the age or constitution of +the leaves, and to whether certain tentacles have lately been in action. That +these vapours are absorbed by the glands is shown by their changed colour; but +as other plants not furnished with glands are affected by these vapours, it is +probable that they are likewise absorbed by the stomata of Drosera. They +sometimes excite extraordinarily rapid inflection, but this is not an +invariable result. If allowed to act for even a moderately long time, they kill +the leaves; whilst a small dose acting for only a short time serves as a +narcotic or anaesthetic. In this case the tentacles, whether or not they have +[page 228] become inflected, are not excited to further movement by bits of +meat placed on the glands, until some considerable time has elapsed. It is +generally believed that with animals and plants these vapours act by arresting +oxidation. +</p> + +<p> +Exposure to carbonic acid for 2 hrs., and in one case for only 45 m., likewise +rendered the glands insensible for a time to the powerful stimulus of raw meat. +The leaves, however, recovered their full powers, and did not seem in the least +injured, on being left in the air for 24 or 48 hrs. We have seen in the third +chapter that the process of aggregation in leaves subjected for two hours to +this gas and then immersed in a solution of the carbonate of ammonia is much +retarded, so that a considerable time elapses before the protoplasm in the +lower cells of the tentacles becomes aggregated. In some cases, soon after the +leaves were removed from the gas and brought into the air, the tentacles moved +spontaneously; this being due, I presume, to the excitement from the access of +oxygen. These inflected tentacles, however, could not be excited for some time +afterwards to any further movement by their glands being stimulated. With other +irritable plants it is known* that the exclusion of oxygen prevents their +moving, and arrests the movements of the protoplasm within their cells, but +this arrest is a different phenomenon from the retardation of the process of +aggregation just alluded to. Whether this latter fact ought to be attributed to +the direct action of the carbonic acid, or to the exclusion of oxygen, I know +not. +</p> + +<p class="footnote"> +* Sachs, ‘Traité de Bot.’ 1874, pp. 846, 1037. [page 229] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0010" id="link2HCH0010"></a> +CHAPTER X.<br/> +ON THE SENSITIVENESS OF THE LEAVES, AND ON THE LINES OF TRANSMISSION OF THE +MOTOR IMPULSE.</h2> + +<p class="letter"> +Glands and summits of the tentacles alone sensitive—Transmission of the +motor impulse down the pedicels of the tentacles, and across the blade of the +leaf—Aggregation of the protoplasm, a reflex action—First discharge +of the motor impulse sudden—Direction of the movements of the +tentacles—Motor impulse transmitted through the cellular tissue— +Mechanism of the movements—Nature of the motor impulse—Re-expansion +of the tentacles. +</p> + +<p> +We have seen in the previous chapters that many widely different stimulants, +mechanical and chemical, excite the movement of the tentacles, as well as of +the blade of the leaf; and we must now consider, firstly, what are the points +which are irritable or sensitive, and secondly how the motor impulse is +transmitted from one point to another. The glands are almost exclusively the +seat of irritability, yet this irritability must extend for a very short +distance below them; for when they were cut off with a sharp pair of scissors +without being themselves touched, the tentacles often became inflected. These +headless tentacles frequently re-expanded; and when afterwards drops of the two +most powerful known stimulants were placed on the cut-off ends, no effect was +produced. Nevertheless these headless tentacles are capable of subsequent +inflection if excited by an impulse sent from the disc. I succeeded on several +occasions in crushing glands between fine pincers, but this did not excite any +movement; nor did raw meat and salts of ammonia, when placed on such crushed +glands. [page 230] It is probable that they were killed so instantly that they +were not able to transmit any motor impulse; for in six observed cases (in two +of which however the gland was quite pinched off) the protoplasm within the +cells of the tentacles did not become aggregated; whereas in some adjoining +tentacles, which were inflected from having been roughly touched by the +pincers, it was well aggregated. In like manner the protoplasm does not become +aggregated when a leaf is instantly killed by being dipped into boiling water. +On the other hand, in several cases in which tentacles became inflected after +their glands had been cut off with sharp scissors, a distinct though moderate +degree of aggregation supervened. +</p> + +<p> +The pedicels of the tentacles were roughly and repeatedly rubbed; raw meat or +other exciting substances were placed on them, both on the upper surface near +the base and elsewhere, but no distinct movement ensued. Some bits of meat, +after being left for a considerable time on the pedicels, were pushed upwards, +so as just to touch the glands, and in a minute the tentacles began to bend. I +believe that the blade of the leaf is not sensitive to any stimulant. I drove +the point of a lancet through the blades of several leaves, and a needle three +or four times through nineteen leaves: in the former case no movement ensued; +but about a dozen of the leaves which were repeatedly pricked had a few +tentacles irregularly inflected. As, however, their backs had to be supported +during the operation, some of the outer glands, as well as those on the disc, +may have been touched; and this perhaps sufficed to cause the slight degree of +movement observed. Nitschke*says +</p> + +<p class="footnote"> +* ‘Bot. Zeitung,’ 1860, p. 234. [page 231] +</p> + +<p> +that cutting and pricking the leaf does not excite movement. The petiole of the +leaf is quite insensible. +</p> + +<p> +The backs of the leaves bear numerous minute papillae, which do not secrete, +but have the power of absorption. These papillae are, I believe, rudiments of +formerly existing tentacles together with their glands. Many experiments were +made to ascertain whether the backs of the leaves could be irritated in any +way, thirty-seven leaves being thus tried. Some were rubbed for a long time +with a blunt needle, and drops of milk and other exciting fluids, raw meat, +crushed flies, and various substances, placed on others. These substances were +apt soon to become dry, showing that no secretion had been excited. Hence I +moistened them with saliva, solutions of ammonia, weak hydrochloric acid, and +frequently with the secretion from the glands of other leaves. I also kept some +leaves, on the backs of which exciting objects had been placed, under a damp +bell-glass; but with all my care I never saw any true movement. I was led to +make so many trials because, contrary to my previous experience, Nitschke +states* that, after affixing objects to the backs of leaves by the aid of the +viscid secretion, he repeatedly saw the tentacles (and in one instance the +blade) become reflexed. This movement, if a true one, would be most anomalous; +for it implies that the tentacles receive a motor impulse from an unnatural +source, and have the power of bending in a direction exactly the reverse of +that which is habitual to them; this power not being of the least use to the +plant, as insects cannot adhere to the smooth backs of the leaves. +</p> + +<p> +I have said that no effect was produced in the above +</p> + +<p class="footnote"> +* ‘Bot. Zeitung.’ 1860, p. 437. [page 232] +</p> + +<p> +cases; but this is not strictly true, for in three instances a little syrup was +added to the bits of raw meat on the backs of leaves, in order to keep them +damp for a time; and after 36 hrs. there was a trace of reflexion in the +tentacles of one leaf, and certainly in the blade of another. After twelve +additional hours, the glands began to dry, and all three leaves seemed much +injured. Four leaves were then placed under a bell-glass, with their footstalks +in water, with drops of syrup on their backs, but without any meat. Two of +these leaves, after a day, had a few tentacles reflexed. The drops had now +increased considerably in size, from having imbibed moisture, so as to trickle +down the backs of the tentacles and footstalks. On the second day, one leaf had +its blade much reflexed; on the third day the tentacles of two were much +reflexed, as well as the blades of all four to a greater or less degree. The +upper side of one leaf, instead of being, as at first, slightly concave, now +presented a strong convexity upwards. Even on the fifth day the leaves did not +appear dead. Now, as sugar does not in the least excite Drosera, we may safely +attribute the reflexion of the blades and tentacles of the above leaves to +exosmose from the cells which were in contact with the syrup, and their +consequent contraction. When drops of syrup are placed on the leaves of plants +with their roots still in damp earth, no inflection ensues, for the roots, no +doubt, pump up water as quickly as it is lost by exosmose. But if cut-off +leaves are immersed in syrup, or in any dense fluid, the tentacles are greatly, +though irregularly, inflected, some of them assuming the shape of corkscrews; +and the leaves soon become flaccid. If they are now immersed in a fluid of low +specific gravity, the tentacles re-expand. From these [page 233] facts we may +conclude that drops of syrup placed on the backs of leaves do not act by +exciting a motor impulse which is transmitted to the tentacles; but that they +cause reflexion by inducing exosmose. Dr. Nitschke used the secretion for +sticking insects to the backs of the leaves; and I suppose that he used a large +quantity, which from being dense probably caused exosmose. Perhaps he +experimented on cut-off leaves, or on plants with their roots not supplied with +enough water. +</p> + +<p> +As far, therefore, as our present knowledge serves, we may conclude that the +glands, together with the immediately underlying cells of the tentacles, are +the exclusive seats of that irritability or sensitiveness with which the leaves +are endowed. The degree to which a gland is excited can be measured only by the +number of the surrounding tentacles which are inflected, and by the amount and +rate of their movement. Equally vigorous leaves, exposed to the same +temperature (and this is an important condition), are excited in different +degrees under the following circumstances. A minute quantity of a weak solution +produces no effect; add more, or give a rather stronger solution, and the +tentacles bend. Touch a gland once or twice, and no movement follows; touch it +three or four times, and the tentacle becomes inflected. But the nature of the +substance which is given is a very important element: if equal-sized particles +of glass (which acts only mechanically), of gelatine, and raw meat, are placed +on the discs of several leaves, the meat causes far more rapid, energetic, and +widely extended movement than the two former substances. The number of glands +which are excited also makes a great difference in the result: place a bit of +meat on one or two of the discal [page 234] glands, and only a few of the +immediately surrounding short tentacles are inflected; place it on several +glands, and many more are acted on; place it on thirty or forty, and all the +tentacles, including the extreme marginal ones, become closely inflected. We +thus see that the impulses proceeding from a number of glands strengthen one +another, spread farther, and act on a larger number of tentacles, than the +impulse from any single gland. +</p> + +<p> +Transmission of the Motor Impulse.—In every case the impulse from a gland +has to travel for at least a short distance to the basal part of the tentacle, +the upper part and the gland itself being merely carried by the inflection of +the lower part. The impulse is thus always transmitted down nearly the whole +length of the pedicel. When the central glands are stimulated, and the extreme +marginal tentacles become inflected, the impulse is transmitted across half the +diameter of the disc; and when the glands on one side of the disc are +stimulated, the impulse is transmitted across nearly the whole width of the +disc. A gland transmits its motor impulse far more easily and quickly down its +own tentacle to the bending place than across the disc to neighbouring +tentacles. Thus a minute dose of a very weak solution of ammonia, if given to +one of the glands of the exterior tentacles, causes it to bend and reach the +centre; whereas a large drop of the same solution, given to a score of glands +on the disc, will not cause through their combined influence the least +inflection of the exterior tentacles. Again, when a bit of meat is placed on +the gland of an exterior tentacle, I have seen movement in ten seconds, and +repeatedly within a minute; but a much larger bit placed on several glands on +the disc does not cause [page 235] the exterior tentacles to bend until half an +hour or even several hours have elapsed. +</p> + +<p> +The motor impulse spreads gradually on all sides from one or more excited +glands, so that the tentacles which stand nearest are always first affected. +Hence, when the glands in the centre of the disc are excited, the extreme +marginal tentacles are the last inflected. But the glands on different parts of +the leaf transmit their motor power in a somewhat different manner. If a bit of +meat be placed on the long-headed gland of a marginal tentacle, it quickly +transmits an impulse to its own bending portion; but never, as far as I have +observed, to the adjoining tentacles; for these are not affected until the meat +has been carried to the central glands, which then radiate forth their conjoint +impulse on all sides. On four occasions leaves were prepared by removing some +days previously all the glands from the centre, so that these could not be +excited by the bits of meat brought to them by the inflection of the marginal +tentacles; and now these marginal tentacles re-expanded after a time without +any other tentacle being affected. Other leaves were similarly prepared, and +bits of meat were placed on the glands of two tentacles in the third row from +the outside, and on the glands of two tentacles in the fifth row. In these four +cases the impulse was sent in the first place laterally, that is, in the same +concentric row of tentacles, and then towards the centre; but not +centrifugally, or towards the exterior tentacles. In one of these cases only a +single tentacle on each side of the one with meat was affected. In the three +other cases, from half a dozen to a dozen tentacles, both laterally and towards +the centre, were well inflected or sub-inflected. Lastly, in [page 236] ten +other experiments, minute bits of meat were placed on a single gland or on two +glands in the centre of the disc. In order that no other glands should touch +the meat, through the inflection of the closely adjoining short tentacles, +about half a dozen glands had been previously removed round the selected ones. +On eight of these leaves from sixteen to twenty-five of the short surrounding +tentacles were inflected in the course of one or two days; so that the motor +impulse radiating from one or two of the discal glands is able to produce this +much effect. The tentacles which had been removed are included in the above +numbers; for, from standing so close, they would certainly have been affected. +On the two remaining leaves, almost all the short tentacles on the disc were +inflected. With a more powerful stimulus than meat, namely a little phosphate +of lime moistened with saliva, I have seen the inflection spread still farther +from a single gland thus treated; but even in this case the three or four outer +rows of tentacles were not affected. From these experiments it appears that the +impulse from a single gland on the disc acts on a greater number of tentacles +than that from a gland of one of the exterior elongated tentacles; and this +probably follows, at least in part, from the impulse having to travel a very +short distance down the pedicels of the central tentacles, so that it is able +to spread to a considerable distance all round. +</p> + +<p> +Whilst examining these leaves, I was struck with the fact that in six, perhaps +seven, of them the tentacles were much more inflected at the distal and +proximal ends of the leaf (i.e. towards the apex and base) than on either side; +and yet the tentacles on the sides stood as near to the gland where the bit of +meat lay as did those at the two ends. It thus appeared as [page 237] if the +motor impulse was transmitted from the centre across the disc more readily in a +longitudinal than in a transverse direction; and as this appeared a new and +interesting fact in the physiology of plants, thirty-five fresh experiments +were made to test its truth. Minute bits of meat were placed on a single gland +or on a few glands, on the right or left side of the discs of eighteen leaves; +other bits of the same size being placed on the distal or proximal ends of +seventeen other leaves. Now if the motor impulse were transmitted with equal +force or at an equal rate through the blade in all directions, a bit of meat +placed at one side or at one end of the disc ought to affect equally all the +tentacles situated at an equal distance from it; but this certainly is not the +case. Before giving the general results, it may be well to describe three or +four rather unusual cases. +</p> + +<p> +[(1) A minute fragment of a fly was placed on one side of the disc, and after +32 m. seven of the outer tentacles near the fragment were inflected; after 10 +hrs. several more became so, and after 23 hrs. a still greater number; and now +the blade of the leaf on this side was bent inwards so as to stand up at right +angles to the other side. Neither the blade of the leaf nor a single tentacle +on the opposite side was affected; the line of separation between the two +halves extending from the footstalk to the apex. The leaf remained in this +state for three days, and on the fourth day began to re-expand; not a single +tentacle having been inflected on the opposite side. +</p> + +<p> +(2) I will here give a case not included in the above thirty-five experiments. +A small fly was found adhering by its feet to the left side of the disc. The +tentacles on this side soon closed in and killed the fly; and owing probably to +its struggle whilst alive, the leaf was so much excited that in about 24 hrs. +all the tentacles on the opposite side became inflected; but as they found no +prey, for their glands did not reach the fly, they re-expanded in the course of +15 hrs.; the tentacles on the left side remaining clasped for several days. +</p> + +<p> +(3) A bit of meat, rather larger than those commonly used, [page 238] was +placed in a medial line at the basal end of the disc, near the footstalk; after +2 hrs. 30 m. some neighbouring tentacles were inflected; after 6 hrs. the +tentacles on both sides of the footstalk, and some way up both sides, were +moderately inflected; after 8 hrs. the tentacles at the further or distal end +were more inflected than those on either side; after 23 hrs. the meat was well +clasped by all the tentacles, excepting by the exterior ones on the two sides. +</p> + +<p> +(4) Another bit of meat was placed at the opposite or distal end of another +leaf, with exactly the same relative results. +</p> + +<p> +(5) A minute bit of meat was placed on one side of the disc; next day the +neighbouring short tentacles were inflected, as well as in a slight degree +three or four on the opposite side near the footstalk. On the second day these +latter tentacles showed signs of re-expanding, so I added a fresh bit of meat +at nearly the same spot, and after two days some of the short tentacles on the +opposite side of the disc were inflected. As soon as these began to re-expand, +I added another bit of meat, and next day all the tentacles on the opposite +side of the disc were inflected towards the meat; whereas we have seen that +those on the same side were affected by the first bit of meat which was given.] +</p> + +<p> +Now for the general results. Of the eighteen leaves on which bits of meat were +placed on the right or left sides of the disc, eight had a vast number of +tentacles inflected on the same side, and in four of them the blade itself on +this side was likewise inflected; whereas not a single tentacle nor the blade +was affected on the opposite side. These leaves presented a very curious +appearance, as if only the inflected side was active, and the other paralysed. +In the remaining ten cases, a few tentacles became inflected beyond the medial +line, on the side opposite to that where the meat lay; but, in some of these +cases, only at the proximal or distal ends of the leaves. The inflection on the +opposite side always occurred considerably after that on the same side, and in +one instance not until the fourth day. We have also seen [page 239] with No. 5 +that bits of meat had to be added thrice before all the short tentacles on the +opposite side of the disc were inflected. +</p> + +<p> +The result was widely different when bits of meat were placed in a medial line +at the distal or proximal ends of the disc. In three of the seventeen +experiments thus made, owing either to the state of the leaf or to the +smallness of the bit of meat, only the immediately adjoining tentacles were +affected; but in the other fourteen cases the tentacles at the opposite end of +the leaf were inflected, though these were as distant from where the meat lay +as were those on one side of the disc from the meat on the opposite side. In +some of the present cases the tentacles on the sides were not at all affected, +or in a less degree, or after a longer interval of time, than those at the +opposite end. One set of experiments is worth giving in fuller detail. Cubes of +meat, not quite so small as those usually employed, were placed on one side of +the discs of four leaves, and cubes of the same size at the proximal or distal +end of four other leaves. Now, when these two sets of leaves were compared +after an interval of 24 hrs., they presented a striking difference. Those +having the cubes on one side were very slightly affected on the opposite side; +whereas those with the cubes at either end had almost every tentacle at the +opposite end, even the marginal ones, closely inflected. After 48 hrs. the +contrast in the state of the two sets was still great; yet those with the meat +on one side now had their discal and submarginal tentacles on the opposite side +somewhat inflected, this being due to the large size of the cubes. Finally we +may conclude from these thirty-five experiments, not to mention the six or +seven previous ones, that the motor impulse is transmitted from any single +gland [page 240] or small group of glands through the blade to the other +tentacles more readily and effectually in a longitudinal than in a transverse +direction. +</p> + +<p> +As long as the glands remain excited, and this may last for many days, even for +eleven, as when in contact with phosphate of lime, they continue to transmit a +motor impulse to the basal and bending parts of their own pedicels, for +otherwise they would re-expand. The great difference in the length of time +during which tentacles remain inflected over inorganic objects, and over +objects of the same size containing soluble nitrogenous matter, proves the same +fact. But the intensity of the impulse transmitted from an excited gland, which +has begun to pour forth its acid secretion and is at the same time absorbing, +seems to be very small compared with that which it transmits when first +excited. Thus, when moderately large bits of meat were placed on one side of +the disc, and the discal and sub-marginal tentacles on the opposite side became +inflected, so that their glands at last touched the meat and absorbed matter +from it, they did not transmit any motor influence to the exterior rows of +tentacles on the same side, for these never became inflected. If, however, meat +had been placed on the glands of these same tentacles before they had begun to +secrete copiously and to absorb, they undoubtedly would have affected the +exterior rows. Nevertheless, when I gave some phosphate of lime, which is a +most powerful stimulant, to several submarginal tentacles already considerably +inflected, but not yet in contact with some phosphate previously placed on two +glands in the centre of the disc, the exterior tentacles on the same side were +acted on. +</p> + +<p> +When a gland is first excited, the motor impulse is discharged within a few +seconds, as we know from the [page 241] bending of the tentacle; and it appears +to be discharged at first with much greater force than afterwards. Thus, in the +case above given of a small fly naturally caught by a few glands on one side of +a leaf, an impulse was slowly transmitted from them across the whole breadth of +the leaf, causing the opposite tentacles to be temporarily inflected, but the +glands which remained in contact with the insect, though they continued for +several days to send an impulse down their own pedicels to the bending place, +did not prevent the tentacles on the opposite side from quickly re-expanding; +so that the motor discharge must at first have been more powerful than +afterwards. +</p> + +<p> +When an object of any kind is placed on the disc, and the surrounding tentacles +are inflected, their glands secrete more copiously and the secretion becomes +acid, so that some influence is sent to them from the discal glands. This +change in the nature and amount of the secretion cannot depend on the bending +of the tentacles, as the glands of the short central tentacles secrete acid +when an object is placed on them, though they do not themselves bend. Therefore +I inferred that the glands of the disc sent some influence up the surrounding +tentacles to their glands, and that these reflected back a motor impulse to +their basal parts; but this view was soon proved erroneous. It was found by +many trials that tentacles with their glands closely cut off by sharp scissors +often become inflected and again re-expand, still appearing healthy. One which +was observed continued healthy for ten days after the operation. I therefore +cut the glands off twenty-five tentacles, at different times and on different +leaves, and seventeen of these soon became inflected, and afterwards +re-expanded. The re-expansion commenced in about [page 242] 8 hrs. or 9 hrs., +and was completed in from 22 hrs. to 30 hrs. from the time of inflection. After +an interval of a day or two, raw meat with saliva was placed on the discs of +these seventeen leaves, and when observed next day, seven of the headless +tentacles were inflected over the meat as closely as the uninjured ones on the +same leaves; and an eighth headless tentacle became inflected after three +additional days. The meat was removed from one of these leaves, and the surface +washed with a little stream of water, and after three days the headless +tentacle re-expanded for the second time. These tentacles without glands were, +however, in a different state from those provided with glands and which had +absorbed matter from the meat, for the protoplasm within the cells of the +former had undergone far less aggregation. From these experiments with headless +tentacles it is certain that the glands do not, as far as the motor impulse is +concerned, act in a reflex manner like the nerve-ganglia of animals. +</p> + +<p> +But there is another action, namely that of aggregation, which in certain cases +may be called reflex, and it is the only known instance in the vegetable +kingdom. We should bear in mind that the process does not depend on the +previous bending of the tentacles, as we clearly see when leaves are immersed +in certain strong solutions. Nor does it depend on increased secretion from the +glands, and this is shown by several facts, more especially by the papillae, +which do not secrete, yet undergoing aggregation, if given carbonate of ammonia +or an infusion of raw meat. When a gland is directly stimulated in any way, as +by the pressure of a minute particle of glass, the protoplasm within the cells +of the gland first becomes aggregated, then that in the cells immediately +beneath the gland, and so lower and lower down the tentacles to their +bases;— [page 243] that is, if the stimulus has been sufficient and not +injurious. Now, when the glands of the disc are excited, the exterior tentacles +are affected in exactly the same manner: the aggregation always commences in +their glands, though these have not been directly excited, but have only +received some influence from the disc, as shown by their increased acid +secretion. The protoplasm within the cells immediately beneath the glands are +next affected, and so downwards from cell to cell to the bases of the +tentacles. This process apparently deserves to be called a reflex action, in +the same manner as when a sensory nerve is irritated, and carries an impression +to a ganglion which sends back some influence to a muscle or gland, causing +movement or increased secretion; but the action in the two cases is probably of +a widely different nature. After the protoplasm in a tentacle has been +aggregated, its redissolution always begins in the lower part, and slowly +travels up the pedicel to the gland, so that the protoplasm last aggregated is +first redissolved. This probably depends merely on the protoplasm being less +and less aggregated, lower and lower down in the tentacles, as can be seen +plainly when the excitement has been slight. As soon, therefore, as the +aggregating action altogether ceases, redissolution naturally commences in the +less strongly aggregated matter in the lowest part of the tentacle, and is +there first completed. +</p> + +<p> +Direction of the Inflected Tentacles.—When a particle of any kind is +placed on the gland of one of the outer tentacles, this invariably moves +towards the centre of the leaf; and so it is with all the tentacles of a leaf +immersed in any exciting fluid. The glands of the exterior tentacles then form +a ring round the middle part of the disc, as shown in a previous figure (fig. +4, [page 244] p. 10). The short tentacles within this ring still retain their +vertical position, as they likewise do when a large object is placed on their +glands, or when an insect is caught by them. In this latter case we can see +that the inflection of the short central tentacles would be useless, as their +glands are already in contact with their prey. +</p> + +<p> +FIG. 10. (Drosera rotundifolia.) Leaf (enlarged) with the tentacles inflected +over a bit of meat placed on one side of the disc. +</p> + +<p> +The result is very different when a single gland on one side of the disc is +excited, or a few in a group. These send an impulse to the surrounding +tentacles, which do not now bend towards the centre of the leaf, but to the +point of excitement. We owe this capital observation to Nitschke,* and since +reading his paper a few years ago, I have repeatedly verified it. If a minute +bit of meat be placed by the aid of a needle on a single gland, or on three or +four together, halfway between the centre and the circumference of the disc, +the directed movement of the surrounding tentacles is well exhibited. An +accurate drawing of a leaf with meat in this position is here reproduced (fig. +10), and we see the tentacles, including some of the exterior ones, accurately +directed to the point where the meat lay. But a much better +</p> + +<p class="footnote"> +* ‘Bot. Zeitung,’ 1860, p. 240. [page 245] +</p> + +<p> +plan is to place a particle of the phosphate of lime moistened with saliva on a +single gland on one side of the disc of a large leaf, and another particle on a +single gland on the opposite side. In four such trials the excitement was not +sufficient to affect the outer tentacles, but all those near the two points +were directed to them, so that two wheels were formed on the disc of the same +leaf; the pedicels of the tentacles forming the spokes, and the glands united +in a mass over the phosphate representing the axles. The precision with which +each tentacle pointed to the particle was wonderful; so that in some cases I +could detect no deviation from perfect accuracy. Thus, although the short +tentacles in the middle of the disc do not bend when their glands are excited +in a direct manner, yet if they receive a motor impulse from a point on one +side, they direct themselves to the point equally well with the tentacles on +the borders of the disc. +</p> + +<p> +In these experiments, some of the short tentacles on the disc, which would have +been directed to the centre, had the leaf been immersed in an exciting fluid, +were now inflected in an exactly opposite direction, viz. towards the +circumference. These tentacles, therefore, had deviated as much as 180o from +the direction which they would have assumed if their own glands had been +stimulated, and which may be considered as the normal one. Between this, the +greatest possible and no deviation from the normal direction, every degree +could be observed in the tentacles on these several leaves. Notwithstanding the +precision with which the tentacles generally were directed, those near the +circumference of one leaf were not accurately directed towards some phosphate +of lime at a rather distant point on the opposite side of the disc. It appeared +as if the motor [page 246] impulse in passing transversely across nearly the +whole width of the disc had departed somewhat from a true course. This accords +with what we have already seen of the impulse travelling less readily in a +transverse than in a longitudinal direction. In some other cases, the exterior +tentacles did not seem capable of such accurate movement as the shorter and +more central ones. +</p> + +<p> +Nothing could be more striking than the appearance of the above four leaves, +each with their tentacles pointing truly to the two little masses of the +phosphate on their discs. We might imagine that we were looking at a lowly +organised animal seizing prey with its arms. In the case of Drosera the +explanation of this accurate power of movement, no doubt, lies in the motor +impulse radiating in all directions, and whichever side of a tentacle it first +strikes, that side contracts, and the tentacle consequently bends towards the +point of excitement. The pedicels of the tentacles are flattened, or elliptic +in section. Near the bases of the short central tentacles, the flattened or +broad face is formed of about five longitudinal rows of cells; in the outer +tentacles of the disc it consists of about six or seven rows; and in the +extreme marginal tentacles of above a dozen rows. As the flattened bases are +thus formed of only a few rows of cells, the precision of the movements of the +tentacles is the more remarkable; for when the motor impulse strikes the base +of a tentacle in a very oblique direction relatively to its broad face, +scarcely more than one or two cells towards one end can be affected at first, +and the contraction of these cells must draw the whole tentacle into the proper +direction. It is, perhaps, owing to the exterior pedicels being much flattened +that they do not bend quite so accurately to the point of excitement as the +[page 247] more central ones. The properly directed movement of the tentacles +is not an unique case in the vegetable kingdom, for the tendrils of many plants +curve towards the side which is touched; but the case of Drosera is far more +interesting, as here the tentacles are not directly excited, but receive an +impulse from a distant point; nevertheless, they bend accurately towards this +point. +</p> + +<p> +FIG. 11. (Drosera rotundifolia.) Diagram showing the distribution of the +vascular tissue in a small leaf. +</p> + +<p> +On the Nature of the Tissues through which the Motor Impulse is +Transmitted.—It will be necessary first to describe briefly the course of +the main fibro-vascular bundles. These are shown in the accompanying sketch +(fig. 11) of a small leaf. Little vessels from the neighbouring bundles enter +all the many tentacles with which the surface is studded; but these are not +here represented. The central trunk, which runs up the footstalk, bifurcates +near the centre of the leaf, each branch bifurcating again and again according +to the size of the leaf. This central trunk sends off, low down on each side, a +delicate branch, which may be called the sublateral branch. There is also, on +each side, a main lateral branch or bundle, which bifurcates in the same manner +as the others. Bifurcation does not imply that any single vessel divides, but +that a bundle [page 248] divides into two. By looking to either side of the +leaf, it will be seen that a branch from the great central bifurcation +inosculates with a branch from the lateral bundle, and that there is a smaller +inosculation between the two chief branches of the lateral bundle. The course +of the vessels is very complex at the larger inosculation; and here vessels, +retaining the same diameter, are often formed by the union of the bluntly +pointed ends of two vessels, but whether these points open into each other by +their attached surfaces, I do not know. By means of the two inosculations all +the vessels on the same side of the leaf are brought into some sort of +connection. Near the circumference of the larger leaves the bifurcating +branches also come into close union, and then separate again, forming a +continuous zigzag line of vessels round the whole circumference. But the union +of the vessels in this zigzag line seems to be much less intimate than at the +main inosculation. It should be added that the course of the vessels differs +somewhat in different leaves, and even on opposite sides of the same leaf, but +the main inosculation is always present. +</p> + +<p> +Now in my first experiments with bits of meat placed on one side of the disc, +it so happened that not a single tentacle was inflected on the opposite side; +and when I saw that the vessels on the same side were all connected together by +the two inosculations, whilst not a vessel passed over to the opposite side, it +seemed probable that the motor impulse was conducted exclusively along them. +</p> + +<p> +In order to test this view, I divided transversely with the point of a lancet +the central trunks of four leaves, just beneath the main bifurcation; and two +days afterwards placed rather large bits of raw meat [page 249] (a most +powerful stimulant) near the centre of the disc above the incision—that +is, a little towards the apex—with the following results:— +</p> + +<p> +[(1) This leaf proved rather torpid: after 4 hrs. 40 m. (in all cases reckoning +from the time when the meat was given) the tentacles at the distal end were a +little inflected, but nowhere else; they remained so for three days, and +re-expanded on the fourth day. The leaf was then dissected, and the trunk, as +well as the two sublateral branches, were found divided. +</p> + +<p> +(2) After 4 hrs. 30 m. many of the tentacles at the distal end were well +inflected. Next day the blade and all the tentacles at this end were strongly +inflected, and were separated by a distinct transverse line from the basal half +of the leaf, which was not in the least affected. On the third day, however, +some of the short tentacles on the disc near the base were very slightly +inflected. The incision was found on dissection to extend across the leaf as in +the last case. +</p> + +<p> +(3) After 4 hrs. 30 m. strong inflection of the tentacles at the distal end, +which during the next two days never extended in the least to the basal end. +The incision as before. +</p> + +<p> +(4) This leaf was not observed until 15 hrs. had elapsed, and then all the +tentacles, except the extreme marginal ones, were found equally well inflected +all round the leaf. On careful examination the spiral vessels of the central +trunk were certainly divided; but the incision on one side had not passed +through the fibrous tissue surrounding these vessels, though it had passed +through the tissue on the other side.*] +</p> + +<p> +The appearance presented by the leaves (2) and (3) was very curious, and might +be aptly compared with that of a man with his backbone broken and lower +extremities paralysed. Excepting that the line between the two halves was here +transverse instead of longitudinal, these leaves were in the same state as some +of those in the former experiments, with bits of meat placed on one side of the +disc. The case of leaf (4) +</p> + +<p class="footnote"> +* M. Ziegler made similar experiments by cutting the spiral vessels of Drosera +intermedia(‘Comptes rendus,’ 1874, p. 1417), but arrived at +conclusions widely different from mine. [page 250] +</p> + +<p> +proves that the spiral vessels of the central trunk may be divided, and yet the +motor impulse be transmitted from the distal to the basal end; and this led me +at first to suppose that the motor force was sent through the closely +surrounding fibrous tissue; and that if one half of this tissue was left +undivided, it sufficed for complete transmission. But opposed to this +conclusion is the fact that no vessels pass directly from one side of the leaf +to the other, and yet, as we have seen, if a rather large bit of meat is placed +on one side, the motor impulse is sent, though slowly and imperfectly, in a +transverse direction across the whole breadth of the leaf. Nor can this latter +fact be accounted for by supposing that the transmission is effected through +the two inosculations, or through the circumferential zigzag line of union, for +had this been the case, the exterior tentacles on the opposite side of the disc +would have been affected before the more central ones, which never occurred. We +have also seen that the extreme marginal tentacles appear to have no power to +transmit an impulse to the adjoining tentacles; yet the little bundle of +vessels which enters each marginal tentacle sends off a minute branch to those +on both sides, and this I have not observed in any other tentacles; so that the +marginal ones are more closely connected together by spiral vessels than are +the others, and yet have much less power of communicating a motor impulse to +one another. +</p> + +<p> +But besides these several facts and arguments we have conclusive evidence that +the motor impulse is not sent, at least exclusively, through the spiral +vessels, or through the tissue immediately surrounding them. We know that if a +bit of meat is placed on a gland (the immediately adjoining ones having been +removed) on any part of the disc, all the short sur- [page 251] rounding +tentacles bend almost simultaneously with great precision towards it. Now there +are tentacles on the disc, for instance near the extremities of the sublateral +bundles (fig. 11), which are supplied with vessels that do not come into +contact with the branches that enter the surrounding tentacles, except by a +very long and extremely circuitous course. Nevertheless, if a bit of meat is +placed on the gland of a tentacle of this kind, all the surrounding ones are +inflected towards it with great precision. It is, of course, possible that an +impulse might be sent through a long and circuitous course, but it is obviously +impossible that the direction of the movement could be thus communicated, so +that all the surrounding tentacles should bend precisely to the point of +excitement. The impulse no doubt is transmitted in straight radiating lines +from the excited gland to the surrounding tentacles; it cannot, therefore, be +sent along the fibro-vascular bundles. The effect of cutting the central +vessels, in the above cases, in preventing the transmission of the motor +impulse from the distal to the basal end of a leaf, may be attributed to a +considerable space of the cellular tissue having been divided. We shall +hereafter see, when we treat of Dionaea, that this same conclusion, namely that +the motor impulse is not transmitted by the fibro-vascular bundles, is plainly +confirmed; and Prof. Cohn has come to the same conclusion with respect to +Aldrovanda—both members of the Droseraceae. +</p> + +<p> +As the motor impulse is not transmitted along the vessels, there remains for +its passage only the cellular tissue; and the structure of this tissue explains +to a certain extent how it travels so quickly down the long exterior tentacles, +and much more slowly across the blade of the leaf. We shall also see why it +crosses [page 252] the blade more quickly in a longitudinal than in a +transverse direction; though with time it can pass in any direction. We know +that the same stimulus causes movement of the tentacles and aggregation of the +protoplasm, and that both influences originate in and proceed from the glands +within the same brief space of time. It seems therefore probable that the motor +impulse consists of the first commencement of a molecular change in the +protoplasm, which, when well developed, is plainly visible, and has been +designated aggregation; but to this subject I shall return. We further know +that in the transmission of the aggregating process the chief delay is caused +by the passage of the transverse cell-walls; for as the aggregation travels +down the tentacles, the contents of each successive cell seem almost to flash +into a cloudy mass. We may therefore infer that the motor impulse is in like +manner delayed chiefly by passing through the cell-walls. +</p> + +<p> +The greater celerity with which the impulse is transmitted down the long +exterior tentacles than across the disc may be largely attributed to its being +closely confined within the narrow pedicel, instead of radiating forth on all +sides as on the disc. But besides this confinement, the exterior cells of the +tentacles are fully twice as long as those of the disc; so that only half the +number of transverse partitions have to be traversed in a given length of a +tentacle, compared with an equal space on the disc; and there would be in the +same proportion less retardation of the impulse. Moreover, in sections of the +exterior tentacles given by Dr. Warming,* the parenchymatous +</p> + +<p class="footnote"> +* ‘Videnskabelige Meddelelser de la Soc. d’Hist. nat. de +Copenhague,’ Nos. 10-12, 1872, woodcuts iv. and v. [page 253] +</p> + +<p> +cells are shown to be still more elongated; and these would form the most +direct line of communication from the gland to the bending place of the +tentacle. If the impulse travels down the exterior cells, it would have to +cross from between twenty to thirty transverse partitions; but rather fewer if +down the inner parenchymatous tissue. In either case it is remarkable that the +impulse is able to pass through so many partitions down nearly the whole length +of the pedicel, and to act on the bending place, in ten seconds. Why the +impulse, after having passed so quickly down one of the extreme marginal +tentacles (about 1/20 of an inch in length), should never, as far as I have +seen, affect the adjoining tentacles, I do not understand. It may be in part +accounted for by much energy being expended in the rapidity of the +transmission. +</p> + +<p> +Most of the cells of the disc, both the superficial ones and the larger cells +which form the five or six underlying layers, are about four times as long as +broad. They are arranged almost longitudinally, radiating from the footstalk. +The motor impulse, therefore, when transmitted across the disc, has to cross +nearly four times as many cell-walls as when transmitted in a longitudinal +direction, and would consequently be much delayed in the former case. The cells +of the disc converge towards the bases of the tentacles, and are thus fitted to +convey the motor impulse to them from all sides. On the whole, the arrangement +and shape of the cells, both those of the disc and tentacles, throw much light +on the rate and manner of diffusion of the motor impulse. But why the impulse +proceeding from the glands of the exterior rows of tentacles tends to travel +laterally and towards the centre of the leaf, but not centrifugally, is by no +means clear. [page 254] +</p> + +<p> +Mechanism of the Movements, and Nature of the Motor Impulse.—Whatever may +be the means of movement, the exterior tentacles, considering their delicacy, +are inflected with much force. A bristle, held so that a length of 1 inch +projected from a handle, yielded when I tried to lift with it an inflected +tentacle, which was somewhat thinner than the bristle. The amount or extent, +also, of the movement is great. Fully expanded tentacles in becoming inflected +sweep through an angle of 180o; and if they are beforehand reflexed, as often +occurs, the angle is considerably greater. It is probably the superficial cells +at the bending place which chiefly or exclusively contract; for the interior +cells have very delicate walls, and are so few in number that they could hardly +cause a tentacle to bend with precision to a definite point. Though I carefully +looked, I could never detect any wrinkling of the surface at the bending place, +even in the case of a tentacle abnormally curved into a complete circle, under +circumstances hereafter to be mentioned. +</p> + +<p> +All the cells are not acted on, though the motor impulse passes through them. +When the gland of one of the long exterior tentacles is excited, the upper +cells are not in the least affected; about halfway down there is a slight +bending, but the chief movement is confined to a short space near the base; and +no part of the inner tentacles bends except the basal portion. With respect to +the blade of the leaf, the motor impulse may be transmitted through many cells, +from the centre to the circumference, without their being in the least +affected, or they may be strongly acted on and the blade greatly inflected. In +the latter case the movement seems to depend partly on the strength of the +stimulus, and partly on [page 255] its nature, as when leaves are immersed in +certain fluids. +</p> + +<p> +The power of movement which various plants possess, when irritated, has been +attributed by high authorities to the rapid passage of fluid out of certain +cells, which, from their previous state of tension, immediately contract.* +Whether or not this is the primary cause of such movements, fluid must pass out +of closed cells when they contract or are pressed together in one direction, +unless they at the same time expand in some other direction. For instance, +fluid can be seen to ooze from the surface of any young and vigorous shoot if +slowly bent into a semi-circle.** In the case of Drosera there is certainly +much movement of the fluid throughout the tentacles whilst they are undergoing +inflection. Many leaves can be found in which the purple fluid within the cells +is of an equally dark tint on the upper and lower sides of the tentacles, +extending also downwards on both sides to equally near their bases. If the +tentacles of such a leaf are excited into movement, it will generally be found +after some hours that the cells on the concave side are much paler than they +were before, or are quite colourless, those on the convex side having become +much darker. In two instances, after particles of hair had been placed on +glands, and when in the course of 1 hr. 10 m. the tentacles were incurved +halfway towards the centre of the leaf, this change of colour in the two sides +was conspicuously plain. In another case, after a bit of meat had been placed +on a gland, the purple colour was observed at intervals to be slowly travelling +from the upper to the lower part, down the convex side of +</p> + +<p class="footnote"> +* Sachs, ‘Traité de Bot.’ 3rd edit. 1874, p. 1038. This view was, I +believe, first suggested by Lamarck. +</p> + +<p class="footnote"> +** Sachs, ibid. p. 919. [page 256] +</p> + +<p> +the bending tentacle. But it does not follow from these observations that the +cells on the convex side become filled with more fluid during the act of +inflection than they contained before; for fluid may all the time be passing +into the disc or into the glands which then secrete freely. +</p> + +<p> +The bending of the tentacles, when leaves are immersed in a dense fluid, and +their subsequent re-expansion in a less dense fluid, show that the passage of +fluid from or into the cells can cause movements like the natural ones. But the +inflection thus caused is often irregular; the exterior tentacles being +sometimes spirally curved. Other unnatural movements are likewise caused by the +application of dense fluids, as in the case of drops of syrup placed on the +backs of leaves and tentacles. Such movements may be compared with the +contortions which many vegetable tissues undergo when subjected to exosmose. It +is therefore doubtful whether they throw any light on the natural movements. +</p> + +<p> +If we admit that the outward passage of fluid is the cause of the bending of +the tentacles, we must suppose that the cells, before the act of inflection, +are in a high state of tension, and that they are elastic to an extraordinary +degree; for otherwise their contraction could not cause the tentacles often to +sweep through an angle of above 180o. Prof. Cohn, in his interesting paper* on +the movements of the stamens of certain Compositae, states that these organs, +when dead, are as elastic as threads of india-rubber, and are then only half as +long as they were when alive. He believes that the living protoplasm +</p> + +<p class="footnote"> +* ‘Abhand. der Schles. Gesell. fr vaterl. Cultur,’ 1861, Heft i. An +excellent abstract of this paper is given in the ‘Annals and Mag. of Nat. +Hist.’ 3rd series, 1863, vol. xi. pp. 188-197. [page 257] +</p> + +<p> +within their cells is ordinarily in a state of expansion, but is paralysed by +irritation, or may be said to suffer temporary death; the elasticity of the +cell-walls then coming into play, and causing the contraction of the stamens. +Now the cells on the upper or concave side of the bending part of the tentacles +of Drosera do not appear to be in a state of tension, nor to be highly elastic; +for when a leaf is suddenly killed, or dies slowly, it is not the upper but the +lower sides of the tentacles which contract from elasticity. We may, therefore, +conclude that their movements cannot be accounted for by the inherent +elasticity of certain cells, opposed as long as they are alive and not +irritated by the expanded state of their contents. +</p> + +<p> +A somewhat different view has been advanced by other physiologists—namely +that the protoplasm, when irritated, contracts like the soft sarcode of the +muscles of animals. In Drosera the fluid within the cells of the tentacles at +the bending place appears under the microscope thin and homogeneous, and after +aggregation consists of small, soft masses of matter, undergoing incessant +changes of form and floating in almost colourless fluid. These masses are +completely redissolved when the tentacles re-expand. Now it seems scarcely +possible that such matter should have any direct mechanical power; but if +through some molecular change it were to occupy less space than it did before, +no doubt the cell-walls would close up and contract. But in this case it might +be expected that the walls would exhibit wrinkles, and none could ever be seen. +Moreover, the contents of all the cells seem to be of exactly the same nature, +both before and after aggregation; and yet only a few of the basal cells +contract, the rest of the tentacle remaining straight. +</p> + +<p> +A third view maintained by some physiologists, [page 258] though rejected by +most others, is that the whole cell, including the walls, actively contracts. +If the walls are composed solely of non-nitrogenous cellulose, this view is +highly improbable; but it can hardly be doubted that they must be permeated by +proteid matter, at least whilst they are growing. Nor does there seem any +inherent improbability in the cell-walls of Drosera contracting, considering +their high state of organisation; as shown in the case of the glands by their +power of absorption and secretion, and by being exquisitely sensitive so as to +be affected by the pressure of the most minute particles. The cell-walls of the +pedicels also allow various impulses to pass through them, inducing movement, +increased secretion and aggregation. On the whole the belief that the walls of +certain cells contract, some of their contained fluid being at the same time +forced outwards, perhaps accords best with the observed facts. If this view is +rejected, the next most probable one is that the fluid contents of the cells +shrink, owing to a change in their molecular state, with the consequent closing +in of the walls. Anyhow, the movement can hardly be attributed to the +elasticity of the walls, together with a previous state of tension. +</p> + +<p> +With respect to the nature of the motor impulse which is transmitted from the +glands down the pedicels and across the disc, it seems not improbable that it +is closely allied to that influence which causes the protoplasm within the +cells of the glands and tentacles to aggregate. We have seen that both forces +originate in and proceed from the glands within a few seconds of the same time, +and are excited by the same causes. The aggregation of the protoplasm lasts +almost as long as the tentacles remain inflected, even though this be for more +than a week; but the [page 259] protoplasm is redissolved at the bending place +shortly before the tentacles re-expand, showing that the exciting cause of the +aggregating process has then quite ceased. Exposure to carbonic acid causes +both the latter process and the motor impulse to travel very slowly down the +tentacles. We know that the aggregating process is delayed in passing through +the cell- walls, and we have good reason to believe that this holds good with +the motor impulse; for we can thus understand the different rates of its +transmission in a longitudinal and transverse line across the disc. Under a +high power the first sign of aggregation is the appearance of a cloud, and soon +afterwards of extremely fine granules, in the homogeneous purple fluid within +the cells; and this apparently is due to the union of molecules of protoplasm. +Now it does not seem an improbable view that the same tendency—namely for +the molecules to approach each other—should be communicated to the inner +surfaces of the cell-walls which are in contact with the protoplasm; and if so, +their molecules would approach each other, and the cell-wall would contract. +</p> + +<p> +To this view it may with truth be objected that when leaves are immersed in +various strong solutions, or are subjected to a heat of above 130° Fahr. (54°.4 +Cent.), aggregation ensues, but there is no movement. Again, various acids and +some other fluids cause rapid movement, but no aggregation, or only of an +abnormal nature, or only after a long interval of time; but as most of these +fluids are more or less injurious, they may check or prevent the aggregating +process by injuring or killing the protoplasm. There is another and more +important difference in the two processes: when the glands on the disc are +excited, they transmit some influence up the surrounding [page 260] tentacles, +which acts on the cells at the bending place, but does not induce aggregation +until it has reached the glands; these then send back some other influence, +causing the protoplasm to aggregate, first in the upper and then in the lower +cells. +</p> + +<p> +The Re-expansion of the Tentacles.—This movement is always slow and +gradual. When the centre of the leaf is excited, or a leaf is immersed in a +proper solution, all the tentacles bend directly towards the centre, and +afterwards directly back from it. But when the point of excitement is on one +side of the disc, the surrounding tentacles bend towards it, and therefore +obliquely with respect to their normal direction; when they afterwards +re-expand, they bend obliquely back, so as to recover their original positions. +The tentacles farthest from an excited point, wherever that may be, are the +last and the least affected, and probably in consequence of this they are the +first to re-expand. The bent portion of a closely inflected tentacle is in a +state of active contraction, as shown by the following experiment. Meat was +placed on a leaf, and after the tentacles were closely inflected and had quite +ceased to move, narrow strips of the disc, with a few of the outer tentacles +attached to it, were cut off and laid on one side under the microscope. After +several failures, I succeeded in cutting off the convex surface of the bent +portion of a tentacle. Movement immediately recommenced, and the already +greatly bent portion went on bending until it formed a perfect circle; the +straight distal portion of the tentacle passing on one side of the strip. The +convex surface must therefore have previously been in a state of tension, +sufficient to counter-balance that of the concave surface, which, when free, +curled into a complete ring. +</p> + +<p> +The tentacles of an expanded and unexcited leaf [page 261] are moderately rigid +and elastic; if bent by a needle, the upper end yields more easily than the +basal and thicker part, which alone is capable of becoming inflected. The +rigidity of this basal part seems due to the tension of the outer surface +balancing a state of active and persistent contraction of the cells of the +inner surface. I believe that this is the case, because, when a leaf is dipped +into boiling water, the tentacles suddenly become reflexed, and this apparently +indicates that the tension of the outer surface is mechanical, whilst that of +the inner surface is vital, and is instantly destroyed by the boiling water. We +can thus also understand why the tentacles as they grow old and feeble slowly +become much reflexed. If a leaf with its tentacles closely inflected is dipped +into boiling water, these rise up a little, but by no means fully re-expand. +This may be owing to the heat quickly destroying the tension and elasticity of +the cells of the convex surface; but I can hardly believe that their tension, +at any one time, would suffice to carry back the tentacles to their original +position, often through an angle of above 180o. It is more probable that fluid, +which we know travels along the tentacles during the act of inflection, is +slowly re-attracted into the cells of the convex surface, their tension being +thus gradually and continually increased. +</p> + +<p> +A recapitulation of the chief facts and discussions in this chapter will be +given at the close of the next chapter. [page 262] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0011" id="link2HCH0011"></a> +CHAPTER XI.<br/> +RECAPITULATION OF THE CHIEF OBSERVATIONS ON DROSERA ROTUNDIFOLIA.</h2> + +<p> +As summaries have been given to most of the chapters, it will be sufficient +here to recapitulate, as briefly as I can, the chief points. In the first +chapter a preliminary sketch was given of the structure of the leaves, and of +the manner in which they capture insects. This is effected by drops of +extremely viscid fluid surrounding the glands and by the inward movement of the +tentacles. As the plants gain most of their nutriment by this means, their +roots are very poorly developed; and they often grow in places where hardly any +other plant except mosses can exist. The glands have the power of absorption, +besides that of secretion. They are extremely sensitive to various stimulants, +namely repeated touches, the pressure of minute particles, the absorption of +animal matter and of various fluids, heat, and galvanic action. A tentacle with +a bit of raw meat on the gland has been seen to begin bending in 10 s., to be +strongly incurved in 5 m., and to reach the centre of the leaf in half an hour. +The blade of the leaf often becomes so much inflected that it forms a cup, +enclosing any object placed on it. +</p> + +<p> +A gland, when excited, not only sends some influence down its own tentacle, +causing it to bend, but likewise to the surrounding tentacles, which become +incurved; so that the bending place can be acted on by an impulse received from +opposite directions, [page 263] namely from the gland on the summit of the same +tentacle, and from one or more glands of the neighbouring tentacles. Tentacles, +when inflected, re-expand after a time, and during this process the glands +secrete less copiously, or become dry. As soon as they begin to secrete again, +the tentacles are ready to re-act; and this may be repeated at least three, +probably many more times. +</p> + +<p> +It was shown in the second chapter that animal substances placed on the discs +cause much more prompt and energetic inflection than do inorganic bodies of the +same size, or mere mechanical irritation; but there is a still more marked +difference in the greater length of time during which the tentacles remain +inflected over bodies yielding soluble and nutritious matter, than over those +which do not yield such matter. Extremely minute particles of glass, cinders, +hair, thread, precipitated chalk, &c., when placed on the glands of the +outer tentacles, cause them to bend. A particle, unless it sinks through the +secretion and actually touches the surface of the gland with some one point, +does not produce any effect. A little bit of thin human hair 8/1000 of an inch +(.203 mm.) in length, and weighing only 1/78740 of a grain (.000822 mg.), +though largely supported by the dense secretion, suffices to induce movement. +It is not probable that the pressure in this case could have amounted to that +from the millionth of a grain. Even smaller particles cause a slight movement, +as could be seen through a lens. Larger particles than those of which the +measurements have been given cause no sensation when placed on the tongue, one +of the most sensitive parts of the human body. +</p> + +<p> +Movement ensues if a gland is momentarily touched three or four times; but if +touched only once or twice, [page 264] though with considerable force and with +a hard object, the tentacle does not bend. The plant is thus saved from much +useless movement, as during a high wind the glands can hardly escape being +occasionally brushed by the leaves of surrounding plants. Though insensible to +a single touch, they are exquisitely sensitive, as just stated, to the +slightest pressure if prolonged for a few seconds; and this capacity is +manifestly of service to the plant in capturing small insects. Even gnats, if +they rest on the glands with their delicate feet, are quickly and securely +embraced. The glands are insensible to the weight and repeated blows of drops +of heavy rain, and the plants are thus likewise saved from much useless +movement. +</p> + +<p> +The description of the movements of the tentacles was interrupted in the third +chapter for the sake of describing the process of aggregation. This process +always commences in the cells of the glands, the contents of which first become +cloudy; and this has been observed within 10 s. after a gland has been excited. +Granules just resolvable under a very high power soon appear, sometimes within +a minute, in the cells beneath the glands; and these then aggregate into minute +spheres. The process afterwards travels down the tentacles, being arrested for +a short time at each transverse partition. The small spheres coalesce into +larger spheres, or into oval, club-headed, thread- or necklace-like, or +otherwise shaped masses of protoplasm, which, suspended in almost colourless +fluid, exhibit incessant spontaneous changes of form. These frequently coalesce +and again separate. If a gland has been powerfully excited, all the cells down +to the base of the tentacle are affected. In cells, especially if filled with +dark red fluid, the first step in the [page 265] process often is the formation +of a dark red, bag-like mass of protoplasm, which afterwards divides and +undergoes the usual repeated changes of form. Before any aggregation has been +excited, a sheet of colourless protoplasm, including granules (the primordial +utricle of Mohl), flows round the walls of the cells; and this becomes more +distinct after the contents have been partially aggregated into spheres or +bag-like masses. But after a time the granules are drawn towards the central +masses and unite with them; and then the circulating sheet can no longer be +distinguished, but there is still a current of transparent fluid within the +cells. +</p> + +<p> +Aggregation is excited by almost all the stimulants which induce movement; such +as the glands being touched two or three times, the pressure of minute +inorganic particles, the absorption of various fluids, even long immersion in +distilled water, exosmose, and heat. Of the many stimulants tried, carbonate of +ammonia is the most energetic and acts the quickest: a dose of 1/134400 of a +grain (.00048 mg.) given to a single gland suffices to cause in one hour +well-marked aggregation in the upper cells of the tentacle. The process goes on +only as long as the protoplasm is in a living, vigorous, and oxygenated +condition. +</p> + +<p> +The result is in all respects exactly the same, whether a gland has been +excited directly, or has received an influence from other and distant glands. +But there is one important difference: when the central glands are irritated, +they transmit centrifugally an influence up the pedicels of the exterior +tentacles to their glands; but the actual process of aggregation travels +centripetally, from the glands of the exterior tentacles down their pedicels. +The exciting influence, therefore, which is transmitted from [page 266] one +part of the leaf to another must be different from that which actually induces +aggregation. The process does not depend on the glands secreting more copiously +than they did before; and is independent of the inflection of the tentacles. It +continues as long as the tentacles remain inflected, and as soon as these are +fully re-expanded, the little masses of protoplasm are all redissolved; the +cells becoming filled with homogeneous purple fluid, as they were before the +leaf was excited. +</p> + +<p> +As the process of aggregation can be excited by a few touches, or by the +pressure of insoluble particles, it is evidently independent of the absorption +of any matter, and must be of a molecular nature. Even when caused by the +absorption of the carbonate or other salt of ammonia, or an infusion of meat, +the process seems to be of exactly the same nature. The protoplasmic fluid +must, therefore, be in a singularly unstable condition, to be acted on by such +slight and varied causes. Physiologists believe that when a nerve is touched, +and it transmits an influence to other parts of the nervous system, a molecular +change is induced in it, though not visible to us. Therefore it is a very +interesting spectacle to watch the effects on the cells of a gland, of the +pressure of a bit of hair, weighing only 1/78700 of a grain and largely +supported by the dense secretion, for this excessively slight pressure soon +causes a visible change in the protoplasm, which change is transmitted down the +whole length of the tentacle, giving it at last a mottled appearance, +distinguishable even by the naked eye. +</p> + +<p> +In the fourth chapter it was shown that leaves placed for a short time in water +at a temperature of 110° Fahr. (43°.3 Cent.) become somewhat inflected; they +are thus also rendered more sensitive to the action [page 267] of meat than +they were before. If exposed to a temperature of between 115° and +125°(46°.1-51°.6 Cent.), they are quickly inflected, and their protoplasm +undergoes aggregation; when afterwards placed in cold water, they re-expand. +Exposed to 130° (54°.4 Cent.), no inflection immediately occurs, but the leaves +are only temporarily paralysed, for on being left in cold water, they often +become inflected and afterwards re-expand. In one leaf thus treated, I +distinctly saw the protoplasm in movement. In other leaves, treated in the same +manner, and then immersed in a solution of carbonate of ammonia, strong +aggregation ensued. Leaves placed in cold water, after an exposure to so high a +temperature as 145° (62°.7 Cent.), sometimes become slightly, though slowly, +inflected; and afterwards have the contents of their cells strongly aggregated +by carbonate of ammonia. But the duration of the immersion is an important +element, for if left in water at 145° (62°.7 Cent.), or only at 140° (60° +Cent.), until it becomes cool, they are killed, and the contents of the glands +are rendered white and opaque. This latter result seems to be due to the +coagulation of the albumen, and was almost always caused by even a short +exposure to 150° (65.5 Cent.); but different leaves, and even the separate +cells in the same tentacle, differ considerably in their power of resisting +heat. Unless the heat has been sufficient to coagulate the albumen, carbonate +of ammonia subsequently induces aggregation. +</p> + +<p> +In the fifth chapter, the results of placing drops of various nitrogenous and +non-nitrogenous organic fluids on the discs of leaves were given, and it was +shown that they detect with almost unerring certainty the presence of nitrogen. +A decoction of green peas or of fresh cabbage-leaves acts almost as powerfully +as an infusion of raw meat; whereas an infusion of cabbage- [page 268] leaves +made by keeping them for a long time in merely warm water is far less +efficient. A decoction of grass-leaves is less powerful than one of green peas +or cabbage-leaves. +</p> + +<p> +These results led me to inquire whether Drosera possessed the power of +dissolving solid animal matter. The experiments proving that the leaves are +capable of true digestion, and that the glands absorb the digested matter, are +given in detail in the sixth chapter. These are, perhaps, the most interesting +of all my observations on Drosera, as no such power was before distinctly known +to exist in the vegetable kingdom. It is likewise an interesting fact that the +glands of the disc, when irritated, should transmit some influence to the +glands of the exterior tentacles, causing them to secrete more copiously and +the secretion to become acid, as if they had been directly excited by an object +placed on them. The gastric juice of animals contains, as is well known, an +acid and a ferment, both of which are indispensable for digestion, and so it is +with the secretion of Drosera. When the stomach of an animal is mechanically +irritated, it secretes an acid, and when particles of glass or other such +objects were placed on the glands of Drosera, the secretion, and that of the +surrounding and untouched glands, was increased in quantity and became acid. +But, according to Schiff, the stomach of an animal does not secrete its proper +ferment, pepsin, until certain substances, which he calls peptogenes, are +absorbed; and it appears from my experiments that some matter must be absorbed +by the glands of Drosera before they secrete their proper ferment. That the +secretion does contain a ferment which acts only in the presence of an acid on +solid animal matter, was clearly proved by adding minute doses of [page 269] an +alkali, which entirely arrested the process of digestion, this immediately +recommencing as soon as the alkali was neutralised by a little weak +hydrochloric acid. From trials made with a large number of substances, it was +found that those which the secretion of Drosera dissolves completely, or +partially, or not at all, are acted on in exactly the same manner by gastric +juice. We may, therefore, conclude that the ferment of Drosera is closely +analogous to, or identical with, the pepsin of animals. +</p> + +<p> +The substances which are digested by Drosera act on the leaves very +differently. Some cause much more energetic and rapid inflection of the +tentacles, and keep them inflected for a much longer time, than do others. We +are thus led to believe that the former are more nutritious than the latter, as +is known to be the case with some of these same substances when given to +animals; for instance, meat in comparison with gelatine. As cartilage is so +tough a substance and is so little acted on by water, its prompt dissolution by +the secretion of Drosera, and subsequent absorption is, perhaps, one of the +most striking cases. But it is not really more remarkable than the digestion of +meat, which is dissolved by this secretion in the same manner and by the same +stages as by gastric juice. The secretion dissolves bone, and even the enamel +of teeth, but this is simply due to the large quantity of acid secreted, owing, +apparently, to the desire of the plant for phosphorus. In the case of bone, the +ferment does not come into play until all the phosphate of lime has been +decomposed and free acid is present, and then the fibrous basis is quickly +dissolved. Lastly, the secretion attacks and dissolves matter out of living +seeds, which it sometimes kills, or injures, as shown by the diseased state +[page 270] of the seedlings. It also absorbs matter from pollen, and from +fragments of leaves. +</p> + +<p> +The seventh chapter was devoted to the action of the salts of ammonia. These +all cause the tentacles, and often the blade of the leaf, to be inflected, and +the protoplasm to be aggregated. They act with very different power; the +citrate being the least powerful, and the phosphate, owing, no doubt, to the +presence of phosphorus and nitrogen, by far the most powerful. But the relative +efficiency of only three salts of ammonia was carefully determined, namely the +carbonate, nitrate, and phosphate. The experiments were made by placing +half-minims (.0296 ml.) of solutions of different strengths on the discs of the +leaves,—by applying a minute drop (about the 1/20 of a minim, or .00296 +ml.) for a few seconds to three or four glands,—and by the immersion of +whole leaves in a measured quantity. In relation to these experiments it was +necessary first to ascertain the effects of distilled water, and it was found, +as described in detail, that the more sensitive leaves are affected by it, but +only in a slight degree. +</p> + +<p> +A solution of the carbonate is absorbed by the roots and induces aggregation in +their cells, but does not affect the leaves. The vapour is absorbed by the +glands, and causes inflection as well as aggregation. A drop of a solution +containing 1/960 of a grain (.0675 mg.) is the least quantity which, when +placed on the glands of the disc, excites the exterior tentacles to bend +inwards. But a minute drop, containing 1/14400 of a grain (.00445 mg.), if +applied for a few seconds to the secretion surrounding a gland, causes the +inflection of the same tentacle. When a highly sensitive leaf is immersed in a +solution, and there is ample time for absorption, the 1/268800 of a grain [page +271] (.00024 mg.) is sufficient to excite a single tentacle into movement. +</p> + +<p> +The nitrate of ammonia induces aggregation of the protoplasm much less quickly +than the carbonate, but is more potent in causing inflection. A drop containing +1/2400 of a grain (.027 mg.) placed on the disc acts powerfully on all the +exterior tentacles, which have not themselves received any of the solution; +whereas a drop with 1/2800 of a grain caused only a few of these tentacles to +bend, but affected rather more plainly the blade. A minute drop applied as +before, and containing 1/28800 of a grain (.0025 mg.), caused the tentacle +bearing this gland to bend. By the immersion of whole leaves, it was proved +that the absorption by a single gland of 1/691200 of a grain (.0000937 mg.) was +sufficient to set the same tentacle into movement. +</p> + +<p> +The phosphate of ammonia is much more powerful than the nitrate. A drop +containing 1/3840 of a grain (.0169 mg.) placed on the disc of a sensitive leaf +causes most of the exterior tentacles to be inflected, as well as the blade of +the leaf. A minute drop containing 1/153600 of a grain (.000423 mg.), applied +for a few seconds to a gland, acts, as shown by the movement of the tentacle. +When a leaf is immersed in thirty minims (1.7748 ml.) of a solution of one part +by weight of the salt to 21,875,000 of water, the absorption by a gland of only +the 1/19760000 of a grain (.00000328 mg.), that is, about the +one-twenty-millionth of a grain, is sufficient to cause the tentacle bearing +this gland to bend to the centre of the leaf. In this experiment, owing to the +presence of the water of crystallisation, less than the one-thirty-millionth of +a grain of the efficient elements could have been absorbed. There is nothing +remarkable in such minute quantities being absorbed by the glands, [page 272] +for all physiologists admit that the salts of ammonia, which must be brought in +still smaller quantity by a single shower of rain to the roots, are absorbed by +them. Nor is it surprising that Drosera should be enabled to profit by the +absorption of these salts, for yeast and other low fungoid forms flourish in +solutions of ammonia, if the other necessary elements are present. But it is an +astonishing fact, on which I will not here again enlarge, that so inconceivably +minute a quantity as the one-twenty-millionth of a grain of phosphate of +ammonia should induce some change in a gland of Drosera, sufficient to cause a +motor impulse to be sent down the whole length of the tentacle; this impulse +exciting movement often through an angle of above 180o. I know not whether to +be most astonished at this fact, or that the pressure of a minute bit of hair, +supported by the dense secretion, should quickly cause conspicuous movement. +Moreover, this extreme sensitiveness, exceeding that of the most delicate part +of the human body, as well as the power of transmitting various impulses from +one part of the leaf to another, have been acquired without the intervention of +any nervous system. +</p> + +<p> +As few plants are at present known to possess glands specially adapted for +absorption, it seemed worth while to try the effects on Drosera of various +other salts, besides those of ammonia, and of various acids. Their action, as +described in the eighth chapter, does not correspond at all strictly with their +chemical affinities, as inferred from the classification commonly followed. The +nature of the base is far more influential than that of the acid; and this is +known to hold good with animals. For instance, nine salts of sodium all caused +well-marked inflection, and none of them were poisonous in small doses; whereas +seven of the nine corre- [page 273] sponding salts of potassium produced no +effect, two causing slight inflection. Small doses, moreover, of some of the +latter salts were poisonous. The salts of sodium and potassium, when injected +into the veins of animals, likewise differ widely in their action. The +so-called earthy salts produce hardly any effect on Drosera. On the other hand, +most of the metallic salts cause rapid and strong inflection, and are highly +poisonous; but there are some odd exceptions to this rule; thus chloride of +lead and zinc, as well as two salts of barium, did not cause inflection, and +were not poisonous. +</p> + +<p> +Most of the acids which were tried, though much diluted (one part to 437 of +water), and given in small doses, acted powerfully on Drosera; nineteen, out of +the twenty-four, causing the tentacles to be more or less inflected. Most of +them, even the organic acids, are poisonous, often highly so; and this is +remarkable, as the juices of so many plants contain acids. Benzoic acid, which +is innocuous to animals, seems to be as poisonous to Drosera as hydrocyanic. On +the other hand, hydrochloric acid is not poisonous either to animals or to +Drosera, and induces only a moderate amount of inflection. Many acids excite +the glands to secrete an extraordinary quantity of mucus; and the protoplasm +within their cells seems to be often killed, as may be inferred from the +surrounding fluid soon becoming pink. It is strange that allied acids act very +differently: formic acid induces very slight inflection, and is not poisonous; +whereas acetic acid of the same strength acts most powerfully and is poisonous. +Lactic acid is also poisonous, but causes inflection only after a considerable +lapse of time. Malic acid acts slightly, whereas citric and tartaric acids +produce no effect. [page 274] +</p> + +<p> +In the ninth chapter the effects of the absorption of various alkaloids and +certain other substances were described. Although some of these are poisonous, +yet as several, which act powerfully on the nervous system of animals, produce +no effect on Drosera, we may infer that the extreme sensibility of the glands, +and their power of transmitting an influence to other parts of the leaf, +causing movement, or modified secretion, or aggregation, does not depend on the +presence of a diffused element, allied to nerve-tissue. One of the most +remarkable facts is that long immersion in the poison of the cobra-snake does +not in the least check, but rather stimulates, the spontaneous movements of the +protoplasm in the cells of the tentacles. Solutions of various salts and acids +behave very differently in delaying or in quite arresting the subsequent action +of a solution of phosphate of ammonia. Camphor dissolved in water acts as a +stimulant, as do small doses of certain essential oils, for they cause rapid +and strong inflection. Alcohol is not a stimulant. The vapours of camphor, +alcohol, chloroform, sulphuric and nitric ether, are poisonous in moderately +large doses, but in small doses serve as narcotics or, anaesthetics, greatly +delaying the subsequent action of meat. But some of these vapours also act as +stimulants, exciting rapid, almost spasmodic movements in the tentacles. +Carbonic acid is likewise a narcotic, and retards the aggregation of the +protoplasm when carbonate of ammonia is subsequently given. The first access of +air to plants which have been immersed in this gas sometimes acts as a +stimulant and induces movement. But, as before remarked, a special +pharmacopoeia would be necessary to describe the diversified effects of various +substances on the leaves of Drosera. +</p> + +<p> +In the tenth chapter it was shown that the sensitive- [page 275] ness of the +leaves appears to be wholly confined to the glands and to the immediately +underlying cells. It was further shown that the motor impulse and other forces +or influences, proceeding from the glands when excited, pass through the +cellular tissue, and not along the fibro-vascular bundles. A gland sends its +motor impulse with great rapidity down the pedicel of the same tentacle to the +basal part which alone bends. The impulse, then passing onwards, spreads on all +sides to the surrounding tentacles, first affecting those which stand nearest +and then those farther off. But by being thus spread out, and from the cells of +the disc not being so much elongated as those of the tentacles, it loses force, +and here travels much more slowly than down the pedicels. Owing also to the +direction and form of the cells, it passes with greater ease and celerity in a +longitudinal than in a transverse line across the disc. The impulse proceeding +from the glands of the extreme marginal tentacles does not seem to have force +enough to affect the adjoining tentacles; and this may be in part due to their +length. The impulse from the glands of the next few inner rows spreads chiefly +to the tentacles on each side and towards the centre of the leaf; but that +proceeding from the glands of the shorter tentacles on the disc radiates almost +equally on all sides. +</p> + +<p> +When a gland is strongly excited by the quantity or quality of the substance +placed on it, the motor impulse travels farther than from one slightly excited; +and if several glands are simultaneously excited, the impulses from all unite +and spread still farther. As soon as a gland is excited, it discharges an +impulse which extends to a considerable distance; but afterwards, whilst the +gland is secreting and absorbing, the impulse suffices only to keep the same +tentacle [page 276] inflected; though the inflection may last for many days. +</p> + +<p> +If the bending place of a tentacle receives an impulse from its own gland, the +movement is always towards the centre of the leaf; and so it is with all the +tentacles, when their glands are excited by immersion in a proper fluid. The +short ones in the middle part of the disc must be excepted, as these do not +bend at all when thus excited. On the other hand, when the motor impulse comes +from one side of the disc, the surrounding tentacles, including the short ones +in the middle of the disc, all bend with precision towards the point of +excitement, wherever this may be seated. This is in every way a remarkable +phenomenon; for the leaf falsely appears as if endowed with the senses of an +animal. It is all the more remarkable, as when the motor impulse strikes the +base of a tentacle obliquely with respect to its flattened surface, the +contraction of the cells must be confined to one, two, or a very few rows at +one end. And different sides of the surrounding tentacles must be acted on, in +order that all should bend with precision to the point of excitement. +</p> + +<p> +The motor impulse, as it spreads from one or more glands across the disc, +enters the bases of the surrounding tentacles, and immediately acts on the +bending place. It does not in the first place proceed up the tentacles to the +glands, exciting them to reflect back an impulse to their bases. Nevertheless, +some influence is sent up to the glands, as their secretion is soon increased +and rendered acid; and then the glands, being thus excited, send back some +other influence (not dependent on increased secretion, nor on the inflection of +the tentacles), causing the protoplasm to aggregate in cell beneath cell. This +may [page 277] be called a reflex action, though probably very different from +that proceeding from the nerve-ganglion of an animal; and it is the only known +case of reflex action in the vegetable kingdom. +</p> + +<p> +About the mechanism of the movements and the nature of the motor impulse we +know very little. During the act of inflection fluid certainly travels from one +part to another of the tentacles. But the hypothesis which agrees best with the +observed facts is that the motor impulse is allied in nature to the aggregating +process; and that this causes the molecules of the cell-walls to approach each +other, in the same manner as do the molecules of the protoplasm within the +cells; so that the cell-walls contract. But some strong objections may be urged +against this view. The re-expansion of the tentacles is largely due to the +elasticity of their outer cells, which comes into play as soon as those on the +inner side cease contracting with prepotent force; but we have reason to +suspect that fluid is continually and slowly attracted into the outer cells +during the act of re-expansion, thus increasing their tension. +</p> + +<p> +I have now given a brief recapitulation of the chief points observed by me, +with respect to the structure, movements, constitution, and habits of Drosera +rotundifolia; and we see how little has been made out in comparison with what +remains unexplained and unknown. [page 278] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0012" id="link2HCH0012"></a> +CHAPTER XII.<br/> +ON THE STRUCTURE AND MOVEMENTS OF SOME OTHER SPECIES OF DROSERA.</h2> + +<p class="letter"> +Drosera anglica—Drosera intermedia—Drosera capensis—Drosera +spathulata—Drosera filiformis—Drosera binata—Concluding +remarks. +</p> + +<p> +I examined six other species of Drosera, some of them inhabitants of distant +countries, chiefly for the sake of ascertaining whether they caught insects. +This seemed the more necessary as the leaves of some of the species differ to +an extraordinary degree in shape from the rounded ones of Drosera rotundifolia. +In functional powers, however, they differ very little. +</p> + +<p> +[Drosera anglica (Hudson).*—The leaves of this species, which was sent to +me from Ireland, are much elongated, and gradually widen from the footstalk to +the bluntly pointed apex. They stand almost erect, and their blades sometimes +exceed 1 inch in length, whilst their breadth is only the 1/5 of an inch. The +glands of all the tentacles have the same structure, so that the extreme +marginal ones do not differ from the others, as in the case of Drosera +rotundifolia. When they are irritated by being roughly touched, or by the +pressure of minute inorganic particles, or by contact with animal matter, or by +the absorption of carbonate of ammonia, the tentacles become inflected; the +basal portion being the chief seat of movement. Cutting or pricking the blade +of the leaf did not excite any movement. They frequently capture insects, and +the glands of the inflected tentacles pour forth much acid secretion. Bits of +roast meat were placed on some glands, and the tentacles began to move in 1 m. +or +</p> + +<p class="footnote"> +* Mrs. Treat has given an excellent account in ‘The American +Naturalist,’ December 1873, p. 705, of Drosera longifolia (which is a +synonym in part of Drosera anglica), of Drosera rotundifolia and filiformis. +[page 279] +</p> + +<p> +1 m. 30 s.; and in 1 hr. 10 m. reached the centre. Two bits of boiled cork, one +of boiled thread, and two of coal-cinders taken from the fire, were placed, by +the aid of an instrument which had been immersed in boiling water, on five +glands; these superfluous precautions having been taken on account of M. +Ziegler’s statements. One of the particles of cinder caused some +inflection in 8 hrs. 45 m., as did after 23 hrs. the other particle of cinder, +the bit of thread, and both bits of cork. Three glands were touched half a +dozen times with a needle; one of the tentacles became well inflected in 17 m., +and re-expanded after 24 hrs.; the two others never moved. The homogeneous +fluid within the cells of the tentacles undergoes aggregation after these have +become inflected; especially if given a solution of carbonate of ammonia; and I +observed the usual movements in the masses of protoplasm. In one case, +aggregation ensued in 1 hr. 10 m. after a tentacle had carried a bit of meat to +the centre. From these facts it is clear that the tentacles of Drosera anglica +behave like those of Drosera rotundifolia. +</p> + +<p> +If an insect is placed on the central glands, or has been naturally caught +there, the apex of the leaf curls inwards. For instance, dead flies were placed +on three leaves near their bases, and after 24 hrs. the previously straight +apices were curled completely over, so as to embrace and conceal the flies; +they had therefore moved through an angle of 180o. After three days the apex of +one leaf, together with the tentacles, began to re-expand. But as far as I have +seen— and I made many trials—the sides of the leaf are never +inflected, and this is the one functional difference between this species and +Drosera rotundifolia. +</p> + +<p> +Drosera intermedia (Hayne).—This species is quite as common in some parts +of England as Drosera rotundifolia. It differs from Drosera anglica, as far as +the leaves are concerned, only in their smaller size, and in their tips being +generally a little reflexed. They capture a large number of insects. The +tentacles are excited into movement by all the causes above specified; and +aggregation ensues, with movement of the protoplasmic masses. I have seen, +through a lens, a tentacle beginning to bend in less than a minute after a +particle of raw meat had been placed on the gland. The apex of the leaf curls +over an exciting object as in the case of Drosera anglica. Acid secretion is +copiously poured over captured insects. A leaf which had embraced a fly with +all its tentacles re-expanded after nearly three days. +</p> + +<p> +Drosera capensis.—This species, a native of the Cape of Good Hope, was +sent to me by Dr. Hooker. The leaves are elongated, slightly concave along the +middle and taper towards the apex, [page 280] which is bluntly pointed and +reflexed. They rise from an almost woody axis, and their greatest peculiarity +consists in their foliaceous green footstalks, which are almost as broad and +even longer than the gland-bearing blade. This species, therefore, probably +draws more nourishment from the air, and less from captured insects, than the +other species of the genus. Nevertheless, the tentacles are crowded together on +the disc, and are extremely numerous; those on the margins being much longer +than the central ones. All the glands have the same form; their secretion is +extremely viscid and acid. +</p> + +<p> +The specimen which I examined had only just recovered from a weak state of +health. This may account for the tentacles moving very slowly when particles of +meat were placed on the glands, and perhaps for my never succeeding in causing +any movement by repeatedly touching them with a needle. But with all the +species of the genus this latter stimulus is the least effective of any. +Particles of glass, cork, and coal-cinders, were placed on the glands of six +tentacles; and one alone moved after an interval of 2 hrs. 30 m. Nevertheless, +two glands were extremely sensitive to very small doses of the nitrate of +ammonia, namely to about 1/20 of a minim of a solution (one part to 5250 of +water), containing only 1/115200 of a grain (.000562 mg.) of the salt. +Fragments of flies were placed on two leaves near their tips, which became +incurved in 15 hrs. A fly was also placed in the middle of the leaf; in a few +hours the tentacles on each side embraced it, and in 8 hrs. the whole leaf +directly beneath the fly was a little bent transversely. By the next morning, +after 23 hrs., the leaf was curled so completely over that the apex rested on +the upper end of the footstalk. In no case did the sides of the leaves become +inflected. A crushed fly was placed on the foliaceous footstalk, but produced +no effect. +</p> + +<p> +Drosera spathulata (sent to me by Dr. Hooker).—I made only a few +observations on this Australian species, which has long, narrow leaves, +gradually widening towards their tips. The glands of the extreme marginal +tentacles are elongated and differ from the others, as in the case of Drosera +rotundifolia. A fly was placed on a leaf, and in 18 hrs. it was embraced by the +adjoining tentacles. Gum-water dropped on several leaves produced no effect. A +fragment of a leaf was immersed in a few drops of a solution of one part of +carbonate of ammonia to 146 of water; all the glands were instantly blackened; +the process of aggregation could be seen travelling rapidly down the cells of +the tentacles; and the granules of protoplasm soon united into spheres and +variously shaped masses, which displayed the usual move- [page 281] ments. Half +a minim of a solution of one part of nitrate of ammonia to 146 of water was +next placed on the centre of a leaf; after 6 hrs. some marginal tentacles on +both sides were inflected, and after 9 hrs. they met in the centre. The lateral +edges of the leaf also became incurved, so that it formed a half-cylinder; but +the apex of the leaf in none of my few trials was inflected. The above dose of +the nitrate (viz. 1/320 of a grain, or .202 mg.) was too powerful, for in the +course of 23 hrs. the leaf died. +</p> + +<p> +Drosera filiformis.—This North American species grows in such abundance +in parts of New Jersey as almost to cover the ground. It catches, according to +Mrs. Treat,* an extraordinary number of small and large insects, even great +flies of the genus Asilus, moths, and butterflies. The specimen which I +examined, sent me by Dr. Hooker, had thread-like leaves, from 6 to 12 inches in +length, with the upper surface convex and the lower flat and slightly +channelled. The whole convex surface, down to the roots—for there is no +distinct footstalk—is covered with short gland-bearing tentacles, those +on the margins being the longest and reflexed. Bits of meat placed on the +glands of some tentacles caused them to be slightly inflected in 20 m.; but the +plant was not in a vigorous state. After 6 hrs. they moved through an angle of +90o, and in 24 hrs. reached the centre. The surrounding tentacles by this time +began to curve inwards. Ultimately a large drop of extremely viscid, slightly +acid secretion was poured over the meat from the united glands. Several other +glands were touched with a little saliva, and the tentacles became incurved in +under 1 hr., and re-expanded after 18 hrs. Particles of glass, cork, cinders, +thread, and gold-leaf, were placed on numerous glands on two leaves; in about 1 +hr. four tentacles became curved, and four others after an additional interval +of 2 hrs. 30 m. I never once succeeded in causing any movement by repeatedly +touching the glands with a needle; and Mrs. Treat made similar trials for me +with no success. Small flies were placed on several leaves near their tips, but +the thread-like blade became only on one occasion very slightly bent, directly +beneath the insect. Perhaps this indicates that the blades of vigorous plants +would bend over captured insects, and Dr. Canby informs me that this is the +case; but the movement cannot be strongly pronounced, as it was not observed by +Mrs. Treat. +</p> + +<p> +Drosera binata (or dichotoma).—I am much indebted to Lady +</p> + +<p class="footnote"> +* ‘American Naturalist,’ December 1873, page 705. [page 282] +</p> + +<p> +Dorothy Nevill for a fine plant of this almost gigantic Australian species, +which differs in some interesting points from those previously described. In +this specimen the rush-like footstalks of the leaves were 20 inches in length. +The blade bifurcates at its junction with the footstalk, and twice or thrice +afterwards, curling about in an irregular manner. It is narrow, being only 3/20 +of an inch in breadth. One blade was 7 1/2 inches long, so that the entire +leaf, including the footstalk, was above 27 inches in length. Both surfaces are +slightly hollowed out. The upper surface is covered with tentacles arranged in +alternate rows; those in the middle being short and crowded together, those +towards the margins longer, even twice or thrice as long as the blade is broad. +The glands of the exterior tentacles are of a much darker red than those of the +central ones. The pedicels of all are green. The apex of the blade is +attenuated, and bears very long tentacles. Mr. Copland informs me that the +leaves of a plant which he kept for some years were generally covered with +captured insects before they withered. +</p> + +<p> +The leaves do not differ in essential points of structure or of function from +those of the previously described species. Bits of meat or a little saliva +placed on the glands of the exterior tentacles caused well-marked movement in 3 +m., and particles of glass acted in 4 m. The tentacles with the latter +particles re-expanded after 22 hrs. A piece of leaf immersed in a few drops of +a solution of one part of carbonate of ammonia to 437 of water had all the +glands blackened and all the tentacles inflected in 5 m. A bit of raw meat, +placed on several glands in the medial furrow, was well clasped in 2 hrs. 10 m. +by the marginal tentacles on both sides. Bits of roast meat and small flies did +not act quite so quickly; and albumen and fibrin still less quickly. One of the +bits of meat excited so much secretion (which is always acid) that it flowed +some way down the medial furrow, causing the inflection of the tentacles on +both sides as far as it extended. Particles of glass placed on the glands in +the medial furrow did not stimulate them sufficiently for any motor impulse to +be sent to the outer tentacles. In no case was the blade of the leaf, even the +attenuated apex, at all inflected. +</p> + +<p> +On both the upper and lower surface of the blade there are numerous minute, +almost sessile glands, consisting of four, eight, or twelve cells. On the lower +surface they are pale purple, on the upper greenish. Nearly similar organs +occur on the foot-stalks, but they are smaller and often in a shrivelled +condition. The minute glands on the blade can absorb rapidly: thus, a piece of +leaf was immersed in a solution of one part of carbonate [page 283] of ammonia +to 218 of water (1 gr. to 2 oz.), and in 5 m. they were all so much darkened as +to be almost black, with their contents aggregated. They do not, as far as I +could observe, secrete spontaneously; but in between 2 and 3 hrs. after a leaf +had been rubbed with a bit of raw meat moistened with saliva, they seemed to be +secreting freely; and this conclusion was afterwards supported by other +appearances. They are, therefore, homologous with the sessile glands hereafter +to be described on the leaves of Dionaea and Drosophyllum. In this latter genus +they are associated, as in the present case, with glands which secrete +spontaneously, that is, without being excited. +</p> + +<p> +Drosera binata presents another and more remarkable peculiarity, namely, the +presence of a few tentacles on the backs of the leaves, near their margins. +These are perfect in structure; spiral vessels run up their pedicels; their +glands are surrounded by drops of viscid secretion, and they have the power of +absorbing. This latter fact was shown by the glands immediately becoming black, +and the protoplasm aggregated, when a leaf was placed in a little solution of +one part of carbonate of ammonia to 437 of water. These dorsal tentacles are +short, not being nearly so long as the marginal ones on the upper surface; some +of them are so short as almost to graduate into the minute sessile glands. +Their presence, number, and size, vary on different leaves, and they are +arranged rather irregularly. On the back of one leaf I counted as many as +twenty-one along one side. +</p> + +<p> +These dorsal tentacles differ in one important respect from those on the upper +surface, namely, in not possessing any power of movement, in whatever manner +they may be stimulated. Thus, portions of four leaves were placed at different +times in solutions of carbonate of ammonia (one part to 437 or 218 of water), +and all the tentacles on the upper surface soon became closely inflected; but +the dorsal ones did not move, though the leaves were left in the solution for +many hours, and though their glands from their blackened colour had obviously +absorbed some of the salt. Rather young leaves should be selected for such +trials, for the dorsal tentacles, as they grow old and begin to wither, often +spontaneously incline towards the middle of the leaf. If these tentacles had +possessed the power of movement, they would not have been thus rendered more +serviceable to the plant; for they are not long enough to bend round the margin +of the leaf so as to reach an insect caught on the upper surface, Nor would it +have been of any use if these tentacles could have [page 284] moved towards the +middle of the lower surface, for there are no viscid glands there by which +insects can be caught. Although they have no power of movement, they are +probably of some use by absorbing animal matter from any minute insect which +may be caught by them, and by absorbing ammonia from the rain-water. But their +varying presence and size, and their irregular position, indicate that they are +not of much service, and that they are tending towards abortion. In a future +chapter we shall see that Drosophyllum, with its elongated leaves, probably +represents the condition of an early progenitor of the genus Drosera; and none +of the tentacles of Drosophyllum, neither those on the upper nor lower surface +of the leaves, are capable of movement when excited, though they capture +numerous insects, which serve as nutriment. Therefore it seems that Drosera +binata has retained remnants of certain ancestral characters—namely a few +motionless tentacles on the backs of the leaves, and fairly well developed +sessile glands—which have been lost by most or all of the other species +of the genus.] +</p> + +<p> +Concluding Remarks.—From what we have now seen, there can be little doubt +that most or probably all the species of Drosera are adapted for catching +insects by nearly the same means. Besides the two Australian species above +described, it is said* that two other species from this country, namely Drosera +pallida and Drosera sulphurea, “close their leaves upon insects with +great rapidity: and the same phenomenon is manifested by an Indian species, D. +lunata, and by several of those of the Cape of Good Hope, especially by D. +trinervis.” Another Australian species, Drosera heterophylla (made by +Lindley into a distinct genus, Sondera) is remarkable from its peculiarly +shaped leaves, but I know nothing of its power of catching insects, for I have +seen only dried specimens. The leaves form minute flattened cups, with the +footstalks attached not to one margin, but to the bottom. The +</p> + +<p class="footnote"> +* ‘Gardener’s Chronicle,’ 1874, p. 209. [page 285] +</p> + +<p> +inner surface and the edges of the cups are studded with tentacles, which +include fibro-vascular bundles, rather different from those seen by me in any +other species; for some of the vessels are barred and punctured, instead of +being spiral. The glands secrete copiously, judging from the quantity of dried +secretion adhering to them. [page 286] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0013" id="link2HCH0013"></a> +CHAPTER XIII.<br/> +DIONAEA MUSCIPULA.</h2> + +<p class="letter"> +Structure of the leaves—Sensitiveness of the filaments—Rapid +movement of the lobes caused by irritation of the filaments—Glands, their +power of secretion—Slow movement caused by the absorption of animal +matter—Evidence of absorption from the aggregated condition of the +glands—Digestive power of the secretion—Action of chloroform, +ether, and hydrocyanic acid—The manner in which insects are +captured—Use of the marginal spikes—Kinds of insects +captured—The transmission of the motor impulse and mechanism of the +movements—Re-expansion of the lobes. +</p> + +<p> +This plant, commonly called Venus’ fly-trap, from the rapidity and force +of its movements, is one of the most wonderful in the world.* It is a member of +the small family of the Droseraceae, and is found only in the eastern part of +North Carolina, growing in damp situations. The roots are small; those of a +moderately fine plant which I examined consisted of two branches about 1 inch +in length, springing from a bulbous enlargement. They probably serve, as in the +case of Drosera, solely for the absorption of water; for a gardener, who has +been very successful in the cultivation of this plant, grows it, like an +epiphytic orchid, in well-drained damp moss without any soil.** The form of the +bilobed leaf, with its foliaceous footstalk, is shown in the accompanying +drawing (fig. 12). +</p> + +<p class="footnote"> +* Dr. Hooker, in his address to the British Association at Belfast, 1874, has +given so full an historical account of the observations which have been +published on the habits of this plant, that it would be superfluous on my part +to repeat them. +</p> + +<p class="footnote"> +** ‘Gardener’s Chronicle,’ 1874, p. 464. [page 287] +</p> + +<p> +The two lobes stand at rather less than a right angle to each other. Three +minute pointed processes or filaments, placed triangularly, project from the +upper surfaces of both; but I have seen two leaves with four filaments on each +side, and another with only two. These filaments are remarkable from their +extreme sensitiveness to a touch, as shown not by their own movement, but by +that of the lobes. The margins of the leaf are prolonged into sharp rigid +projections which I will call spikes, into each of which a bundle +</p> + +<p> +FIG. 12. (Dionaea muscipula.) Leaf viewed laterally in its expanded state. +</p> + +<p> +of spiral vessels enters. The spikes stand in such a position that, when the +lobes close, they inter-lock like the teeth of a rat-trap. The midrib of the +leaf, on the lower side, is strongly developed and prominent. +</p> + +<p> +The upper surface of the leaf is thickly covered, excepting towards the +margins, with minute glands of a reddish or purplish colour, the rest of the +leaf being green. There are no glands on the spikes, or on the foliaceous +footstalk, The glands are formed of from [page 288] twenty to thirty polygonal +cells, filled with purple fluid. Their upper surface is convex. They stand on +very short pedicels, into which spiral vessels do not enter, in which respect +they differ from the tentacles of Drosera. They secrete, but only when excited +by the absorption of certain matters; and they have the power of absorption. +Minute projections, formed of eight divergent arms of a reddish-brown or orange +colour, and appearing under the microscope like elegant little flowers, are +scattered in considerable numbers over the foot-stalk, the backs of the leaves, +and the spikes, with a few on the upper surface of the lobes. These octofid +projections are no doubt homologous with the papillae on the leaves of Drosera +rotundifolia. There are also a few very minute, simple, pointed hairs, about +7/12000 (.0148 mm.) of an inch in length on the backs of the leaves. +</p> + +<p> +The sensitive filaments are formed of several rows of elongated cells, filled +with purplish fluid. They are a little above the 1/20 of an inch in length; are +thin and delicate, and taper to a point. I examined the bases of several, +making sections of them, but no trace of the entrance of any vessel could be +seen. The apex is sometimes bifid or even trifid, owing to a slight separation +between the terminal pointed cells. Towards the base there is constriction, +formed of broader cells, beneath which there is an articulation, supported on +an enlarged base, consisting of differently shaped polygonal cells. As the +filaments project at right angles to the surface of the leaf, they would have +been liable to be broken whenever the lobes closed together, had it not been +for the articulation which allows them to bend flat down. +</p> + +<p> +These filaments, from their tips to their bases, are exquisitely sensitive to a +momentary touch. It is scarcely [page 289] possible to touch them ever so +lightly or quickly with any hard object without causing the lobes to close. A +piece of very delicate human hair, 2 1/2 inches in length, held dangling over a +filament, and swayed to and fro so as to touch it, did not excite any movement. +But when a rather thick cotton thread of the same length was similarly swayed, +the lobes closed. Pinches of fine wheaten flour, dropped from a height, +produced no effect. The above-mentioned hair was then fixed into a handle, and +cut off so that 1 inch projected; this length being sufficiently rigid to +support itself in a nearly horizontal line. The extremity was then brought by a +slow movement laterally into contact with the tip of a filament, and the leaf +instantly closed. On another occasion two or three touches of the same kind +were necessary before any movement ensued. When we consider how flexible a fine +hair is, we may form some idea how slight must be the touch given by the +extremity of a piece, 1 inch in length, moved slowly. +</p> + +<p> +Although these filaments are so sensitive to a momentary and delicate touch, +they are far less sensitive than the glands of Drosera to prolonged pressure. +Several times I succeeded in placing on the tip of a filament, by the aid of a +needle moved with extreme slowness, bits of rather thick human hair, and these +did not excite movement, although they were more than ten times as long as +those which caused the tentacles of Drosera to bend; and although in this +latter case they were largely supported by the dense secretion. On the other +hand, the glands of Drosera may be struck with a needle or any hard object, +once, twice, or even thrice, with considerable force, and no movement ensues. +This singular difference in the nature of the sensitiveness of the filaments of +Dionaea and of [page 290] the glands of Drosera evidently stands in relation to +the habits of the two plants. If a minute insect alights with its delicate feet +on the glands of Drosera, it is caught by the viscid secretion, and the slight, +though prolonged pressure, gives notice of the presence of prey, which is +secured by the slow bending of the tentacles. On the other hand, the sensitive +filaments of Dionaea are not viscid, and the capture of insects can be assured +only by their sensitiveness to a momentary touch, followed by the rapid closure +of the lobes. +</p> + +<p> +As just stated, the filaments are not glandular, and do not secrete. Nor have +they the power of absorption, as may be inferred from drops of a solution of +carbonate of ammonia (one part to 146 of water), placed on two filaments, not +producing any effect on the contents of their cells, nor causing the lobes to +close, When, however, a small portion of a leaf with an attached filament was +cut off and immersed in the same solution, the fluid within the basal cells +became almost instantly aggregated into purplish or colourless, irregularly +shaped masses of matter. The process of aggregation gradually travelled up the +filaments from cell to cell to their extremities, that is in a reverse course +to what occurs in the tentacles of Drosera when their glands have been excited. +Several other filaments were cut off close to their bases, and left for 1 hr. +30 m. in a weaker solution of one part of the carbonate to 218 of water, and +this caused aggregation in all the cells, commencing as before at the bases of +the filaments. +</p> + +<p> +Long immersion of the filaments in distilled water likewise causes aggregation. +Nor is it rare to find the contents of a few of the terminal cells in a +spontaneously aggregated condition. The aggregated [page 291] masses undergo +incessant slow changes of form, uniting and again separating; and some of them +apparently revolve round their own axes. A current of colourless granular +protoplasm could also be seen travelling round the walls of the cells. This +current ceases to be visible as soon as the contents are well aggregated; but +it probably still continues, though no longer visible, owing to all the +granules in the flowing layer having become united with the central masses. In +all these respects the filaments of Dionaea behave exactly like the tentacles +of Drosera. +</p> + +<p> +Notwithstanding this similarity there is one remarkable difference. The +tentacles of Drosera, after their glands have been repeatedly touched, or a +particle of any kind has been placed on them, become inflected and strongly +aggregated. No such effect is produced by touching the filaments of Dionaea; I +compared, after an hour or two, some which had been touched and some which had +not, and others after twenty-five hours, and there was no difference in the +contents of the cells. The leaves were kept open all the time by clips; so that +the filaments were not pressed against the opposite lobe. +</p> + +<p> +Drops of water, or a thin broken stream, falling from a height on the +filaments, did not cause the blades to close; though these filaments were +afterwards proved to be highly sensitive. No doubt, as in the case of Drosera, +the plant is indifferent to the heaviest shower of rain. Drops of a solution of +a half an ounce of sugar to a fluid ounce of water were repeatedly allowed to +fall from a height on the filaments, but produced no effect, unless they +adhered to them. Again, I blew many times through a fine pointed tube with my +utmost force against the filaments without any effect; such blowing being +received [page 292] with as much indifference as no doubt is a heavy gale of +wind. We thus see that the sensitiveness of the filaments is of a specialised +nature, being related to a momentary touch rather than to prolonged pressure; +and the touch must not be from fluids, such as air or water, but from some +solid object. +</p> + +<p> +Although drops of water and of a moderately strong solution of sugar, falling +on the filaments, does not excite them, yet the immersion of a leaf in pure +water sometimes caused the lobes to close. One leaf was left immersed for 1 hr. +10 m., and three other leaves for some minutes, in water at temperatures +varying between 59° and 65° (15° to 18°.3 Cent.) without any effect. One, +however, of these four leaves, on being gently withdrawn from the water, closed +rather quickly. The three other leaves were proved to be in good condition, as +they closed when their filaments were touched. Nevertheless two fresh leaves on +being dipped into water at 75° and 62 1/2° (23°.8 and 16°.9 Cent.) instantly +closed. These were then placed with their footstalks in water, and after 23 +hrs. partially re-expanded; on touching their filaments one of them closed. +This latter leaf after an additional 24 hrs. again re-expanded, and now, on the +filaments of both leaves being touched, both closed. We thus see that a short +immersion in water does not at all injure the leaves, but sometimes excites the +lobes to close. The movement in the above cases was evidently not caused by the +temperature of the water. It has been shown that long immersion causes the +purple fluid within the cells of the sensitive filaments to become aggregated; +and the tentacles of Drosera are acted on in the same manner by long immersion, +often being somewhat inflected. In both cases the result is probably due to a +slight degree of exosmose. [page 293] +</p> + +<p> +I am confirmed in this belief by the effects of immersing a leaf of Dionaea in +a moderately strong solution of sugar; the leaf having been previously left for +1 hr. 10 m. in water without any effect; for now the lobes closed rather +quickly, the tips of the marginal spikes crossing in 2 m. 30 s., and the leaf +being completely shut in 3 m. Three leaves were then immersed in a solution of +half an ounce of sugar to a fluid ounce of water, and all three leaves closed +quickly. As I was doubtful whether this was due to the cells on the upper +surface of the lobes, or to the sensitive filaments, being acted on by +exosmose, one leaf was first tried by pouring a little of the same solution in +the furrow between the lobes over the midrib, which is the chief seat of +movement. It was left there for some time, but no movement ensued. The whole +upper surface of leaf was then painted (except close round the bases of the +sensitive filaments, which I could not do without risk of touching them) with +the same solution, but no effect was produced. So that the cells on the upper +surface are not thus affected. But when, after many trials, I succeeded in +getting a drop of the solution to cling to one of the filaments, the leaf +quickly closed. Hence we may, I think, conclude that the solution causes fluid +to pass out of the delicate cells of the filaments by exosmose; and that this +sets up some molecular change in their contents, analogous to that which must +be produced by a touch. +</p> + +<p> +The immersion of leaves in a solution of sugar affects them for a much longer +time than does an immersion in water, or a touch on the filaments; for in these +latter cases the lobes begin to re-expand in less than a day. On the other +hand, of the three leaves which were immersed for a short time in the solution, +and were then washed by means of a syringe inserted [page 294] between the +lobes, one re-expanded after two days; a second after seven days; and the third +after nine days. The leaf which closed, owing to a drop of the solution having +adhered to one of the filaments, opened after two days. +</p> + +<p> +I was surprised to find on two occasions that the heat from the rays of the +sun, concentrated by a lens on the bases of several filaments, so that they +were scorched and discoloured, did not cause any movement; though the leaves +were active, as they closed, though rather slowly, when a filament on the +opposite side was touched. On a third trial, a fresh leaf closed after a time, +though very slowly; the rate not being increased by one of the filaments, which +had not been injured, being touched. After a day these three leaves opened, and +were fairly sensitive when the uninjured filaments were touched. The sudden +immersion of a leaf into boiling water does not cause it to close. Judging from +the analogy of Drosera, the heat in these several cases was too great and too +suddenly applied. The surface of the blade is very slightly sensitive; It may +be freely and roughly handled, without any movement being caused. A leaf was +scratched rather hard with a needle, but did not close; but when the triangular +space between the three filaments on another leaf was similarly scratched, the +lobes closed. They always closed when the blade or midrib was deeply pricked or +cut. Inorganic bodies, even of large size, such as bits of stone, glass, +&c.—or organic bodies not containing soluble nitrogenous matter, such +as bits of wood, cork, moss,—or bodies containing soluble nitrogenous +matter, if perfectly dry, such as bits of meat, albumen, gelatine, &c., may +be long left (and many were tried) on the lobes, and no movement is excited. +The result, however, is widely different, as we [page 295] shall presently see, +if nitrogenous organic bodies which are at all damp, are left on the lobes; for +these then close by a slow and gradual movement, very different from that +caused by touching one of the sensitive filaments. The footstalk is not in the +least sensitive; a pin may be driven through it, or it may be cut off, and no +movement follows. +</p> + +<p> +The upper surface of the lobes, as already stated, is thickly covered with +small purplish, almost sessile glands. These have the power both of secretion +and absorption; but unlike those of Drosera, they do not secrete until excited +by the absorption of nitrogenous matter. No other excitement, as far as I have +seen, produces this effect. Objects, such as bits of wood, cork, moss, paper, +stone, or glass, may be left for a length of time on the surface of a leaf, and +it remains quite dry. Nor does it make any difference if the lobes close over +such objects. For instance, some little balls of blotting paper were placed on +a leaf, and a filament was touched; and when after 24 hrs. the lobes began to +re-open, the balls were removed by the aid of thin pincers, and were found +perfectly dry. On the other hand, if a bit of damp meat or a crushed fly is +placed on the surface of an expanded leaf, the glands after a time secrete +freely. In one such case there was a little secretion directly beneath the meat +in 4 hrs.; and after an additional 3 hrs. there was a considerable quantity +both under and close round it. In another case, after 3 hrs. 40 m., the bit of +meat was quite wet. But none of the glands secreted, excepting those which +actually touched the meat or the secretion containing dissolved animal matter. +</p> + +<p> +If, however, the lobes are made to close over a bit of meat or an insect, the +result is different, for the glands over the whole surface of the leaf now +secrete copiously. [page 296] As in this case the glands on both sides are +pressed against the meat or insect, the secretion from the first is twice as +great as when a bit of meat is laid on the surface of one lobe; and as the two +lobes come into almost close contact, the secretion, containing dissolved +animal matter, spreads by capillary attraction, causing fresh glands on both +sides to begin secreting in a continually widening circle. The secretion is +almost colourless, slightly mucilaginous, and, judging by the manner in which +it coloured litmus paper, more strongly acid than that of Drosera. It is so +copious that on one occasion, when a leaf was cut open, on which a small cube +of albumen had been placed 45 hrs. before, drops rolled off the leaf. On +another occasion, in which a leaf with an enclosed bit of roast meat +spontaneously opened after eight days, there was so much secretion in the +furrow over the midrib that it trickled down. A large crushed fly (Tipula) was +placed on a leaf from which a small portion at the base of one lobe had +previously been cut away, so that an opening was left; and through this, the +secretion continued to run down the footstalk during nine days,—that is, +for as long a time as it was observed. By forcing up one of the lobes, I was +able to see some distance between them, and all the glands within sight were +secreting freely. +</p> + +<p> +We have seen that inorganic and non-nitrogenous objects placed on the leaves do +not excite any movement; but nitrogenous bodies, if in the least degree damp, +cause after several hours the lobes to close slowly. Thus bits of quite dry +meat and gelatine were placed at opposite ends of the same leaf, and in the +course of 24 hrs. excited neither secretion nor movement. They were then dipped +in water, their surfaces dried on blotting paper, and replaced on the same +[page 297] leaf, the plant being now covered with a bell-glass. After 24 hrs. +the damp meat had excited some acid secretion, and the lobes at this end of the +leaf were almost shut. At the other end, where the damp gelatine lay, the leaf +was still quite open, nor had any secretion been excited; so that, as with +Drosera, gelatine is not nearly so exciting a substance as meat. The secretion +beneath the meat was tested by pushing a strip of litmus paper under it (the +filaments not being touched), and this slight stimulus caused the leaf to shut. +On the eleventh day it reopened; but the end where the gelatine lay, expanded +several hours before the opposite end with the meat. +</p> + +<p> +A second bit of roast meat, which appeared dry, though it had not been +purposely dried, was left for 24 hrs. on a leaf, caused neither movement nor +secretion. The plant in its pot was now covered with a bell-glass, and the meat +absorbed some moisture from the air; this sufficed to excite acid secretion, +and by the next morning the leaf was closely shut. A third bit of meat, dried +so as to be quite brittle, was placed on a leaf under a bell-glass, and this +also became in 24 hrs. slightly damp, and excited some acid secretion, but no +movement. +</p> + +<p> +A rather large piece of perfectly dry albumen was left at one end of a leaf for +24 hrs. without any effect. It was then soaked for a few minutes in water, +rolled about on blotting paper, and replaced on the leaf; in 9 hrs. some +slightly acid secretion was excited, and in 24 hrs. this end of the leaf was +partially closed. The bit of albumen, which was now surrounded by much +secretion, was gently removed, and although no filament was touched, the lobes +closed. In this and the previous case, it appears that the absorption of animal +matter by the glands renders [page 298] the surface of the leaf much more +sensitive to a touch than it is in its ordinary state; and this is a curious +fact. Two days afterwards the end of the leaf where nothing had been placed +began to open, and on the third day was much more open than the opposite end +where the albumen had lain. +</p> + +<p> +Lastly, large drops of a solution of one part of carbonate of ammonia to 146 of +water were placed on some leaves, but no immediate movement ensued. I did not +then know of the slow movement caused by animal matter, otherwise I should have +observed the leaves for a longer time, and they would probably have been found +closed, though the solution (judging from Drosera) was, perhaps, too strong. +</p> + +<p> +From the foregoing cases it is certain that bits of meat and albumen, if at all +damp, excite not only the glands to secrete, but the lobes to close. This +movement is widely different from the rapid closure caused by one of the +filaments being touched. We shall see its importance when we treat of the +manner in which insects are captured. There is a great contrast between Drosera +and Dionaea in the effects produced by mechanical irritation on the one hand, +and the absorption of animal matter on the other. Particles of glass placed on +the glands of the exterior tentacles of Drosera excite movement within nearly +the same time, as do particles of meat, the latter being rather the most +efficient; but when the glands of the disc have bits of meat given them, they +transmit a motor impulse to the exterior tentacles much more quickly than do +these glands when bearing inorganic particles, or when irritated by repeated +touches. On the other hand, with Dionaea, touching the filaments excites +incomparably quicker movement than the absorption of animal matter by the +glands. Nevertheless, in [page 299] certain cases, this latter stimulus is the +more powerful of the two. On three occasions leaves were found which from some +cause were torpid, so that their lobes closed only slightly, however much their +filaments were irritated; but on inserting crushed insects between the lobes, +they became in a day closely shut. +</p> + +<p> +The facts just given plainly show that the glands have the power of absorption, +for otherwise it is impossible that the leaves should be so differently +affected by non-nitrogenous and nitrogenous bodies, and between these latter in +a dry and damp condition. It is surprising how slightly damp a bit of meat or +albumen need be in order to excite secretion and afterwards slow movement, and +equally surprising how minute a quantity of animal matter, when absorbed, +suffices to produce these two effects. It seems hardly credible, and yet it is +certainly a fact, that a bit of hard-boiled white of egg, first thoroughly +dried, then soaked for some minutes in water and rolled on blotting paper, +should yield in a few hours enough animal matter to the glands to cause them to +secrete, and afterwards the lobes to close. That the glands have the power of +absorption is likewise shown by the very different lengths of time (as we shall +presently see) during which the lobes remain closed over insects and other +bodies yielding soluble nitrogenous matter, and over such as do not yield any. +But there is direct evidence of absorption in the condition of the glands which +have remained for some time in contact with animal matter. Thus bits of meat +and crushed insects were several times placed on glands, and these were +compared after some hours with other glands from distant parts of the same +leaf. The latter showed not a trace of aggregation, whereas those which had +been in contact with the animal matter were [page 300] well aggregated. +Aggregation may be seen to occur very quickly if a piece of a leaf is immersed +in a weak solution of carbonate of ammonia. Again, small cubes of albumen and +gelatine were left for eight days on a leaf, which was then cut open. The whole +surface was bathed with acid secretion, and every cell in the many glands which +were examined had its contents aggregated in a beautiful manner into dark or +pale purple, or colourless globular masses of protoplasm. These underwent +incessant slow changes of forms; sometimes separating from one another and then +reuniting, exactly as in the cells of Drosera. Boiling water makes the contents +of the gland-cells white and opaque, but not so purely white and porcelain-like +as in the case of Drosera. How living insects, when naturally caught, excite +the glands to secrete so quickly as they do, I know not; but I suppose that the +great pressure to which they are subjected forces a little excretion from +either extremity of their bodies, and we have seen that an extremely small +amount of nitrogenous matter is sufficient to excite the glands. +</p> + +<p> +Before passing on to the subject of digestion, I may state that I endeavoured +to discover, with no success, the functions of the minute octofid processes +with which the leaves are studded. From facts hereafter to be given in the +chapters on Aldrovanda and Utricularia, it seemed probable that they served to +absorb decayed matter left by the captured insects; but their position on the +backs of the leaves and on the footstalks rendered this almost impossible. +Nevertheless, leaves were immersed in a solution of one part of urea to 437 of +water, and after 24 hrs. the orange layer of protoplasm within the arms of +these processes did not appear more aggregated than in other speci- [page 301] +mens kept in water, I then tried suspending a leaf in a bottle over an +excessively putrid infusion of raw meat, to see whether they absorbed the +vapour, but their contents were not affected. +</p> + +<p> +Digestive Power of the Secretion.*—When a leaf closes over any object, it +may be said to form itself into a temporary stomach; and if the object yields +ever so little animal matter, this serves, to use Schiff’s expression, as +a peptogene, and the glands on the surface pour forth their acid secretion, +which acts like the gastric juice of animals. As so many experiments were tried +on the digestive power of Drosera, only a few were made with Dionaea, but they +were amply sufficient to prove that it digests, This plant, moreover, is not so +well fitted as Drosera for observation, as the process goes on within the +closed lobes. Insects, even beetles, after being subjected to the secretion for +several days, are surprisingly softened, though their chitinous coats are not +corroded, +</p> + +<p> +[Experiment 1.—A cube of albumen of 1/10 of an inch (2.540 mm.) was +placed at one end of a leaf, and at the other end an oblong piece of gelatine, +1/5 of an inch (5.08 mm.) long, and +</p> + +<p class="footnote"> +* Dr. W.M. Canby, of Wilmington, to whom I am much indebted for information +regarding Dionaea in its native home, has published in the +‘Gardener’s Monthly,’ Philadelphia, August 1868, some +interesting observations. He ascertained that the secretion digests animal +matter, such as the contents of insects, bits of meat, &c.; and that the +secretion is reabsorbed. He was also well aware that the lobes remain closed +for a much longer time when in contact with animal matter than when made to +shut by a mere touch, or over objects not yielding soluble nutriment; and that +in these latter cases the glands do not secrete. The Rev. Dr. Curtis first +observed (‘Boston Journal Nat. Hist.’ vol. i., p. 123) the +secretion from the glands. I may here add that a gardener, Mr. Knight, is said +(Kirby and Spencer’s ‘Introduction to Entomology,’ 1818, vol. +i., p. 295) to have found that a plant of the Dionaea, on the leaves of which +“he laid fine filaments of raw beef, was much more luxuriant in its +growth than others not so treated.” [page 302] +</p> + +<p> +1/10 broad; the leaf was then made to close. It was cut open after 45 hrs. The +albumen was hard and compressed, with its angles only a little rounded; the +gelatine was corroded into an oval form; and both were bathed in so much acid +secretion that it dropped off the leaf. The digestive process apparently is +rather slower than in Drosera, and this agrees with the length of time during +which the leaves remain closed over digestible objects. +</p> + +<p> +Experiment 2.—A bit of albumen 1/10 of an inch square, but only 1/20 in +thickness, and a piece of gelatine of the same size as before, were placed on a +leaf, which eight days afterwards was cut open. The surface was bathed with +slightly adhesive, very acid secretion, and the glands were all in an +aggregated condition. Not a vestige of the albumen or gelatine was left. +Similarly sized pieces were placed at the same time on wet moss on the same +pot, so that they were subjected to nearly similar conditions; after eight days +these were brown, decayed, and matted with fibres of mould, but had not +disappeared. +</p> + +<p> +Experiment 3.—A piece of albumen 3/20 of an inch (3.81 mm.) long, and +1/20 broad and thick, and a piece of gelatine of the same size as before, were +placed on another leaf, which was cut open after seven days; not a vestige of +either substance was left, and only a moderate amount of secretion on the +surface. +</p> + +<p> +Experiment 4.—Pieces of albumen and gelatine, of the same size as in the +last experiment, were placed on a leaf, which spontaneously opened after twelve +days, and here again not a vestige of either was left, and only a little +secretion at one end of the midrib. +</p> + +<p> +Experiment 5.—Pieces of albumen and gelatine of the same size were placed +on another leaf, which after twelve days was still firmly closed, but had begun +to wither; it was cut open, and contained nothing except a vestige of brown +matter where the albumen had lain. +</p> + +<p> +Experiment 6.—A cube of albumen of 1/10 of an inch and a piece of +gelatine of the same size as before were placed on a leaf, which opened +spontaneously after thirteen days, The albumen, which was twice as thick as in +the latter experiments, was too large; for the glands in contact with it were +injured and were dropping off; a film also of albumen of a brown colour, matted +with mould, was left. All the gelatine was absorbed, and there was only a +little acid secretion left on the midrib. +</p> + +<p> +Experiment 7.—A bit of half roasted meat (not measured) and a bit of +gelatine were placed on the two ends of a leaf, which [page 303] opened +spontaneously after eleven days; a vestige of the meat was left, and the +surface of the leaf was here blackened; the gelatine had all disappeared. +</p> + +<p> +Experiment 8.—A bit of half roasted meat (not measured) was placed on a +leaf which was forcibly kept open by a clip, so that it was moistened with the +secretion (very acid) only on its lower surface. Nevertheless, after only 22 +1/2 hrs. it was surprisingly softened, when compared with another bit of the +same meat which had been kept damp. +</p> + +<p> +Experiment 9.—A cube of 1/10 of an inch of very compact roasted beef was +placed on a leaf, which opened spontaneously after twelve days; so much feebly +acid secretion was left on the leaf that it trickled off. The meat was +completely disintegrated, but not all dissolved; there was no mould. The little +mass was placed under the microscope; some of the fibrillae in the middle still +exhibited transverse striae; others showed not a vestige of striae; and every +gradation could be traced between these two states. Globules, apparently of +fat, and some undigested fibro-elastic tissue remained. The meat was thus in +the same state as that formerly described, which was half digested by Drosera. +Here, again, as in the case of albumen, the digestive process seems slower than +in Drosera. At the opposite end of the same leaf, a firmly compressed pellet of +bread had been placed; this was completely disintegrated, I suppose, owing to +the digestion of the gluten, but seemed very little reduced in bulk. +</p> + +<p> +Experiment 10.—A cube of 1/20 of an inch of cheese and another of albumen +were placed at opposite ends of the same leaf. After nine days the lobes opened +spontaneously a little at the end enclosing the cheese, but hardly any or none +was dissolved, though it was softened and surrounded by secretion. Two days +subsequently the end with the albumen also opened spontaneously (i.e. eleven +days after it was put on), a mere trace in a blackened and dry condition being +left. +</p> + +<p> +Experiment 11.—The same experiment with cheese and albumen repeated on +another and rather torpid leaf. The lobes at the end with the cheese, after an +interval of six days, opened spontaneously a little; the cube of cheese was +much softened, but not dissolved, and but little, if at all, reduced in size. +Twelve hours afterwards the end with the albumen opened, which now consisted of +a large drop of transparent, not acid, viscid fluid. +</p> + +<p> +Experiment 12.—Same experiment as the two last, and here again the leaf +at the end enclosing the cheese opened before the [page 304] opposite end with +the albumen; but no further observations were made. +</p> + +<p> +Experiment 13.—A globule of chemically prepared casein, about 1/10 of an +inch in diameter, was placed on a leaf, which spontaneously opened after eight +days. The casein now consisted of a soft sticky mass, very little, if at all, +reduced in size, but bathed in acid secretion.] +</p> + +<p> +These experiments are sufficient to show that the secretion from the glands of +Dionaea dissolves albumen, gelatine, and meat, if too large pieces are not +given. Globules of fat and fibro-elastic tissue are not digested. The +secretion, with its dissolved matter, if not in excess, is subsequently +absorbed. On the other hand, although chemically prepared casein and cheese (as +in the case of Drosera) excite much acid secretion, owing, I presume, to the +absorption of some included albuminous matter, these substances are not +digested, and are not appreciably, if at all, reduced in bulk. +</p> + +<p> +[Effects of the Vapours of Chloroform, Sulphuric Ether, and Hydrocyanic +Acid.—A plant bearing one leaf was introduced into a large bottle with a +drachm (3.549 ml.) of chloroform, the mouth being imperfectly closed with +cotton-wool. The vapour caused in 1 m. the lobes to begin moving at an +imperceptibly slow rate; but in 3 m. the spikes crossed, and the leaf was soon +completely shut. The dose, however, was much too large, for in between 2 and 3 +hrs. the leaf appeared as if burnt, and soon died. +</p> + +<p> +Two leaves were exposed for 30 m. in a 2-oz: vessel to the vapour of 30 minims +(1.774 ml.) of sulphuric ether. One leaf closed after a time, as did the other +whilst being removed from the vessel without being touched. Both leaves were +greatly injured. Another leaf, exposed for 20 m. to 15 minims of ether, closed +its lobes to a certain extent, and the sensitive filaments were now quite +insensible. After 24 hrs. this leaf recovered its sensibility, but was still +rather torpid. A leaf exposed in a large bottle for only 3 m. to ten drops was +rendered insensible. After 52 m. it recovered its sensibility, and when one of +the filaments was touched, the lobes closed. It began [page 305] to reopen +after 20 hrs. Lastly another leaf was exposed for 4 m. to only four drops of +the ether; it was rendered insensible, and did not close when its filaments +were repeatedly touched, but closed when the end of the open leaf was cut off. +This shows either that the internal parts had not been rendered insensible, or +that an incision is a more powerful stimulus than repeated touches on the +filaments. Whether the larger doses of chloroform and ether, which caused the +leaves to close slowly, acted on the sensitive filaments or on the leaf itself, +I do not know. +</p> + +<p> +Cyanide of potassium, when left in a bottle, generates prussic or hydrocyanic +acid. A leaf was exposed for 1 hr. 35 m. to the vapour thus formed; and the +glands became within this time so colourless and shrunken as to be scarcely +visible, and I at first thought that they had all dropped off. The leaf was not +rendered insensible; for as soon as one of the filaments was touched it closed. +It had, however, suffered, for it did not reopen until nearly two days had +passed, and was not even then in the least sensitive. After an additional day +it recovered its powers, and closed on being touched and subsequently reopened. +Another leaf behaved in nearly the same manner after a shorter exposure to this +vapour.] +</p> + +<p> +On the Manner in which Insects are caught.—We will now consider the +action of the leaves when insects happen to touch one of the sensitive +filaments. This often occurred in my greenhouse, but I do not know whether +insects are attracted in any special way by the leaves. They are caught in +large numbers by the plant in its native country. As soon as a filament is +touched, both lobes close with astonishing quickness; and as they stand at less +than a right angle to each other, they have a good chance of catching any +intruder. The angle between the blade and footstalk does not change when the +lobes close. The chief seat of movement is near the midrib, but is not confined +to this part; for, as the lobes come together, each curves inwards across its +whole breadth; the marginal spikes however, not becoming curved. This move- +[page 306] ment of the whole lobe was well seen in a leaf to which a large fly +had been given, and from which a large portion had been cut off the end of one +lobe; so that the opposite lobe, meeting with no resistance in this part, went +on curving inwards much beyond the medial line. The whole of the lobe, from +which a portion had been cut, was afterwards removed, and the opposite lobe now +curled completely over, passing through an angle of from 120o to 130o, so as to +occupy a position almost at right angles to that which it would have held had +the opposite lobe been present. +</p> + +<p> +From the curving inwards of the two lobes, as they move towards each other, the +straight marginal spikes intercross by their tips at first, and ultimately by +their bases. The leaf is then completely shut and encloses a shallow cavity. If +it has been made to shut merely by one of the sensitive filaments having been +touched, or if it includes an object not yielding soluble nitrogenous matter, +the two lobes retain their inwardly concave form until they re-expand. The +re-expansion under these circumstances—that is when no organic matter is +enclosed—was observed in ten cases. In all of these, the leaves +re-expanded to about two-thirds of the full extent in 24 hrs. from the time of +closure. Even the leaf from which a portion of one lobe had been cut off opened +to a slight degree within this same time. In one case a leaf re-expanded to +about two-thirds of the full extent in 7 hrs., and completely in 32 hrs.; but +one of its filaments had been touched merely with a hair just enough to cause +the leaf to close. Of these ten leaves only a few re-expanded completely in +less than two days, and two or three required even a little longer time. +Before, however, they fully re-expand, they are ready to close [page 307] +instantly if their sensitive filaments are touched. How many times a leaf is +capable of shutting and opening if no animal matter is left enclosed, I do not +know; but one leaf was made to close four times, reopening afterwards, within +six days, On the last occasion it caught a fly, and then remained closed for +many days. +</p> + +<p> +This power of reopening quickly after the filaments have been accidentally +touched by blades of grass, or by objects blown on the leaf by the wind, as +occasionally happens in its native place,* must be of some importance to the +plant; for as long as a leaf remains closed, it cannot of course capture an +insect. +</p> + +<p> +When the filaments are irritated and a leaf is made to shut over an insect, a +bit of meat, albumen, gelatine, casein, and, no doubt, any other substance +containing soluble nitrogenous matter, the lobes, instead of remaining concave, +thus including a concavity, slowly press closely together throughout their +whole breadth. As this takes place, the margins gradually become a little +everted, so that the spikes, which at first intercrossed, at last project in +two parallel rows. The lobes press against each other with such force that I +have seen a cube of albumen much flattened, with distinct impressions of the +little prominent glands; but this latter circumstance may have been partly +caused by the corroding action of the secretion. So firmly do they become +pressed together that, if any large insect or other object has been caught, a +corresponding projection on the outside of the leaf is distinctly visible. When +the two lobes are thus completely shut, they +</p> + +<p class="footnote"> +* According to Dr. Curtis, in ‘Boston Journal of Nat. Hist,’ vol. i +1837, p. 123. [page 308] +</p> + +<p> +resist being opened, as by a thin wedge driven between them, with astonishing +force, and are generally ruptured rather than yield. If not ruptured, they +close again, as Dr. Canby informs me in a letter, “with quite a loud +flap.” But if the end of a leaf is held firmly between the thumb and +finger, or by a clip, so that the lobes cannot begin to close, they exert, +whilst in this position, very little force. +</p> + +<p> +I thought at first that the gradual pressing together of the lobes was caused +exclusively by captured insects crawling over and repeatedly irritating the +sensitive filaments; and this view seemed the more probable when I learnt from +Dr. Burdon Sanderson that whenever the filaments of a closed leaf are +irritated, the normal electric current is disturbed. Nevertheless, such +irritation is by no means necessary, for a dead insect, or a bit of meat, or of +albumen, all act equally well; proving that in these cases it is the absorption +of animal matter which excites the lobes slowly to press close together. We +have seen that the absorption of an extremely small quantity of such matter +also causes a fully expanded leaf to close slowly; and this movement is clearly +analogous to the slow pressing together of the concave lobes. This latter +action is of high functional importance to the plant, for the glands on both +sides are thus brought into contact with a captured insect, and consequently +secrete. The secretion with animal matter in solution is then drawn by +capillary attraction over the whole surface of the leaf, causing all the glands +to secrete and allowing them to absorb the diffused animal matter. The +movement, excited by the absorption of such matter, though slow, suffices for +its final purpose, whilst the movement excited by one of the sensitive +filaments being touched is rapid, and this is indis- [page 309] pensable for +the capturing of insects. These two movements, excited by two such widely +different means, are thus both well adapted, like all the other functions of +the plant, for the purposes which they subserve. +</p> + +<p> +There is another wide difference in the action of leaves which enclose objects, +such as bits of wood, cork, balls of paper, or which have had their filaments +merely touched, and those which enclose organic bodies yielding soluble +nitrogenous matter. In the former case the leaves, as we have seen, open in +under 24 hrs. and are then ready, even before being fully-expanded, to shut +again. But if they have closed over nitrogen-yielding bodies, they remain +closely shut for many days; and after re-expanding are torpid, and never act +again, or only after a considerable interval of time. In four instances, leaves +after catching insects never reopened, but began to wither, remaining +closed—in one case for fifteen days over a fly; in a second, for +twenty-four days, though the fly was small; in a third for twenty-four days +over a woodlouse; and in a fourth, for thirty-five days over a large Tipula. In +two other cases leaves remained closed for at least nine days over flies, and +for how many more I do not know. It should, however, be added that in two +instances in which very small insects had been naturally caught the leaf opened +as quickly as if nothing had been caught; and I suppose that this was due to +such small insects not having been crushed or not having excreted any animal +matter, so that the glands were not excited. Small angular bits of albumen and +gelatine were placed at both ends of three leaves, two of which remained closed +for thirteen and the other for twelve days. Two other leaves remained closed +over bits of [page 310] meat for eleven days, a third leaf for eight days, and +a fourth (but this had been cracked and injured) for only six days. Bits of +cheese, or casein, were placed at one end and albumen at the other end of three +leaves; and the ends with the former opened after six, eight, and nine days, +whilst the opposite ends opened a little later. None of the above bits of meat, +albumen, &c., exceeded a cube of 1/10 of an inch (2.54 mm.) in size, and +were sometimes smaller; yet these small portions sufficed to keep the leaves +closed for many days. Dr. Canby informs me that leaves remain shut for a longer +time over insects than over meat; and from what I have seen, I can well believe +that this is the case, especially if the insects are large. +</p> + +<p> +In all the above cases, and in many others in which leaves remained closed for +a long but unknown period over insects naturally caught, they were more or less +torpid when they reopened. Generally they were so torpid during many succeeding +days that no excitement of the filaments caused the least movement. In one +instance, however, on the day after a leaf opened which had clasped a fly, it +closed with extreme slowness when one of its filaments was touched; and +although no object was left enclosed, it was so torpid that it did not re-open +for the second time until 44 hrs. had elapsed. In a second case, a leaf which +had expanded after remaining closed for at least nine days over a fly, when +greatly irritated, moved one alone of its two lobes, and retained this unusual +position for the next two days. A third case offers the strongest exception +which I have observed; a leaf, after remaining clasped for an unknown time over +a fly, opened, and when one of its filaments was touched, closed, though rather +slowly. Dr. Canby, [page 311] who observed in the United States a large number +of plants which, although not in their native site, were probably more vigorous +than my plants, informs me that he has “several times known vigorous +leaves to devour their prey several times; but ordinarily twice, or, quite +often, once was enough to render them unserviceable.” Mrs. Treat, who +cultivated many plants in New Jersey, also informs me that “several +leaves caught successively three insects each, but most of them were not able +to digest the third fly, but died in the attempt. Five leaves, however, +digested each three flies, and closed over the fourth, but died soon after the +fourth capture. Many leaves did not digest even one large insect.” It +thus appears that the power of digestion is somewhat limited, and it is certain +that leaves always remain clasped for many days over an insect, and do not +recover their power of closing again for many subsequent days. In this respect +Dionaea differs from Drosera, which catches and digests many insects after +shorter intervals of time. +</p> + +<p> +We are now prepared to understand the use of the marginal spikes, which form so +conspicuous a feature in the appearance of the plant (fig. 12, p. 287), and +which at first seemed to me in my ignorance useless appendages. From the inward +curvature of the lobes as they approach each other, the tips of the marginal +spikes first intercross, and ultimately their bases. Until the edges of the +lobes come into contact, elongated spaces between the spikes, varying from the +1/15 to the 1/10 of an inch (1.693 to 2.54 mm.) in breadth, according to the +size of the leaf, are left open. Thus an insect, if its body is not thicker +than these measurements, can easily escape between the crossed spikes, when +disturbed by the closing lobes and in- [page 312] creasing darkness; and one of +my sons actually saw a small insect thus escaping. A moderately large insect, +on the other hand, if it tries to escape between the bars will surely be pushed +back again into its horrid prison with closing walls, for the spikes continue +to cross more and more until the edges of the lobes come into contact. A very +strong insect, however, would be able to free itself, and Mrs. Treat saw this +effected by a rose-chafer (Macrodactylus subspinosus) in the United States. Now +it would manifestly be a great disadvantage to the plant to waste many days in +remaining clasped over a minute insect, and several additional days or weeks in +afterwards recovering its sensibility; inasmuch as a minute insect would afford +but little nutriment. It would be far better for the plant to wait for a time +until a moderately large insect was captured, and to allow all the little ones +to escape; and this advantage is secured by the slowly intercrossing marginal +spikes, which act like the large meshes of a fishing-net, allowing the small +and useless fry to escape. +</p> + +<p> +As I was anxious to know whether this view was correct—and as it seems a +good illustration of how cautious we ought to be in assuming, as I had done +with respect to the marginal spikes, that any fully developed structure is +useless—I applied to Dr. Canby. He visited the native site of the plant, +early in the season, before the leaves had grown to their full size, and sent +me fourteen leaves, containing naturally captured insects. Four of these had +caught rather small insects, viz. three of them ants, and the fourth a rather +small fly, but the other ten had all caught large insects, namely, five +elaters, two chrysomelas, a curculio, a thick and broad spider, and a +scolopendra. Out of these ten insects, no less than eight [page 313] were +beetles,* and out of the whole fourteen there was only one, viz. a dipterous +insect, which could readily take flight. Drosera, on the other hand, lives +chiefly on insects which are good flyers, especially Diptera, caught by the aid +of its viscid secretion. But what most concerns us is the size of the ten +larger insects. Their average length from head to tail was .256 of an inch, the +lobes of the leaves being on an average .53 of an inch in length, so that the +insects were very nearly half as long as the leaves within which they were +enclosed. Only a few of these leaves, therefore, had wasted their powers by +capturing small prey, though it is probable that many small insects had crawled +over them and been caught, but had then escaped through the bars. +</p> + +<p> +The Transmission of the Motor Impulse, and Means of Movement.—It is +sufficient to touch any one of the six filaments to cause both lobes to close, +these becoming at the same time incurved throughout their whole breadth. The +stimulus must therefore radiate in all directions from any one filament. It +must also be transmitted with much rapidity across the leaf, for in all +ordinary cases both lobes close simultaneously, as far as the eye can judge. +Most physiologists believe that in irritable plants the excitement is +transmitted along, or in close connection with, the fibro-vascular bundles. In +Dionaea, the course of these vessels (composed of spiral and ordinary vascular +</p> + +<p class="footnote"> +* Dr. Canby remarks (‘Gardener’s Monthly,’ August 1868), +“as a general thing beetles and insects of that kind, though always +killed, seem to be too hard-shelled to serve as food, and after a short time +are rejected.” I am surprised at this statement, at least with respect to +such beetles as elaters, for the five which I examined were in an extremely +fragile and empty condition, as if all their internal parts had been partially +digested. Mrs. Treat informs me that the plants which she cultivated in New +Jersey chiefly caught Diptera. [page 314] +</p> + +<p> +tissue) seems at first sight to favour this belief; for they run up the midrib +in a great bundle, sending off small bundles almost at right angles on each +side. These bifurcate occasionally as they extend towards the margin, and close +to the margin small branches from adjoining vessels unite and enter the +marginal spikes. At some of these points of union the vessels form curious +loops, like those described under Drosera. A continuous zigzag line of vessels +thus runs round the whole circumference of the leaf, and in the midrib all the +vessels are in close contact; so that all parts of the leaf seem to be brought +into some degree of communication. Nevertheless, the presence of vessels is not +necessary for the transmission of the motor impulse, for it is transmitted from +the tips of the sensitive filaments (these being about the 1/20 of an inch in +length), into which no vessels enter; and these could not have been overlooked, +as I made thin vertical sections of the leaf at the bases of the filaments. +</p> + +<p> +On several occasions, slits about the 1/10 of an inch in length were made with +a lancet, close to the bases of the filaments, parallel to the midrib, and, +therefore, directly across the course of the vessels. These were made sometimes +on the inner and sometimes on the outer sides of the filaments; and after +several days, when the leaves had reopened, these filaments were touched +roughly (for they were always rendered in some degree torpid by the operation), +and the lobes then closed in the ordinary manner, though slowly, and sometimes +not until after a considerable interval of time. These cases show that the +motor impulse is not transmitted along the vessels, and they further show that +there is no necessity for a direct line of communication from the filament +which is [page 315] touched towards the midrib and opposite lobe, or towards +the outer parts of the same lobe. +</p> + +<p> +Two slits near each other, both parallel to the midrib, were next made in the +same manner as before, one on each side of the base of a filament, on five +distinct leaves, so that a little slip bearing a filament was connected with +the rest of the leaf only at its two ends. These slips were nearly of the same +size; one was carefully measured; it was .12 of an inch (3.048 mm.) in length, +and .08 of an inch (2.032 mm.) in breadth; and in the middle stood the +filament. Only one of these slips withered and perished. After the leaf had +recovered from the operation, though the slits were still open, the filaments +thus circumstanced were roughly touched, and both lobes, or one alone, slowly +closed. In two instances touching the filament produced no effect; but when the +point of a needle was driven into the slip at the base of the filament, the +lobes slowly closed. Now in these cases the impulse must have proceeded along +the slip in a line parallel to the midrib, and then have radiated forth, either +from both ends or from one end alone of the slip, over the whole surface of the +two lobes. +</p> + +<p> +Again, two parallel slits, like the former ones, were made, one on each side of +the base of a filament, at right angles to the midrib. After the leaves (two in +number) had recovered, the filaments were roughly touched, and the lobes slowly +closed; and here the impulse must have travelled for a short distance in a line +at right angles to the midrib, and then have radiated forth on all sides over +both lobes. These several cases prove that the motor impulse travels in all +directions through the cellular tissue, independently of the course of the +vessels. +</p> + +<p> +With Drosera we have seen that the motor impulse [page 316] is transmitted in +like manner in all directions through the cellular tissue; but that its rate is +largely governed by the length of the cells and the direction of their longer +axes. Thin sections of a leaf of Dionaea were made by my son, and the cells, +both those of the central and of the more superficial layers, were found much +elongated, with their longer axes directed towards the midrib; and it is in +this direction that the motor impulse must be sent with great rapidity from one +lobe to the other, as both close simultaneously. The central parenchymatous +cells are larger, more loosely attached together, and have more delicate walls +than the more superficial cells. A thick mass of cellular tissue forms the +upper surface of the midrib over the great central bundle of vessels. +</p> + +<p> +When the filaments were roughly touched, at the bases of which slits had been +made, either on both sides or on one side, parallel to the midrib or at right +angles to it, the two lobes, or only one, moved. In one of these cases, the +lobe on the side which bore the filament that was touched moved, but in three +other cases the opposite lobe alone moved; so that an injury which was +sufficient to prevent a lobe moving did not prevent the transmission from it of +a stimulus which excited the opposite lobe to move. We thus also learn that, +although normally both lobes move together, each has the power of independent +movement. A case, indeed, has already been given of a torpid leaf that had +lately re-opened after catching an insect, of which one lobe alone moved when +irritated. Moreover, one end of the same lobe can close and re- expand, +independently of the other end, as was seen in some of the foregoing +experiments. +</p> + +<p> +When the lobes, which are rather thick, close, no trace of wrinkling can be +seen on any part of their upper [page 317] surfaces, It appears therefore that +the cells must contract. The chief seat of the movement is evidently in the +thick mass of cells which overlies the central bundle of vessels in the midrib. +To ascertain whether this part contracts, a leaf was fastened on the stage of +the microscope in such a manner that the two lobes could not become quite shut, +and having made two minute black dots on the midrib, in a transverse line and a +little towards one side, they were found by the micrometer to be 17/1000 of an +inch apart. One of the filaments was then touched and the lobes closed; but as +they were prevented from meeting, I could still see the two dots, which now +were 15/1000 of an inch apart, so that a small portion of the upper surface of +the midrib had contracted in a transverse line 2/1000 of an inch (.0508 mm.). +</p> + +<p> +We know that the lobes, whilst closing, become slightly incurved throughout +their whole breadth. This movement appears to be due to the contraction of the +superficial layers of cells over the whole upper surface. In order to observe +their contraction, a narrow strip was cut out of one lobe at right angles to +the midrib, so that the surface of the opposite lobe could be seen in this part +when the leaf was shut. After the leaf had recovered from the operation and had +re-expanded, three minute black dots were made on the surface opposite to the +slit or window, in a line at right angles to the midrib. The distance between +the dots was found to be 40/1000 of an inch, so that the two extreme dots were +80/1000 of an inch apart. One of the filaments was now touched and the leaf +closed. On again measuring the distances between the dots, the two next to the +midrib were nearer together by 1 to 2/1000 of an inch, and the two further dots +by 3 to 4/1000 of an inch, than they were before; so that the two extreme [page +318] dots now stood about 5/1000 of an inch (.127 mm.) nearer together than +before. If we suppose the whole upper surface of the lobe, which was 400/1000 +of an inch in breadth, to have contracted in the same proportion, the total +contraction will have amounted to about 25/1000 or 1/40 of an inch (.635 mm.); +but whether this is sufficient to account for the slight inward curvature of +the whole lobe, I am unable to say. +</p> + +<p> +Finally, with respect to the movement of the leaves, the wonderful discovery +made by Dr. Burdon Sanderson* is now universally known; namely that there +exists a normal electrical current in the blade and footstalk; and that when +the leaves are irritated, the current is disturbed in the same manner as takes +place during the contraction of the muscle of an animal. +</p> + +<p> +The Re-expansion of the Leaves.—This is effected at an insensibly slow +rate, whether or not any object is enclosed.** One lobe can re-expand by +itself, as occurred with the torpid leaf of which one lobe alone had closed. We +have also seen in the experiments with cheese and albumen that the two ends of +the same lobe can re-expand to a certain extent independently of each other. +But in all ordinary cases both lobes open at the same time. The re-expansion is +not determined by the sensitive filaments; all three filaments on one lobe were +cut off close to their bases; and the three +</p> + +<p class="footnote"> +* Proc. Royal Soc.’ vol. xxi. p. 495; and lecture at the Royal +Institution, June 5, 1874, given in ‘Nature,’ 1874, pp. 105 and +127. +</p> + +<p class="footnote"> +** Nuttall, in his ‘Gen. American Plants,’ p. 277 (note), says +that, whilst collecting this plant in its native home, “I had occasion to +observe that a detached leaf would make repeated efforts towards disclosing +itself to the influence of the sun; these attempts consisted in an undulatory +motion of the marginal ciliae, accompanied by a partial opening and succeeding +collapse of the lamina, which at length terminated in a complete expansion and +in the destruction of sensibility.” I am indebted to Prof. Oliver for +this reference; but I do not understand what took place. [page 319] +</p> + +<p> +leaves thus treated re-expanded,—one to a partial extent in 24 +hrs.,—a second to the same extent in 48 hrs., and the third, which had +been previously injured, not until the sixth day. These leaves after their +re-expansion closed quickly when the filaments on the other lobe were +irritated. These were then cut off one of the leaves, so that none were left. +This mutilated leaf, notwithstanding the loss of all its filaments, re-expanded +in two days in the usual manner. When the filaments have been excited by +immersion in a solution of sugar, the lobes do not expand so soon as when the +filaments have been merely touched; and this, I presume, is due to their having +been strongly affected through exosmose, so that they continue for some time to +transmit a motor impulse to the upper surface of the leaf. +</p> + +<p> +The following facts make me believe that the several layers of cells forming +the lower surface of the leaf are always in a state of tension; and that it is +owing to this mechanical state, aided probably by fresh fluid being attracted +into the cells, that the lobes begin to separate or expand as soon as the +contraction of the upper surface diminishes. A leaf was cut off and suddenly +plunged perpendicularly into boiling water: I expected that the lobes would +have closed, but instead of doing so, they diverged a little. I then took +another fine leaf, with the lobes standing at an angle of nearly 80o to each +other; and on immersing it as before, the angle suddenly increased to 90o. A +third leaf was torpid from having recently re-expanded after having caught a +fly, so that repeated touches of the filaments caused not the least movement; +nevertheless, when similarly immersed, the lobes separated a little. As these +leaves were inserted perpendicularly into the boiling water, both surfaces and +the filaments [page 320] must have been equally affected; and I can understand +the divergence of the lobes only by supposing that the cells on the lower side, +owing to their state of tension, acted mechanically and thus suddenly drew the +lobes a little apart, as soon as the cells on the upper surface were killed and +lost their contractile power. We have seen that boiling water in like manner +causes the tentacles of Drosera to curve backwards; and this is an analogous +movement to the divergence of the lobes of Dionaea. +</p> + +<p> +In some concluding remarks in the fifteenth chapter on the Droseraceae, the +different kinds of irritability possessed by the several genera, and the +different manner in which they capture insects, will be compared. [page 321] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0014" id="link2HCH0014"></a> +CHAPTER XIV.<br/> +ALDROVANDA VESICULOSA.</h2> + +<p class="letter"> +Captures crustaceans—Structure of the leaves in comparison with those of +Dionaea— Absorption by the glands, by the quadrifid processes, and points +on the infolded margins— Aldrovanda vesiculosa, var. +australis—Captures prey—Absorption of animal +matter—Aldrovanda vesiculosa, var. verticillata—Concluding remarks. +</p> + +<p> +This plant may be called a miniature aquatic Dionaea. Stein discovered in 1873 +that the bilobed leaves, which are generally found closed in Europe, open under +a sufficiently high temperature, and, when touched, suddenly close.* They +re-expand in from 24 to 36 hours, but only, as it appears, when inorganic +objects are enclosed. The leaves sometimes contain bubbles of air, and were +formerly supposed to be bladders; hence the specific name of vesiculosa. Stein +observed that water-insects were sometimes caught, and Prof. Cohn has recently +found within the leaves of naturally growing plants many kinds of crustaceans +and larvæ.** Plants which had been kept in filtered water were placed by him in +a vessel con- +</p> + +<p class="footnote"> +* Since his original publication, Stein has found out that the irritability of +the leaves was observed by De Sassus, as recorded in ‘Bull. Bot. Soc. de +France,’ in 1861. Delpino states in a paper published in 1871 +(‘Nuovo Giornale Bot. Ital.’ vol. iii. p. 174) that “una +quantit di chioccioline e di altri animalcoli acquatici” are caught and +suffocated by the leaves. I presume that chioccioline are fresh-water molluscs. +It would be interesting to know whether their shells are at all corroded by the +acid of the digestive secretion. +</p> + +<p class="footnote"> +** I am greatly indebted to this distinguished naturalist for having sent me a +copy of his memoir on Aldrovanda, before its publication in his ‘Beiträge +zur Biologie der Pflanzen,’ drittes Heft, 1875, page 71. [page 322] +</p> + +<p> +taining numerous crustaceans of the genus Cypris, and next morning many were +found imprisoned and alive, still swimming about within the closed leaves, but +doomed to certain death. +</p> + +<p> +Directly after reading Prof. Cohn’s memoir, I received through the +kindness of Dr. Hooker living plants from Germany. As I can add nothing to +Prof. Cohn’s excellent description, I will give only two illustrations, +one of a whorl of leaves copied from his work, and the other of a leaf pressed +flat open, drawn by my son Francis. I will, however, append a few remarks on +the differences between this plant and Dionaea. +</p> + +<p> +Aldrovanda is destitute of roots and floats freely in the water. The leaves are +arranged in whorls round the stem. Their broad petioles terminate in from four +to six rigid projections,* each tipped with a stiff, short bristle. The bilobed +leaf, with the midrib likewise tipped with a bristle, stands in the midst of +these projections, and is evidently defended by them. The lobes are formed of +very delicate tissue, so as to be translucent; they open, according to Cohn, +about as much as the two valves of a living mussel-shell, therefore even less +than the lobes of Dionaea; and this must make the capture of aquatic animals +more easy. The outside of the leaves and the petioles are covered with minute +two-armed papillae, evidently answering to the eight-rayed papillae of Dionaea. +</p> + +<p> +Each lobe rather exceeds a semi-circle in convexity, and consists of two very +different concentric portions; the inner and lesser portion, or that next to +the midrib, +</p> + +<p class="footnote"> +* There has been much discussion by botanists on the homological nature of +these projections. Dr. Nitschke (‘Bot. Zeitung,’ 1861, p. 146) +believes that they correspond with the fimbriated scale-like bodies found at +the bases of the petioles of Drosera. [page 323] +</p> + +<p> +is slightly concave, and is formed, according to Cohn, of three layers of +cells. Its upper surface is studded with colourless glands like, but more +simple than, those of Dionaea; they are supported on distinct footstalks, +consisting of two rows of cells. The outer +</p> + +<p> +FIG. 13. (Aldrovanda vesiculosa.) Upper figure, whorl of leaves (from Prof. +Cohn). Lower figure, leaf pressed flat open and greatly enlarged. +</p> + +<p> +and broader portion of the lobe is flat and very thin, being formed of only two +layers of cells. Its upper surface does not bear any glands, but, in their +place, small quadrifid processes, each consisting of four tapering projections, +which rise from a common [page 324] prominence. These processes are formed of +very delicate membrane lined with a layer of protoplasm; and they sometimes +contain aggregated globules of hyaline matter. Two of the slightly diverging +arms are directed towards the circumference, and two towards the midrib, +forming together a sort of Greek cross. Occasionally two of the arms are +replaced by one, and then the projection is trifid. We shall see in a future +chapter that these projections curiously resemble those found within the +bladders of Utricularia, more especially of Utricularia montana, although this +genus is not related to Aldrovanda. +</p> + +<p> +A narrow rim of the broad flat exterior part of each lobe is turned inwards, so +that, when the lobes are closed, the exterior surfaces of the infolded portions +come into contact. The edge itself bears a row of conical, flattened, +transparent points with broad bases, like the prickles on the stem of a bramble +or Rubus. As the rim is infolded, these points are directed towards the midrib, +and they appear at first as if they were adapted to prevent the escape of prey; +but this can hardly be their chief function, for they are composed of very +delicate and highly flexible membrane, which can be easily bent or quite +doubled back without being cracked. Nevertheless, the infolded rims, together +with the points, must somewhat interfere with the retrograde movement of any +small creature, as soon as the lobes begin to close. The circumferential part +of the leaf of Aldrovanda thus differs greatly from that of Dionaea; nor can +the points on the rim be considered as homologous with the spikes round the +leaves of Dionaea, as these latter are prolongations of the blade, and not mere +epidermic productions. They appear also to serve for a widely different +purpose. [page 325] +</p> + +<p> +On the concave gland-bearing portion of the lobes, and especially on the +midrib, there are numerous, long, finely pointed hairs, which, as Prof. Cohn +remarks, there can be little doubt are sensitive to a touch, and, when touched, +cause the leaf to close. They are formed of two rows of cells, or, according to +Cohn, sometimes of four, and do not include any vascular tissue. They differ +also from the six sensitive filaments of Dionaea in being colourless, and in +having a medial as well as a basal articulation. No doubt it is owing to these +two articulations that, notwithstanding their length, they escape being broken +when the lobes close. +</p> + +<p> +The plants which I received during the early part of October from Kew never +opened their leaves, though subjected to a high temperature. After examining +the structure of some of them, I experimented on only two, as I hoped that the +plants would grow; and I now regret that I did not sacrifice a greater number. +</p> + +<p> +A leaf was cut open along the midrib, and the glands examined under a high +power. It was then placed in a few drops of an infusion of raw meat. After 3 +hrs. 20 m. there was no change, but when next examined after 23 hrs. 20 m., the +outer cells of the glands contained, instead of limpid fluid, spherical masses +of a granular substance, showing that matter had been absorbed from the +infusion. That these glands secrete a fluid which dissolves or digests animal +matter out of the bodies of the creatures which the leaves capture, is also +highly probable from the analogy of Dionaea. If we may trust to the same +analogy, the concave and inner portions of the two lobes probably close +together by a slow movement, as soon as the glands have absorbed a slight +amount of [page 326] already soluble animal matter. The included water would +thus be pressed out, and the secretion consequently not be too much diluted to +act. With respect to the quadrifid processes on the outer parts of the lobes, I +was not able to decide whether they had been acted on by the infusion; for the +lining of protoplasm was somewhat shrunk before they were immersed. Many of the +points on the infolded rims also had their lining of protoplasm similarly +shrunk, and contained spherical granules of hyaline matter. +</p> + +<p> +A solution of urea was next employed. This substance was chosen partly because +it is absorbed by the quadrifid processes and more especially by the glands of +Utricularia—a plant which, as we shall hereafter see, feeds on decayed +animal matter. As urea is one of the last products of the chemical changes +going on in the living body, it seems fitted to represent the early stages of +the decay of the dead body. I was also led to try urea from a curious little +fact mentioned by Prof. Cohn, namely that when rather large crustaceans are +caught between the closing lobes, they are pressed so hard whilst making their +escape that they often void their sausage-shaped masses of excrement, which +were found within most of the leaves. These masses, no doubt, contain urea. +They would be left either on the broad outer surfaces of the lobes where the +quadrifids are situated, or within the closed concavity. In the latter case, +water charged with excrementitious and decaying matter would be slowly forced +outwards, and would bathe the quadrifids, if I am right in believing that the +concave lobes contract after a time like those of Dionaea. Foul water would +also be apt to ooze out at all times, especially when bubbles of air were +generated within the concavity. +</p> + +<p> +A leaf was cut open and examined, and the outer [page 327] cells of the glands +were found to contain only limpid fluid. Some of the quadrifids included a few +spherical granules, but several were transparent and empty, and their positions +were marked. This leaf was now immersed in a little solution of one part of +urea to 146 of water, or three grains to the ounce. After 3 hrs. 40 m. there +was no change either in the glands or quadrifids; nor was there any certain +change in the glands after 24 hrs.; so that, as far as one trial goes, urea +does not act on them in the same manner as an infusion of raw meat. It was +different with the quadrifids; for the lining of protoplasm, instead of +presenting a uniform texture, was now slightly shrunk, and exhibited in many +places minute, thickened, irregular, yellowish specks and ridges, exactly like +those which appear within the quadrifids of Utricularia when treated with this +same solution. Moreover, several of the quadrifids, which were before empty, +now contained moderately sized or very small, more or less aggregated, globules +of yellowish matter, as likewise occurs under the same circumstances with +Utricularia. Some of the points on the infolded margins of the lobes were +similarly affected; for their lining of protoplasm was a little shrunk and +included yellowish specks; and those which were before empty now contained +small spheres and irregular masses of hyaline matter, more or less aggregated; +so that both the points on the margins and the quadrifids had absorbed matter +from the solution in the course of 24 hrs.; but to this subject I shall recur. +In another rather old leaf, to which nothing had been given, but which had been +kept in foul water, some of the quadrifids contained aggregated translucent +globules. These were not acted on by a solution of one part of carbonate of +ammonia to 218 of water; and this negative result [page 328] agrees with what I +have observed under similar circumstances with Utricularia. +</p> + +<p> +Aldrovanda vesiculosa, var. australis.—Dried leaves of this plant from +Queensland in Australia were sent me by Prof. Oliver from the herbarium at Kew. +Whether it ought to be considered as a distinct species or a variety, cannot be +told until the flowers are examined by a botanist. The projections at the upper +end of the petiole (from four to six in number) are considerably longer +relatively to the blade, and much more attenuated than those of the European +form. They are thickly covered for a considerable space near their extremities +with the upcurved prickles, which are quite absent in the latter form; and they +generally bear on their tips two or three straight prickles instead of one. The +bilobed leaf appears also to be rather larger and somewhat broader, with the +pedicel by which it is attached to the upper end of the petiole a little +longer. The points on the infolded margins likewise differ; they have narrower +bases, and are more pointed; long and short points also alternate with much +more regularity than in the European form. The glands and sensitive hairs are +similar in the two forms. No quadrifid processes could be seen on several of +the leaves, but I do not doubt that they were present, though indistinguishable +from their delicacy and from having shrivelled; for they were quite distinct on +one leaf under circumstances presently to be mentioned. +</p> + +<p> +Some of the closed leaves contained no prey, but in one there was a rather +large beetle, which from its flattened tibiae I suppose was an aquatic species, +but was not allied to Colymbetes. All the softer tissues of this beetle were +completely dissolved, and its chitinous integuments were as clean as if they +had been [page 329] boiled in caustic potash; so that it must have been +enclosed for a considerable time. The glands were browner and more opaque than +those on other leaves which had caught nothing; and the quadrifid processes, +from being partly filled with brown granular matter, could be plainly +distinguished, which was not the case, as already stated, on the other leaves. +Some of the points on the infolded margins likewise contained brownish granular +matter. We thus gain additional evidence that the glands, the quadrifid +processes, and the marginal points, all have the power of absorbing matter, +though probably of a different nature. +</p> + +<p> +Within another leaf disintegrated remnants of a rather small animal, not a +crustacean, which had simple, strong, opaque mandibles, and a large +unarticulated chitinous coat, were present. Lumps of black organic matter, +possibly of a vegetable nature, were enclosed in two other leaves; but in one +of these there was also a small worm much decayed. But the nature of partially +digested and decayed bodies, which have been pressed flat, long dried, and then +soaked in water, cannot be recognised easily. All the leaves contained +unicellular and other Algae, still of a greenish colour, which had evidently +lived as intruders, in the same manner as occurs, according to Cohn, within the +leaves of this plant in Germany. +</p> + +<p> +Aldrovanda vesiculosa, var. verticillata.—Dr. King, Superintendent of the +Botanic Gardens, kindly sent me dried specimens collected near Calcutta. This +form was, I believe, considered by Wallich as a distinct species, under the +name of verticillata. It resembles the Australian form much more nearly than +the European; namely in the projections at the upper end of the petiole being +much attenuated and covered with [page 330] upcurved prickles; they terminate +also in two straight little prickles. The bilobed leaves are, I believe, larger +and certainly broader even than those of the Australian form; so that the +greater convexity of their margins was conspicuous. The length of an open leaf +being taken at 100, the breadth of the Bengal form is nearly 173, of the +Australian form 147, and of the German 134. The points on the infolded margins +are like those in the Australian form. Of the few leaves which were examined, +three contained entomostracan crustaceans. +</p> + +<p> +Concluding Remarks.—The leaves of the three foregoing closely allied +species or varieties are manifestly adapted for catching living creatures. With +respect to the functions of the several parts, there can be little doubt that +the long jointed hairs are sensitive, like those of Dionaea, and that, when +touched, they cause the lobes to close. That the glands secrete a true +digestive fluid and afterwards absorb the digested matter, is highly probable +from the analogy of Dionaea,—from the limpid fluid within their cells +being aggregated into spherical masses, after they had absorbed an infusion of +raw meat,—from their opaque and granular condition in the leaf, which had +enclosed a beetle for a long time,—and from the clean condition of the +integuments of this insect, as well as of crustaceans (as described by Cohn), +which have been long captured. Again, from the effect produced on the quadrifid +processes by an immersion for 24 hrs. in a solution of urea,—from the +presence of brown granular matter within the quadrifids of the leaf in which +the beetle had been caught,—and from the analogy of Utricularia,—it +is probable that these processes absorb excrementitious and decaying animal +matter. It is a more curious fact that the points on [page 331] the infolded +margins apparently serve to absorb decayed animal matter in the same manner as +the quadrifids. We can thus understand the meaning of the infolded margins of +the lobes furnished with delicate points directed inwards, and of the broad, +flat, outer portions, bearing quadrifid processes; for these surfaces must be +liable to be irrigated by foul water flowing from the concavity of the leaf +when it contains dead animals. This would follow from various +causes,—from the gradual contraction of the concavity,—from fluid +in excess being secreted,—and from the generation of bubbles of air. More +observations are requisite on this head; but if this view is correct, we have +the remarkable case of different parts of the same leaf serving for very +different purposes—one part for true digestion, and another for the +absorption of decayed animal matter. We can thus also understand how, by the +gradual loss of either power, a plant might be gradually adapted for the one +function to the exclusion of the other; and it will hereafter be shown that two +genera, namely Pinguicula and Utricularia, belonging to the same family, have +been adapted for these two different functions. [page 332] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0015" id="link2HCH0015"></a> +CHAPTER XV.<br/> +DROSOPHYLLUM—RORIDULA—BYBLIS—GLANDULAR HAIRS OF OTHER +PLANTS—CONCLUDING REMARKS ON THE DROSERACEÆ.</h2> + +<p class="letter"> +Drosophyllum—Structure of leaves—Nature of the +secretion—Manner of catching insects— Power of +absorption—Digestion of animal substances—Summary on +Drosophyllum—Roridula—Byblis—Glandular hairs of other plants, +their power of absorption—Saxifraga—Primula— +Pelargonium—Erica—Mirabilis—Nicotiana—Summary on +glandular hairs—Concluding remarks on the Droseraceae. +</p> + +<p> +Drosophyllum lusitanicum.—This rare plant has been found only in +Portugal, and, as I hear from Dr. Hooker, in Morocco. I obtained living +specimens through the great kindness of Mr. W.C. Tait, and afterwards from Mr. +G. Maw and Dr. Moore. Mr. Tait informs me that it grows plentifully on the +sides of dry hills near Oporto, and that vast numbers of flies adhere to the +leaves. This latter fact is well-known to the villagers, who call the plant the +“fly-catcher,” and hang it up in their cottages for this purpose. A +plant in my hot-house caught so many insects during the early part of April, +although the weather was cold and insects scarce, that it must have been in +some manner strongly attractive to them. On four leaves of a young and small +plant, 8, 10, 14, and 16 minute insects, chiefly Diptera, were found in the +autumn adhering to them. I neglected to examine the roots, but I hear from Dr. +Hooker that they are very small, as in the case of the previously mentioned +members of the same family of the Droseraceae. +</p> + +<p> +The leaves arise from an almost woody axis; they [page 333] are linear, much +attenuated towards their tips, and several inches in length. The upper surface +is concave, the lower convex, with a narrow channel down the middle. Both +surfaces, with the exception of the channel, are covered with glands, supported +on pedicels and arranged in irregular longitudinal rows. These organs I shall +call tentacles, from their close resemblance to those of Drosera, though they +have no power of movement. Those on the same leaf differ much in length. The +glands also differ in size, and are of a bright pink or of a purple colour; +their upper surfaces are convex, and the lower flat or even concave, so that +they resemble miniature mushrooms in appearance. They are formed of two (as I +believe) layers of delicate angular cells, enclosing eight or ten larger cells +with thicker, zigzag walls. Within these larger cells there are others marked +by spiral lines, and apparently connected with the spiral vessels which run up +the green multi-cellular pedicels. The glands secrete large drops of viscid +secretion. Other glands, having the same general appearance, are found on the +flower-peduncles and calyx. +</p> + +<p> +FIG. 14. (Drosophyllum lusitanicum.) Part of leaf, enlarged seven times, +showing lower surface. +</p> + +<p> +Besides the glands which are borne on longer or shorter pedicels, there are +numerous ones, both on the upper and lower surfaces of the leaves, so small as +to be scarcely visible to the naked eye. They are colourless and almost +sessile, either circular or oval in outline; the latter occurring chiefly on +the backs of the leaves (fig. 14). Internally they have exactly the same +structure as the larger glands which are supported on pedicels; [page 334] and +indeed the two sets almost graduate into one another. But the sessile glands +differ in one important respect, for they never secrete spontaneously, as far +as I have seen, though I have examined them under a high power on a hot day, +whilst the glands on pedicels were secreting copiously. Nevertheless, if little +bits of damp albumen or fibrin are placed on these sessile glands, they begin +after a time to secrete, in the same manner as do the glands of Dionaea when +similarly treated. When they were merely rubbed with a bit of raw meat, I +believe that they likewise secreted. Both the sessile glands and the taller +ones on pedicels have the power of rapidly absorbing nitrogenous matter. +</p> + +<p> +The secretion from the taller glands differs in a remarkable manner from that +of Drosera, in being acid before the glands have been in any way excited; and +judging from the changed colour of litmus paper, more strongly acid than that +of Drosera. This fact was observed repeatedly; on one occasion I chose a young +leaf, which was not secreting freely, and had never caught an insect, yet the +secretion on all the glands coloured litmus paper of a bright red. From the +quickness with which the glands are able to obtain animal matter from such +substances as well-washed fibrin and cartilage, I suspect that a small quantity +of the proper ferment must be present in the secretion before the glands are +excited, so that a little animal matter is quickly dissolved. +</p> + +<p> +Owing to the nature of the secretion or to the shape of the glands, the drops +are removed from them with singular facility. It is even somewhat difficult, by +the aid of a finely pointed polished needle, slightly damped with water, to +place a minute particle of any kind on one of the drops; for on withdrawing the +[page 335] needle, the drop is generally withdrawn; whereas with Drosera there +is no such difficulty, though the drops are occasionally withdrawn. From this +peculiarity, when a small insect alights on a leaf of Drosophyllum, the drops +adhere to its wings, feet, or body, and are drawn from the gland; the insect +then crawls onward and other drops adhere to it; so that at last, bathed by the +viscid secretion, it sinks down and dies, resting on the small sessile glands +with which the surface of the leaf is thickly covered. In the case of Drosera, +an insect sticking to one or more of the exterior glands is carried by their +movement to the centre of the leaf; with Drosophyllum, this is effected by the +crawling of the insect, as from its wings being clogged by the secretion it +cannot fly away. +</p> + +<p> +There is another difference in function between the glands of these two plants: +we know that the glands of Drosera secrete more copiously when properly +excited. But when minute particles of carbonate of ammonia, drops of a solution +of this salt or of the nitrate of ammonia, saliva, small insects, bits of raw +or roast meat, albumen, fibrin or cartilage, as well as inorganic particles, +were placed on the glands of Drosophyllum, the amount of secretion never +appeared to be in the least increased. As insects do not commonly adhere to the +taller glands, but withdraw the secretion, we can see that there would be +little use in their having acquired the habit of secreting copiously when +stimulated; whereas with Drosera this is of use, and the habit has been +acquired. Nevertheless, the glands of Drosophyllum, without being stimulated, +continually secrete, so as to replace the loss by evaporation. Thus when a +plant was placed under a small bell-glass with its inner surface and support +thoroughly wetted, there was no loss by evaporation, and so much [page 336] +secretion was accumulated in the course of a day that it ran down the tentacles +and covered large spaces of the leaves. +</p> + +<p> +The glands to which the above named nitrogenous substances and liquids were +given did not, as just stated, secrete more copiously; on the contrary, they +absorbed their own drops of secretion with surprising quickness. Bits of damp +fibrin were placed on five glands, and when they were looked at after an +interval of 1 hr. 12 m., the fibrin was almost dry, the secretion having been +all absorbed. So it was with three cubes of albumen after 1 hr. 19 m., and with +four other cubes, though these latter were not looked at until 2 hrs. 15 m. had +elapsed. The same result followed in between 1 hr. 15 m. and 1 hr. 30 m. when +particles both of cartilage and meat were placed on several glands. Lastly, a +minute drop (about 1/20 of a minim) of a solution of one part of nitrate of +ammonia to 146 of water was distributed between the secretion surrounding three +glands, so that the amount of fluid surrounding each was slightly increased; +yet when looked at after 2 hrs., all three were dry. On the other hand, seven +particles of glass and three of coal-cinders, of nearly the same size as those +of the above named organic substances, were placed on ten glands; some of them +being observed for 18 hrs., and others for two or three days; but there was not +the least sign of the secretion being absorbed. Hence, in the former cases, the +absorption of the secretion must have been due to the presence of some +nitrogenous matter, which was either already soluble or was rendered so by the +secretion. As the fibrin was pure, and had been well washed in distilled water +after being kept in glycerine, and as the cartilage had been soaked in water, I +suspect that these substances must [page 337] have been slightly acted on and +rendered soluble within the above stated short periods. +</p> + +<p> +The glands have not only the power of rapid absorption, but likewise of +secreting again quickly; and this latter habit has perhaps been gained, +inasmuch as insects, if they touch the glands, generally withdraw the drops of +secretion, which have to be restored. The exact period of re-secretion was +recorded in only a few cases. The glands on which bits of meat were placed, and +which were nearly dry after about 1 hr. 30 m., when looked at after 22 +additional hours, were found secreting; so it was after 24 hrs. with one gland +on which a bit of albumen had been placed. The three glands to which a minute +drop of a solution of nitrate of ammonia was distributed, and which became dry +after 2 hrs., were beginning to re-secrete after only 12 additional hours. +</p> + +<p> +Tentacles Incapable of Movement.—Many of the tall tentacles, with insects +adhering to them, were carefully observed; and fragments of insects, bits of +raw meat, albumen, &c., drops of a solution of two salts of ammonia and of +saliva, were placed on the glands of many tentacles; but not a trace of +movement could ever be detected. I also repeatedly irritated the glands with a +needle, and scratched and pricked the blades, but neither the blade nor the +tentacles became at all inflected. We may therefore conclude that they are +incapable of movement. +</p> + +<p> +On the Power of Absorption possessed by the Glands.—It has already been +indirectly shown that the glands on pedicels absorb animal matter; and this is +further shown by their changed colour, and by the aggregation of their +contents, after they have been left in contact with nitrogenous substances or +liquids. The following observations apply both to the glands supported on [page +338] pedicels and to the minute sessile ones. Before a gland has been in any +way stimulated, the exterior cells commonly contain only limpid purple fluid; +the more central ones including mulberry-like masses of purple granular matter. +A leaf was placed in a little solution of one part of carbonate of ammonia to +146 of water (3 grs. to 1 oz.), and the glands were instantly darkened and very +soon became black; this change being due to the strongly marked aggregation of +their contents, more especially of the inner cells. Another leaf was placed in +a solution of the same strength of nitrate of ammonia, and the glands were +slightly darkened in 25 m., more so in 50 m., and after 1 hr. 30 m. were of so +dark a red as to appear almost black. Other leaves were placed in a weak +infusion of raw meat and in human saliva, and the glands were much darkened in +25 m., and after 40 m. were so dark as almost to deserve to be called black. +Even immersion for a whole day in distilled water occasionally induces some +aggregation within the glands, so that they become of a darker tint. In all +these cases the glands are affected in exactly the same manner as those of +Drosera. Milk, however, which acts so energetically on Drosera, seems rather +less effective on Drosophyllum, for the glands were only slightly darkened by +an immersion of 1 hr. 20 m., but became decidedly darker after 3 hrs. Leaves +which had been left for 7 hrs. in an infusion of raw meat or in saliva were +placed in the solution of carbonate of ammonia, and the glands now became +greenish; whereas, if they had been first placed in the carbonate, they would +have become black. In this latter case, the ammonia probably combines with the +acid of the secretion, and therefore does not act on the colouring matter; but +when the glands are first subjected to an organic [page 339] fluid, either the +acid is consumed in the work of digestion or the cell-walls are rendered more +permeable, so that the undecomposed carbonate enters and acts on the colouring +matter. If a particle of the dry carbonate is placed on a gland, the purple +colour is quickly discharged, owing probably to an excess of the salt. The +gland, moreover, is killed. +</p> + +<p> +Turning now to the action of organic substances, the glands on which bits of +raw meat were placed became dark-coloured; and in 18 hrs. their contents were +conspicuously aggregated. Several glands with bits of albumen and fibrin were +darkened in between 2 hrs. and 3 hrs.; but in one case the purple colour was +completely discharged. Some glands which had caught flies were compared with +others close by; and though they did not differ much in colour, there was a +marked difference in their state of aggregation. In some few instances, +however, there was no such difference, and this appeared to be due to the +insects having been caught long ago, so that the glands had recovered their +pristine state. In one case, a group of the sessile colourless glands, to which +a small fly adhered, presented a peculiar appearance; for they had become +purple, owing to purple granular matter coating the cell-walls. I may here +mention as a caution that, soon after some of my plants arrived in the spring +from Portugal, the glands were not plainly acted on by bits of meat, or +insects, or a solution of ammonia—a circumstance for which I cannot +account. +</p> + +<p> +Digestion of Solid Animal Matter.—Whilst I was trying to place on two of +the taller glands little cubes of albumen, these slipped down, and, besmeared +with secretion, were left resting on some of the small sessile glands. After 24 +hrs. one of these cubes was found [page 340] completely liquefied, but with a +few white streaks still visible; the other was much rounded, but not quite +dissolved. Two other cubes were left on tall glands for 2 hrs. 45 m., by which +time all the secretion was absorbed; but they were not perceptibly acted on, +though no doubt some slight amount of animal matter had been absorbed from +them. They were then placed on the small sessile glands, which being thus +stimulated secreted copiously in the course of 7 hrs. One of these cubes was +much liquefied within this short time; and both were completely liquefied after +21 hrs. 15 m.; the little liquid masses, however, still showing some white +streaks. These streaks disappeared after an additional period of 6 hrs. 30 m.; +and by next morning (i.e. 48 hrs. from the time when the cubes were first +placed on the glands) the liquefied matter was wholly absorbed. A cube of +albumen was left on another tall gland, which first absorbed the secretion and +after 24 hrs. poured forth a fresh supply. This cube, now surrounded by +secretion, was left on the gland for an additional 24 hrs., but was very +little, if at all, acted on. We may, therefore, conclude, either that the +secretion from the tall glands has little power of digestion, though strongly +acid, or that the amount poured forth from a single gland is insufficient to +dissolve a particle of albumen which within the same time would have been +dissolved by the secretion from several of the small sessile glands. Owing to +the death of my last plant, I was unable to ascertain which of these +alternatives is the true one. +</p> + +<p> +Four minute shreds of pure fibrin were placed, each resting on one, two, or +three of the taller glands. In the course of 2 hrs. 30 m. the secretion was all +absorbed, and the shreds were left almost dry. They [page 341] were then pushed +on to the sessile glands. One shred, after 2 hrs. 30 m., seemed quite +dissolved, but this may have been a mistake. A second, when examined after 17 +hrs. 25 m., was liquefied, but the liquid as seen under the microscope still +contained floating granules of fibrin. The other two shreds were completely +liquefied after 21 hrs. 30 m.; but in one of the drops a very few granules +could still be detected. These, however, were dissolved after an additional +interval of 6 hrs. 30 m.; and the surface of the leaf for some distance all +round was covered with limpid fluid. It thus appears that Drosophyllum digests +albumen and fibrin rather more quickly than Drosera can; and this may perhaps +be attributed to the acid, together probably with some small amount of the +ferment, being present in the secretion, before the glands have been +stimulated; so that digestion begins at once. +</p> + +<p> +Concluding Remarks.—The linear leaves of Drosophyllum differ but slightly +from those of certain species of Drosera; the chief differences being, firstly, +the presence of minute, almost sessile, glands, which, like those of Dionaea, +do not secrete until they are excited by the absorption of nitrogenous matter. +But glands of this kind are present on the leaves of Drosera binata, and appear +to be represented by the papillae on the leaves of Drosera rotundifolia. +Secondly, the presence of tentacles on the backs of the leaves; but we have +seen that a few tentacles, irregularly placed and tending towards abortion, are +retained on the backs of the leaves of Drosera binata. There are greater +differences in function between the two genera. The most important one is that +the tentacles of Drosophyllum have no power of movement; this loss being +partially replaced by the drops of viscid [page 342] secretion being readily +withdrawn from the glands; so that, when an insect comes into contact with a +drop, it is able to crawl away, but soon touches other drops, and then, +smothered by the secretion, sinks down on the sessile glands and dies. Another +difference is, that the secretion from the tall glands, before they have been +in any way excited, is strongly acid, and perhaps contains a small quantity of +the proper ferment. Again, these glands do not secrete more copiously from +being excited by the absorption of nitrogenous matter; on the contrary, they +then absorb their own secretion with extraordinary quickness. In a short time +they begin to secrete again. All these circumstances are probably connected +with the fact that insects do not commonly adhere to the glands with which they +first come into contact, though this does sometimes occur; and that it is +chiefly the secretion from the sessile glands which dissolves animal matter out +of their bodies. +</p> + +<p class="center"> +R<small>ORIDULA</small>. +</p> + +<p> +Roridula dentata.—This plant, a native of the western parts of the Cape +of Good Hope, was sent to me in a dried state from Kew. It has an almost woody +stem and branches, and apparently grows to a height of some feet. The leaves +are linear, with their summits much attenuated. Their upper and lower surfaces +are concave, with a ridge in the middle, and both are covered with tentacles, +which differ greatly in length; some being very long, especially those on the +tips of the leaves, and some very short. The glands also differ much in size +and are somewhat elongated. They are supported on multicellular pedicels. +</p> + +<p> +This plant, therefore, agrees in several respects with [page 343] Drosophyllum, +but differs in the following points. I could detect no sessile glands; nor +would these have been of any use, as the upper surface of the leaves is thickly +clothed with pointed, unicellular hairs directed upwards. The pedicels of the +tentacles do not include spiral vessels; nor are there any spiral cells within +the glands. The leaves often arise in tufts and are pinnatifid, the divisions +projecting at right angles to the main linear blade. These lateral divisions +are often very short and bear only a single terminal tentacle, with one or two +short ones on the sides. No distinct line of demarcation can be drawn between +the pedicels of the long terminal tentacles and the much attenuated summits of +the leaves. We may, indeed, arbitrarily fix on the point to which the spiral +vessels proceeding from the blade extend; but there is no other distinction. +</p> + +<p> +It was evident from the many particles of dirt sticking to the glands that they +secrete much viscid matter. A large number of insects of many kinds also +adhered to the leaves. I could nowhere discover any signs of the tentacles +having been inflected over the captured insects; and this probably would have +been seen even in the dried specimens, had they possessed the power of +movement. Hence, in this negative character, Roridula resembles its northern +representative, Drosophyllum. +</p> + +<p class="center"> +B<small>YBLIS</small>. +</p> + +<p> +Byblis gigantea (Western Australia).—A dried specimen, about 18 inches in +height, with a strong stem, was sent me from Kew. The leaves are some inches in +length, linear, slightly flattened, with a small projecting rib on the lower +surface. They are covered on all sides by glands of two kinds [page 344] +—sessile ones arranged in rows, and others supported on moderately long +pedicels. Towards the narrow summits of the leaves the pedicels are longer than +elsewhere, and here equal the diameter of the leaf. The glands are purplish, +much flattened, and formed of a single layer of radiating cells, which in the +larger glands are from forty to fifty in number. The pedicels consist of single +elongated cells, with colourless, extremely delicate walls, marked with the +finest intersecting spiral lines. Whether these lines are the result of +contraction from the drying of the walls, I do not know, but the whole pedicel +was often spirally rolled up. These glandular hairs are far more simple in +structure than the so-called tentacles of the preceding genera, and they do not +differ essentially from those borne by innumerable other plants. The +flower-peduncles bear similar glands. The most singular character about the +leaves is that the apex is enlarged into a little knob, covered with glands, +and about a third broader than the adjoining part of the attenuated leaf. In +two places dead flies adhered to the glands. As no instance is known of +unicellular structures having any power of movement,* Byblis, no doubt, catches +insects solely by the aid of its viscid secretion. These probably sink down +besmeared with the secretion and rest on the small sessile glands, which, if we +may judge by the analogy of Drosophyllum, then pour forth their secretion and +afterwards absorb the digested matter. +</p> + +<p> +Supplementary Observations on the Power of Absorption by the Glandular Hairs of +other Plants.—A few observations on this subject may be here conveniently +introduced. As the glands of many, probably of all, +</p> + +<p class="footnote"> +* Sachs, ‘Traité de Bot.,’ 3rd edit. 1874, p. 1026. [page 345] +</p> + +<p> +the species of Droseraceae absorb fluids or at least allow them readily to +enter,* it seemed desirable to ascertain how far the glands of other plants +which are not specially adapted for capturing insects, had the same power. +Plants were chosen for trial at hazard, with the exception of two species of +saxifrage, which were selected from belonging to a family allied to the +Droseraceae. Most of the experiments were made by immersing the glands either +in an infusion of raw meat or more commonly in a solution of carbonate of +ammonia, as this latter substance acts so powerfully and rapidly on protoplasm. +It seemed also particularly desirable to ascertain whether ammonia was +absorbed, as a small amount is contained in rain-water. With the Droseraceae +the secretion of a viscid fluid by the glands does not prevent their absorbing; +so that the glands of other plants might excrete superfluous matter, or secrete +an odoriferous fluid as a protection against the attacks of insects, or for any +other purpose, and yet have the power of absorbing. I regret that in the +following cases I did not try whether the secretion could digest or render +soluble animal substances, but such experiments would have been difficult on +account of the small size of the glands and the small amount of secretion. We +shall see in the next chapter that the secretion from the glandular hairs of +Pinguicula certainly dissolves animal matter. +</p> + +<p> +[Saxifraga umbrosa.—The flower-peduncles and petioles of the leaves are +clothed with short hairs, bearing pink-coloured glands, formed of several +polygonal cells, with their pedicels divided by partitions into distinct cells, +which are generally colourless, but sometimes pink. The glands secrete a +yellowish viscid fluid, by +</p> + +<p class="footnote"> +* The distinction between true absorption and mere permeation, or imbibition, +is by no means clearly understood: see Müller’s ‘Physiology,’ +Eng. translat. 1838, vol. i. p. 280. [page 346] +</p> + +<p> +which minute Diptera are sometimes, though not often, caught.* The cells of the +glands contain bright pink fluid, charged with granules or with globular masses +of pinkish pulpy matter. This matter must be protoplasm, for it is seen to +undergo slow but incessant changes of form if a gland be placed in a drop of +water and examined. Similar movements were observed after glands had been +immersed in water for 1, 3, 5, 18, and 27 hrs. Even after this latter period +the glands retained their bright pink colour; and the protoplasm within their +cells did not appear to have become more aggregated. The continually changing +forms of the little masses of protoplasm are not due to the absorption of +water, as they were seen in glands kept dry. +</p> + +<p> +A flower-stem, still attached to a plant, was bent (May 29) so as to remain +immersed for 23 hrs. 30 m. in a strong infusion of raw meat. The colour of the +contents of the glands was slightly changed, being now of a duller and more +purple tint than before. The contents also appeared more aggregated, for the +spaces between the little masses of protoplasm were wider; but this latter +result did not follow in some other and similar experiments. The masses seemed +to change their forms more rapidly than did those in water; so that the cells +had a different appearance every four or five minutes. Elongated masses became +in the course of one or two minutes spherical; and spherical ones drew +themselves out and united with others. Minute masses rapidly increased in size, +and three distinct ones were seen to unite. The movements were, in short, +exactly like those described in the case of Drosera. The cells of the pedicels +were not affected by the infusion; nor were they in the following experiment. +</p> + +<p> +Another flower-stem was placed in the same manner and for the same length of +time in a solution of one part of nitrate of ammonia to 146 of water (or 3 grs. +to 1 oz.), and the glands were discoloured in exactly the same manner as by the +infusion of raw meat. +</p> + +<p> +Another flower-stem was immersed, as before, in a solution of one part of +carbonate of ammonia to 109 of water. The glands, after 1 hr. 30 m., were not +discoloured, but after 3 hrs. 45 m. most of them had become dull purple, some +of them blackish- +</p> + +<p class="footnote"> +* In the case of Saxifraga tridactylites, Mr. Druce says (‘Pharmaceutical +Journal,’ May 1875) that he examined some dozens of plants, and in almost +every instance remnants of insects adhered to the leaves. So it is, as I hear +from a friend, with this plant in Ireland. [page 347] +</p> + +<p> +green, a few being still unaffected. The little masses of protoplasm within the +cells were seen in movement. The cells of the pedicels were unaltered. The +experiment was repeated, and a fresh flower-stem was left for 23 hrs. in the +solution, and now a great effect was produced; all the glands were much +blackened, and the previously transparent fluid in the cells of the pedicels, +even down to their bases, contained spherical masses of granular matter. By +comparing many different hairs, it was evident that the glands first absorb the +carbonate, and that the effect thus produced travels down the hairs from cell +to cell. The first change which could be observed is a cloudy appearance in the +fluid, due to the formation of very fine granules, which afterwards aggregate +into larger masses. Altogether, in the darkening of the glands, and in the +process of aggregation travelling down the cells of the pedicels, there is the +closest resemblance to what takes place when a tentacle of Drosera is immersed +in a weak solution of the same salt. The glands, however, absorb very much more +slowly than those of Drosera. Besides the glandular hairs, there are +star-shaped organs which do not appear to secrete, and which were not in the +least affected by the above solutions. +</p> + +<p> +Although in the case of uninjured flower-stems and leaves the carbonate seems +to be absorbed only by the glands, yet it enters a cut surface much more +quickly than a gland. Strips of the rind of a flower-stem were torn off, and +the cells of the pedicels were seen to contain only colourless transparent +fluid; those of the glands including as usual some granular matter. These +strips were then immersed in the same solution as before (one part of the +carbonate to 109 of water), and in a few minutes granular matter appeared in +the lowercells of all the pedicels. The action invariably commenced (for I +tried the experiment repeatedly) in the lowest cells, and therefore close to +the torn surface, and then gradually travelled up the hairs until it reached +the glands, in a reversed direction to what occurs in uninjured specimens. The +glands then became discoloured, and the previously contained granular matter +was aggregated into larger masses. Two short bits of a flower-stem were also +left for 2 hrs. 40 m. in a weaker solution of one part of the carbonate to 218 +of water; and in both specimens the pedicels of the hairs near the cut ends now +contained much granular matter; and the glands were completely discoloured. +</p> + +<p> +Lastly, bits of meat were placed on some glands; these were examined after 23 +hrs., as were others, which had apparently not long before caught minute flies; +but they did not present any [page 348] difference from the glands of other +hairs. Perhaps there may not have been time enough for absorption. I think so +as some glands, on which dead flies had evidently long lain, were of a pale +dirty purple colour or even almost colourless, and the granular matter within +them presented an unusual and somewhat peculiar appearance. That these glands +had absorbed animal matter from the flies, probably by exosmose into the viscid +secretion, we may infer, not only from their changed colour, but because, when +placed in a solution of carbonate of ammonia, some of the cells in their +pedicels become filled with granular matter; whereas the cells of other hairs, +which had not caught flies, after being treated with the same solution for the +same length of time, contained only a small quantity of granular matter. But +more evidence is necessary before we fully admit that the glands of this +saxifrage can absorb, even with ample time allowed, animal matter from the +minute insects which they occasionally and accidentally capture. +</p> + +<p> +Saxifraga rotundifolia (?).—The hairs on the flower-stems of this species +are longer than those just described, and bear pale brown glands. Many were +examined, and the cells of the pedicels were quite transparent. A bent stem was +immersed for 30 m. in a solution of one part of carbonate of ammonia to 109 of +water, and two or three of the uppermost cells in the pedicels now contained +granular or aggregated matter; the glands having become of a bright +yellowish-green. The glands of this species therefore absorb the carbonate much +more quickly than do those of Saxifraga umbrosa, and the upper cells of the +pedicels are likewise affected much more quickly. Pieces of the stem were cut +off and immersed in the same solution; and now the process of aggregation +travelled up the hairs in a reversed direction; the cells close to the cut +surfaces being first affected. +</p> + +<p> +Primula sinensis.—The flower-stems, the upper and lower surfaces of the +leaves and their footstalks, are all clothed with a multitude of longer and +shorter hairs. The pedicels of the longer hairs are divided by transverse +partitions into eight or nine cells. The enlarged terminal cell is globular, +forming a gland which secretes a variable amount of thick, slightly viscid, not +acid, brownish-yellow matter. +</p> + +<p> +A piece of a young flower-stem was first immersed in distilled water for 2 hrs. +30 m., and the glandular hairs were not at all affected. Another piece, bearing +twenty-five short and nine long hairs, was carefully examined. The glands of +the latter contained no solid or semi-solid matter; and those of only two [page +349] of the twenty-five short hairs contained some globules. This piece was +then immersed for 2 hrs. in a solution of one part of carbonate of ammonia to +109 of water, and now the glands of the twenty-five shorter hairs, with two or +three exceptions, contained either one large or from two to five smaller +spherical masses of semi-solid matter. Three of the glands of the nine long +hairs likewise included similar masses. In a few hairs there were also globules +in the cells immediately beneath the glands. Looking to all thirty-four hairs, +there could be no doubt that the glands had absorbed some of the carbonate. +Another piece was left for only 1 hr. in the same solution, and aggregated +matter appeared in all the glands. My son Francis examined some glands of the +longer hairs, which contained little masses of matter, before they were +immersed in any solution; and these masses slowly changed their forms, so that +no doubt they consisted of protoplasm. He then irrigated these hairs for 1 hr. +15 m., whilst under the microscope, with a solution of one part of the +carbonate to 218 of water; the glands were not perceptibly affected, nor could +this have been expected, as their contents were already aggregated. But in the +cells of the pedicels numerous, almost colourless, spheres of matter appeared, +which changed their forms and slowly coalesced; the appearance of the cells +being thus totally changed at successive intervals of time. +</p> + +<p> +The glands on a young flower-stem, after having been left for 2 hrs. 45 m. in a +strong solution of one part of the carbonate to 109 of water, contained an +abundance of aggregated masses, but whether generated by the action of the +salt, I do not know. This piece was again placed in the solution, so that it +was immersed altogether for 6 hrs. 15 m., and now there was a great change; for +almost all the spherical masses within the gland-cells had disappeared, being +replaced by granular matter of a darker brown. The experiment was thrice +repeated with nearly the same result. On one occasion the piece was left +immersed for 8 hrs. 30 m., and though almost all the spherical masses were +changed into the brown granular matter, a few still remained. If the spherical +masses of aggregated matter had been originally produced merely by some +chemical or physical action, it seems strange that a somewhat longer immersion +in the same solution should so completely alter their character. But as the +masses which slowly and spontaneously changed their forms must have consisted +of living protoplasm, there is nothing surprising in its being injured or +killed, and its appearance wholly changed by long immersion in so strong a +solution of the carbonate as that [page 350] employed. A solution of this +strength paralyses all movement in Drosera, but does not kill the protoplasm; a +still stronger solution prevents the protoplasm from aggregating into the +ordinary full-sized globular masses, and these, though they do not +disintegrate, become granular and opaque. In nearly the same manner, too hot +water and certain solutions (for instance, of the salts of soda and potash) +cause at first an imperfect kind of aggregation in the cells of Drosera; the +little masses afterwards breaking up into granular or pulpy brown matter. All +the foregoing experiments were made on flower-stems, but a piece of a leaf was +immersed for 30 m. in a strong solution of the carbonate (one part to 109 of +water), and little globular masses of matter appeared in all the glands, which +before contained only limpid fluid. +</p> + +<p> +I made also several experiments on the action of the vapour of the carbonate on +the glands; but will give only a few cases. The cut end of the footstalk of a +young leaf was protected with sealing-wax, and was then placed under a small +bell-glass, with a large pinch of the carbonate. After 10 m. the glands showed +a considerable degree of aggregation, and the protoplasm lining the cells of +the pedicels was a little separated from the walls. Another leaf was left for +50 m. with the same result, excepting that the hairs became throughout their +whole length of a brownish colour. In a third leaf, which was exposed for 1 hr. +50 m., there was much aggregated matter in the glands; and some of the masses +showed signs of breaking up into brown granular matter. This leaf was again +placed in the vapour, so that it was exposed altogether for 5 hrs. 30 m.; and +now, though I examined a large number of glands, aggregated masses were found +in only two or three; in all the others, the masses, which before had been +globular, were converted into brown, opaque, granular matter. We thus see that +exposure to the vapour for a considerable time produces the same effects as +long immersion in a strong solution. In both cases there could hardly be a +doubt that the salt had been absorbed chiefly or exclusively by the glands. +</p> + +<p> +On another occasion bits of damp fibrin, drops of a weak infusion of raw meat +and of water, were left for 24 hrs. on some leaves; the hairs were then +examined, but to my surprise differed in no respect from others which had not +been touched by these fluids. Most of the cells, however, included hyaline, +motionless little spheres, which did not seem to consist of protoplasm, but, I +suppose, of some balsam or essential oil. +</p> + +<p> +Pelargonium zonale (var. edged with white).—The leaves [page 351] are +clothed with numerous multicellular hairs; some simply pointed; others bearing +glandular heads, and differing much in length. The glands on a piece of leaf +were examined and found to contain only limpid fluid; most of the water was +removed from beneath the covering glass, and a minute drop of one part of +carbonate of ammonia to 146 of water was added; so that an extremely small dose +was given. After an interval of only 3 m. there were signs of aggregation +within the glands of the shorter hairs; and after 5 m. many small globules of a +pale brown tint appeared in all of them; similar globules, but larger, being +found in the large glands of the longer hairs. After the specimen had been left +for 1 hr. in the solution, many of the smaller globules had changed their +positions; and two or three vacuoles or small spheres (for I know not which +they were) of a rather darker tint appeared within some of the larger globules. +Little globules could now be seen in some of the uppermost cells of the +pedicels, and the protoplasmic lining was slightly separated from the walls of +the lower cells. After 2 hrs. 30 m. from the time of first immersion, the large +globules within the glands of the longer hairs were converted into masses of +darker brown granular matter. Hence from what we have seen with Primula +sinensis, there can be little doubt that these masses originally consisted of +living protoplasm. +</p> + +<p> +A drop of a weak infusion of raw meat was placed on a leaf, and after 2 hrs. 30 +m. many spheres could be seen within the glands. These spheres, when looked at +again after 30 m., had slightly changed their positions and forms, and one had +separated into two; but the changes were not quite like those which the +protoplasm of Drosera undergoes. These hairs, moreover, had not been examined +before immersion, and there were similar spheres in some glands which had not +been touched by the infusion. +</p> + +<p> +Erica tetralix.—A few long glandular hairs project from the margins of +the upper surfaces of the leaves. The pedicels are formed of several rows of +cells, and support rather large globular heads, secreting viscid matter, by +which minute insects are occasionally, though rarely, caught. Some leaves were +left for 23 hrs. in a weak infusion of raw meat and in water, and the hairs +were then compared, but they differed very little or not at all. In both cases +the contents of the cells seemed rather more granular than they were before; +but the granules did not exhibit any movement. Other leaves were left for 23 +hrs. in a solution of one part of carbonate of ammonia to 218 of water, and +here again the granular matter appeared to have increased [page 352] in amount; +but one such mass retained exactly the same form as before after an interval of +5 hrs., so that it could hardly have consisted of living protoplasm. These +glands seem to have very little or no power of absorption, certainly much less +than those of the foregoing plants. +</p> + +<p> +Mirabilis longiflora.—The stems and both surfaces of the leaves bear +viscid hairs. young plants, from 12 to 18 inches in height in my greenhouse, +caught so many minute Diptera, Coleoptera, and larvæ, that they were quite +dusted with them. The hairs are short, of unequal lengths, formed of a single +row of cells, surmounted by an enlarged cell which secretes viscid matter. +These terminal cells or glands contain granules and often globules of granular +matter. Within a gland which had caught a small insect, one such mass was +observed to undergo incessant changes of form, with the occasional appearance +of vacuoles. But I do not believe that this protoplasm had been generated by +matter absorbed from the dead insect; for, on comparing several glands which +had and had not caught insects, not a shade of difference could be perceived +between them, and they all contained fine granular matter. A piece of leaf was +immersed for 24 hrs. in a solution of one part of carbonate of ammonia to 218 +of water, but the hairs seemed very little affected by it, excepting that +perhaps the glands were rendered rather more opaque. In the leaf itself, +however, the grains of chlorophyll near the cut surfaces had run together, or +become aggregated. Nor were the glands on another leaf, after an immersion for +24 hrs. in an infusion of raw meat, in the least affected; but the protoplasm +lining the cells of the pedicels had shrunk greatly from the walls. This latter +effect may have been due to exosmose, as the infusion was strong. We may, +therefore, conclude that the glands of this plant either have no power of +absorption or that the protoplasm which they contain is not acted on by a +solution of carbonate of ammonia (and this seems scarcely credible) or by an +infusion of meat. +</p> + +<p> +Nicotiana tabacum.—This plant is covered with innumerable hairs of +unequal lengths, which catch many minute insects. The pedicels of the hairs are +divided by transverse partitions, and the secreting glands are formed of many +cells, containing greenish matter with little globules of some substance. +Leaves were left in an infusion of raw meat and in water for 26 hrs., but +presented no difference. Some of these same leaves were then left for above 2 +hrs. in a solution of carbonate of ammonia, but no effect was produced. I +regret that other experiments were not tried with more care, as M. Schloesing +[page 353] has shown* that tobacco plants supplied with the vapour of carbonate +of ammonia yield on analysis a greater amount of nitrogen than other plants not +thus treated; and, from what we have seen, it is probable that some of the +vapour may be absorbed by the glandular hairs.] +</p> + +<p> +A Summary of the Observations on Glandular Hairs.—From the foregoing +observations, few as they are, we see that the glands of two species of +Saxifraga, of a Primula and Pelargonium, have the power of rapid absorption; +whereas the glands of an Erica, Mirabilis, and Nicotiana, either have no such +power, or the contents of the cells are not affected by the fluids employed, +namely a solution of carbonate of ammonia and an infusion of raw meat. As the +glands of the Mirabilis contain protoplasm, which did not become aggregated +from exposure to the fluids just named, though the contents of the cells in the +blade of the leaf were greatly affected by carbonate of ammonia, we may infer +that they cannot absorb. We may further infer that the innumerable insects +caught by this plant are of no more service to it than are those which adhere +to the deciduous and sticky scales of the leaf-buds of the horse-chestnut. +</p> + +<p> +The most interesting case for us is that of the two species of Saxifraga, as +this genus is distantly allied to Drosera. Their glands absorb matter from an +infusion of raw meat, from solutions of the nitrate and carbonate of ammonia, +and apparently from decayed insects. This was shown by the changed dull purple +colour of the protoplasm within the cells of the glands, by its state of +aggregation, and apparently by its more rapid spontaneous movements. +</p> + +<p class="footnote"> +* ‘Comptes rendus,’ June 15, 1874. A good abstract of this paper is +given in the ‘Gardener’s Chronicle,’ July 11, 1874. [page +354] +</p> + +<p> +The aggregating process spreads from the glands down the pedicels of the hairs; +and we may assume that any matter which is absorbed ultimately reaches the +tissues of the plant. On the other hand, the process travels up the hairs +whenever a surface is cut and exposed to a solution of the carbonate of +ammonia. +</p> + +<p> +The glands on the flower-stalks and leaves of Primula sinensis quickly absorb a +solution of the carbonate of ammonia, and the protoplasm which they contain +becomes aggregated. The process was seen in some cases to travel from the +glands into the upper cells of the pedicels. Exposure for 10 m. to the vapour +of this salt likewise induced aggregation. When leaves were left from 6 hrs. to +7 hrs. in a strong solution, or were long exposed to the vapour, the little +masses of protoplasm became disintegrated, brown, and granular, and were +apparently killed. An infusion of raw meat produced no effect on the glands. +</p> + +<p> +The limpid contents of the glands of Pelargonium zonale became cloudy and +granular in from 3 m. to 5 m. when they were immersed in a weak solution of the +carbonate of ammonia; and in the course of 1 hr. granules appeared in the upper +cells of the pedicels. As the aggregated masses slowly changed their forms, and +as they suffered disintegration when left for a considerable time in a strong +solution, there can be little doubt that they consisted of protoplasm. It is +doubtful whether an infusion of raw meat produced any effect. +</p> + +<p> +The glandular hairs of ordinary plants have generally been considered by +physiologists to serve only as secreting or excreting organs, but we now know +that they have the power, at least in some cases, of absorbing both a solution +and the vapour of ammonia. As rain-water contains a small percentage of +ammonia, and the atmosphere a minute quantity of the carbonate, this [page 355] +power can hardly fail to be beneficial. Nor can the benefit be quite so +insignificant as it might at first be thought, for a moderately fine plant of +Primula sinensis bears the astonishing number of above two millions and a half +of glandular hairs,* all of which are able to absorb ammonia brought to them by +the rain. It is moreover probable that the glands of some of the above named +plants obtain animal matter from the insects which are occasionally entangled +by the viscid secretion. +</p> + +<p class="center"> +C<small>ONCLUDING</small> R<small>EMARKS ON THE</small> +D<small>ROSERACEÆ</small>. +</p> + +<p> +The six known genera composing this family have now been described in relation +to our present subject, as far as my means have permitted. They all capture +insects. This is effected by Drosophyllum, Roridula, and Byblis, solely by the +viscid fluid secreted from their glands; by Drosera, through the same means, +together with the movements of the tentacles; by Dionaea and Aldrovanda, +through the closing of the blades of the leaf. In these two last genera rapid +</p> + +<p class="footnote"> +* My son Francis counted the hairs on a space measured by means of a +micrometer, and found that there were 35,336 on a square inch of the upper +surface of a leaf, and 30,035 on the lower surface; that is, in about the +proportion of 100 on the upper to 85 on the lower surface. On a square inch of +both surfaces there were 65,371 hairs. A moderately fine plant bearing twelve +leaves (the larger ones being a little more than 2 inches in diameter) was now +selected, and the area of all the leaves, together with their foot-stalks (the +flower-stems not being included), was found by a planimeter to be 39.285 square +inches; so that the area of both surfaces was 78.57 square inches. Thus the +plant (excluding the flower-stems) must have borne the astonishing number of +2,568,099 glandular hairs. The hairs were counted late in the autumn, and by +the following spring (May) the leaves of some other plants of the same lot were +found to be from one-third to one-fourth broader and longer than they were +before; so that no doubt the glandular hairs had increased in number, and +probably now much exceeded three millions. [page 356] +</p> + +<p> +movement makes up for the loss of viscid secretion. In every case it is some +part of the leaf which moves. In Aldrovanda it appears to be the basal parts +alone which contract and carry with them the broad, thin margins of the lobes. +In Dionaea the whole lobe, with the exception of the marginal prolongations or +spikes, curves inwards, though the chief seat of movement is near the midrib. +In Drosera the chief seat is in the lower part of the tentacles, which, +homologically, may be considered as prolongations of the leaf; but the whole +blade often curls inwards, converting the leaf into a temporary stomach. +</p> + +<p> +There can hardly be a doubt that all the plants belonging to these six genera +have the power of dissolving animal matter by the aid of their secretion, which +contains an acid, together with a ferment almost identical in nature with +pepsin; and that they afterwards absorb the matter thus digested. This is +certainly the case with Drosera, Drosophyllum, and Dionaea; almost certainly +with Aldrovanda; and, from analogy, very probable with Roridula and Byblis. We +can thus understand how it is that the three first-named genera are provided +with such small roots, and that Aldrovanda is quite rootless; about the roots +of the two other genera nothing is known. It is, no doubt, a surprising fact +that a whole group of plants (and, as we shall presently see, some other plants +not allied to the Droseraceae) should subsist partly by digesting animal +matter, and partly by decomposing carbonic acid, instead of exclusively by this +latter means, together with the absorption of matter from the soil by the aid +of roots. We have, however, an equally anomalous case in the animal kingdom; +the rhizocephalous crustaceans do not feed like other animals by their mouths, +for they are destitute of an [page 357] alimentary canal; but they live by +absorbing through root-like processes the juices of the animals on which they +are parasitic.* +</p> + +<p> +Of the six genera, Drosera has been incomparably the most successful in the +battle for life; and a large part of its success may be attributed to its +manner of catching insects. It is a dominant form, for it is believed to +include about 100 species,** which range in the Old World from the Arctic +regions to Southern India, to the Cape of Good Hope, Madagascar, and Australia; +and in the New World from Canada to Tierra del Fuego. In this respect it +presents a marked contrast with the five other genera, which appear to be +failing groups. Dionaea includes only a single species, which is confined to +one district in Carolina. The three varieties or closely allied species of +Aldrovanda, like so many water-plants, have a wide range from Central Europe to +Bengal and Australia. Drosophyllum includes only one species, limited to +Portugal and Morocco. Roridula and Byblis each have (as I +</p> + +<p class="footnote"> +* Fritz Müller, ‘Facts for Darwin,’ Eng. trans. 1869, p. 139. The +rhizocephalous crustaceans are allied to the cirripedes. It is hardly possible +to imagine a greater difference than that between an animal with prehensile +limbs, a well-constructed mouth and alimentary canal, and one destitute of all +these organs and feeding by absorption through branching root-like processes. +If one rare cirripede, the Anelasma squalicola, had become extinct, it would +have been very difficult to conjecture how so enormous a change could have been +gradually effected. But, as Fritz Müller remarks, we have in Anelasma an animal +in an almost exactly intermediate condition, for it has root-like processes +embedded in the skin of the shark on which it is parasitic, and its prehensile +cirri and mouth (as described in my monograph on the Lepadidae, ‘Ray +Soc.’ 1851, p. 169) are in a most feeble and almost rudimentary +condition. Dr. R. Kossmann has given a very interesting discussion on this +subject in his ‘Suctoria and Lepadidae,’ 1873. See also, Dr. Dohrn, +‘Der Ursprung der Wirbelthiere,’ 1875, p. 77. +</p> + +<p class="footnote"> +** Bentham and Hooker, ‘Genera Plantarum.’ Australia is the +metropolis of the genus, forty-one species having been described from this +country, as Prof. Oliver informs me. [page 358] +</p> + +<p> +hear from Prof. Oliver) two species; the former confined to the western parts +of the Cape of Good Hope, and the latter to Australia. It is a strange fact +that Dionaea, which is one of the most beautifully adapted plants in the +vegetable kingdom, should apparently be on the high-road to extinction. This is +all the more strange as the organs of Dionaea are more highly differentiated +than those of Drosera; its filaments serve exclusively as organs of touch, the +lobes for capturing insects, and the glands, when excited, for secretion as +well as for absorption; whereas with Drosera the glands serve all these +purposes, and secrete without being excited. +</p> + +<p> +By comparing the structure of the leaves, their degree of complication, and +their rudimentary parts in the six genera, we are led to infer that their +common parent form partook of the characters of Drosophyllum, Roridula, and +Byblis. The leaves of this ancient form were almost certainly linear, perhaps +divided, and bore on their upper and lower surfaces glands which had the power +of secreting and absorbing. Some of these glands were mounted on pedicels, and +others were almost sessile; the latter secreting only when stimulated by the +absorption of nitrogenous matter. In Byblis the glands consist of a single +layer of cells, supported on a unicellular pedicel; in Roridula they have a +more complex structure, and are supported on pedicels formed of several rows of +cells; in Drosophyllum they further include spiral cells, and the pedicels +include a bundle of spiral vessels. But in these three genera these organs do +not possess any power of movement, and there is no reason to doubt that they +are of the nature of hairs or trichomes. Although in innumerable instances +foliar organs move when excited, no case is known of a trichome having such +[page 359] power.* We are thus led to inquire how the so-called tentacles of +Drosera, which are manifestly of the same general nature as the glandular hairs +of the above three genera, could have acquired the power of moving. Many +botanists maintain that these tentacles consist of prolongations of the leaf, +because they include vascular tissue, but this can no longer be considered as a +trustworthy distinction.** The possession of the power of movement on +excitement would have been safer evidence. But when we consider the vast number +of the tentacles on both surfaces of the leaves of Drosophyllum, and on the +upper surface of the leaves of Drosera, it seems scarcely possible that each +tentacle could have aboriginally existed as a prolongation of the leaf. +Roridula, perhaps, shows us how we may reconcile these difficulties with +respect to the homological nature of the tentacles. The lateral divisions of +the leaves of this plant terminate in long tentacles; and these include spiral +vessels which extend for only a short distance up them, with no line of +demarcation between what is plainly the prolongation of the leaf and the +pedicel of a glandular hair. Therefore there would be nothing anomalous or +unusual in the basal parts of these tentacles, which correspond with the +marginal ones of Drosera, acquiring the power of movement; and we know that in +Drosera it is only the lower part which becomes inflected. But in order to +understand how in this latter genus not only the marginal but all the inner +tentacles have become capable of movement, we must further assume, either that +through the principle of correlated development this +</p> + +<p class="footnote"> +* Sachs, ‘Traité de Botanique’ 3rd edit. 1874, p. 1026. +</p> + +<p class="footnote"> +** Dr. Warming ‘Sur la Diffrence entres les Trichomes,’ Copenhague, +1873, p. 6. ‘Extrait des Videnskabelige Meddelelser de la Soc. +d’Hist. nat. de Copenhague,’ Nos. 10-12, 1872. [page 360] +</p> + +<p> +power was transferred to the basal parts of the hairs, or that the surface of +the leaf has been prolonged upwards at numerous points, so as to unite with the +hairs, thus forming the bases of the inner tentacles. +</p> + +<p> +The above named three genera, namely Drosophyllum, Roridula, and Byblis, which +appear to have retained a primordial condition, still bear glandular hairs on +both surfaces of their leaves; but those on the lower surface have since +disappeared in the more highly developed genera, with the partial exception of +one species, Drosera binata. The small sessile glands have also disappeared in +some of the genera, being replaced in Roridula by hairs, and in most species of +Drosera by absorbent papillae. Drosera binata, with its linear and bifurcating +leaves, is in an intermediate condition. It still bears some sessile glands on +both surfaces of the leaves, and on the lower surface a few irregularly placed +tentacles, which are incapable of movement. A further slight change would +convert the linear leaves of this latter species into the oblong leaves of +Drosera anglica, and these might easily pass into orbicular ones with +footstalks, like those of Drosera rotundifolia. The footstalks of this latter +species bear multicellular hairs, which we have good reason to believe +represent aborted tentacles. +</p> + +<p> +The parent form of Dionaea and Aldrovanda seems to have been closely allied to +Drosera, and to have had rounded leaves, supported on distinct footstalks, and +furnished with tentacles all round the circumference, with other tentacles and +sessile glands on the upper surface. I think so because the marginal spikes of +Dionaea apparently represent the extreme marginal tentacles of Drosera, the six +(sometimes eight) sensitive filaments on the upper surface, as well as the more +numerous ones in Aldrovanda, representing the central [page 361] tentacles of +Drosera, with their glands aborted, but their sensitiveness retained. Under +this point of view we should bear in mind that the summits of the tentacles of +Drosera, close beneath the glands, are sensitive. +</p> + +<p> +The three most remarkable characters possessed by the several members of the +Droseraceae consist in the leaves of some having the power of movement when +excited, in their glands secreting a fluid which digests animal matter, and in +their absorption of the digested matter. Can any light be thrown on the steps +by which these remarkable powers were gradually acquired? +</p> + +<p> +As the walls of the cells are necessarily permeable to fluids, in order to +allow the glands to secrete, it is not surprising that they should readily +allow fluids to pass inwards; and this inward passage would deserve to be +called an act of absorption, if the fluids combined with the contents of the +glands. Judging from the evidence above given, the secreting glands of many +other plants can absorb salts of ammonia, of which they must receive small +quantities from the rain. This is the case with two species of Saxifraga, and +the glands of one of them apparently absorb matter from captured insects, and +certainly from an infusion of raw meat. There is, therefore, nothing anomalous +in the Droseraceae having acquired the power of absorption in a much more +highly developed degree. +</p> + +<p> +It is a far more remarkable problem how the members of this family, and +Pinguicula, and, as Dr. Hooker has recently shown, Nepenthes, could all have +acquired the power of secreting a fluid which dissolves or digests animal +matter. The six genera of the Droseraceae very probably inherited this power +from a common progenitor, but this cannot apply to [page 362] Pinguicula or +Nepenthes, for these plants are not at all closely related to the Droceraceae. +But the difficulty is not nearly so great as it at first appears. Firstly, the +juices of many plants contain an acid, and, apparently, any acid serves for +digestion. Secondly, as Dr. Hooker has remarked in relation to the present +subject in his address at Belfast (1874), and as Sachs repeatedly insists,* the +embryos of some plants secrete a fluid which dissolves albuminous substances +out of the endosperm; although the endosperm is not actually united with, only +in contact with, the embryo. All plants, moreover, have the power of dissolving +albuminous or proteid substances, such as protoplasm, chlorophyll, gluten, +aleurone, and of carrying them from one part to other parts of their tissues. +This must be effected by a solvent, probably consisting of a ferment together +with an acid.** Now, in the case of plants which are able to absorb already +soluble matter from captured insects, though not capable of true digestion, the +solvent just referred to, which must be occasionally present in the glands, +would be apt to exude from the glands together with the viscid secretion, +inasmuch as endosmose is accompanied by exosmose. If such exudation did ever +occur, the solvent would act on the animal matter contained within the captured +insects, and this would be an act of true digestion. As it cannot be doubted +that this process would be of high service to plants +</p> + +<p class="footnote"> +* ‘Traité de Botanique’ 3rd edit. 1874, p. 844. See also for +following facts pp. 64, 76, 828, 831. +</p> + +<p class="footnote"> +** Since this sentence was written, I have received a paper by Gorup-Besanez +(‘Berichte der Deutschen Chem. Gesellschaft,’ Berlin, 1874, p. +1478), who, with the aid of Dr. H. Will, has actually made the discovery that +the seeds of the vetch contain a ferment, which, when extracted by glycerine, +dissolves albuminous substances, such as fibrin, and converts them into true +peptones. [page 363] +</p> + +<p> +growing in very poor soil, it would tend to be perfected through natural +selection. Therefore, any ordinary plant having viscid glands, which +occasionally caught insects, might thus be converted under favourable +circumstances into a species capable of true digestion. It ceases, therefore, +to be any great mystery how several genera of plants, in no way closely related +together, have independently acquired this same power. +</p> + +<p> +As there exist several plants the glands of which cannot, as far as is known, +digest animal matter, yet can absorb salts of ammonia and animal fluids, it is +probable that this latter power forms the first stage towards that of +digestion. It might, however, happen, under certain conditions, that a plant, +after having acquired the power of digestion, should degenerate into one +capable only of absorbing animal matter in solution, or in a state of decay, or +the final products of decay, namely the salts of ammonia. It would appear that +this has actually occurred to a partial extent with the leaves of Aldrovanda; +the outer parts of which possess absorbent organs, but no glands fitted for the +secretion of any digestive fluid, these being confined to the inner parts. +</p> + +<p> +Little light can be thrown on the gradual acquirement of the third remarkable +character possessed by the more highly developed genera of the Droseraceae, +namely the power of movement when excited. It should, however, be borne in mind +that leaves and their homologues, as well as flower-peduncles, have gained this +power, in innumerable instances, independently of inheritance from any common +parent form; for instance, in tendril-bearers and leaf-climbers (i.e. plants +with their leaves, petioles and flower-peduncles, &c., modified for +prehension) belonging to a large [page 364] number of the most widely distinct +orders,—in the leaves of the many plants which go to sleep at night, or +move when shaken,—and in the irritable stamens and pistils of not a few +species. We may therefore infer that the power of movement can be by some means +readily acquired. Such movements imply irritability or sensitiveness, but, as +Cohn has remarked,* the tissues of the plants thus endowed do not differ in any +uniform manner from those of ordinary plants; it is therefore probable that all +leaves are to a slight degree irritable. Even if an insect alights on a leaf, a +slight molecular change is probably transmitted to some distance across its +tissue, with the sole difference that no perceptible effect is produced. We +have some evidence in favour of this belief, for we know that a single touch on +the glands of Drosera does not excite inflection; yet it must produce some +effect, for if the glands have been immersed in a solution of camphor, +inflection follows within a shorter time than would have followed from the +effects of camphor alone. So again with Dionaea, the blades in their ordinary +state may be roughly touched without their closing; yet some effect must be +thus caused and transmitted across the whole leaf, for if the glands have +recently absorbed animal matter, even a delicate touch causes them to close +instantly. On the whole we may conclude that the acquirement of a high degree +of sensitiveness and of the power of movement by certain genera of the +Droseraceae presents no greater difficulty than that presented by the similar +but feebler powers of a multitude of other plants. +</p> + +<p class="footnote"> +* See the abstract of his memoir on the contractile tissues of plants, in the +‘Annals and Mag. of Nat. Hist.’ 3rd series, vol. xi. p. 188.) [page +365] +</p> + +<p> +The specialised nature of the sensitiveness possessed by Drosera and Dionaea, +and by certain other plants, well deserves attention. A gland of Drosera may be +forcibly hit once, twice, or even thrice, without any effect being produced, +whilst the continued pressure of an extremely minute particle excites movement. +On the other hand, a particle many times heavier may be gently laid on one of +the filaments of Dionaea with no effect; but if touched only once by the slow +movement of a delicate hair, the lobes close; and this difference in the nature +of the sensitiveness of these two plants stands in manifest adaptation to their +manner of capturing insects. So does the fact, that when the central glands of +Drosera absorb nitrogenous matter, they transmit a motor impulse to the +exterior tentacles much more quickly than when they are mechanically irritated; +whilst with Dionaea the absorption of nitrogenous matter causes the lobes to +press together with extreme slowness, whilst a touch excites rapid movement. +Somewhat analogous cases may be observed, as I have shown in another work, with +the tendrils of various plants; some being most excited by contact with fine +fibres, others by contact with bristles, others with a flat or a creviced +surface. The sensitive organs of Drosera and Dionaea are also specialised, so +as not to be uselessly affected by the weight or impact of drops of rain, or by +blasts of air. This may be accounted for by supposing that these plants and +their progenitors have grown accustomed to the repeated action of rain and +wind, so that no molecular change is thus induced; whilst they have been +rendered more sensitive by means of natural selection to the rarer impact or +pressure of solid bodies. Although the absorption by the glands of Drosera of +various fluids excites move- [page 366] ment, there is a great difference in +the action of allied fluids; for instance, between certain vegetable acids, and +between citrate and phosphate of ammonia. The specialised nature and perfection +of the sensitiveness in these two plants is all the more astonishing as no one +supposes that they possess nerves; and by testing Drosera with several +substances which act powerfully on the nervous system of animals, it does not +appear that they include any diffused matter analogous to nerve-tissue. +</p> + +<p> +Although the cells of Drosera and Dionaea are quite as sensitive to certain +stimulants as are the tissues which surround the terminations of the nerves in +the higher animals, yet these plants are inferior even to animals low down in +the scale, in not being affected except by stimulants in contact with their +sensitive parts. They would, however, probably be affected by radiant heat; for +warm water excites energetic movement. When a gland of Drosera, or one of the +filaments of Dionaea, is excited, the motor impulse radiates in all directions, +and is not, as in the case of animals, directed towards special points or +organs. This holds good even in the case of Drosera when some exciting +substance has been placed at two points on the disc, and when the tentacles all +round are inflected with marvellous precision towards the two points. The rate +at which the motor impulse is transmitted, though rapid in Dionaea, is much +slower than in most or all animals. This fact, as well as that of the motor +impulse not being specially directed to certain points, are both no doubt due +to the absence of nerves. Nevertheless we perhaps see the prefigurement of the +formation of nerves in animals in the transmission of the motor impulse being +so much more rapid down the confined space within the tentacles of Drosera than +[page 367] elsewhere, and somewhat more rapid in a longitudinal than in a +transverse direction across the disc. These plants exhibit still more plainly +their inferiority to animals in the absence of any reflex action, except in so +far as the glands of Drosera, when excited from a distance, send back some +influence which causes the contents of the cells to become aggregated down to +the bases of the tentacles. But the greatest inferiority of all is the absence +of a central organ, able to receive impressions from all points, to transmit +their effects in any definite direction, to store them up and reproduce them. +[page 368] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0016" id="link2HCH0016"></a> +CHAPTER XVI.<br/> +PINGUICULA.</h2> + +<p class="letter"> +Pinguicula vulgaris—Structure of leaves—Number of insects and other +objects caught— Movement of the margins of the leaves—Uses of this +movement—Secretion, digestion, and absorption—Action of the +secretion on various animal and vegetable substances—The effects of +substances not containing soluble nitrogenous matter on the +glands—Pinguicula grandiflora—Pinguicula lusitanica, catches +insects—Movement of the leaves, secretion and digestion. +</p> + +<p> +Pinguicula vulgaris.—This plant grows in moist places, generally on +mountains. It bears on an average eight, rather thick, oblong, light green +leaves, having scarcely any footstalk. A full-sized leaf is about 1 1/2 inch in +length and 3/4 inch in breadth. The young central leaves are deeply concave, +and project upwards; the older ones towards the outside are flat or convex, and +lie close to the ground, forming a rosette from 3 to 4 inches in diameter. The +margins of the leaves are incurved. Their upper surfaces are thickly covered +with two sets of glandular hairs, differing in the size of the glands and in +the length of their pedicels. The larger glands have a circular outline as seen +from above, and are of moderate thickness; they are divided by radiating +partitions into sixteen cells, containing light-green, homogeneous fluid. They +are supported on elongated, unicellular pedicels (containing a nucleus with a +nucleolus) which rest on slight prominences. The small glands differ only in +being formed of about half the number of cells, containing much paler fluid, +and supported on much shorter pedicels. Near the midrib, towards the base of +the leaf, the [page 369] pedicels are multicellular, are longer than elsewhere, +and bear smaller glands. All the glands secrete a colourless fluid, which is so +viscid that I have seen a fine thread drawn out to a length of 18 inches; but +the fluid in this case was secreted by a gland which had been excited. The edge +of the leaf is translucent, and does not bear any glands; and here the spiral +vessels, proceeding from the midrib, terminate in cells marked by a spiral +line, somewhat like those within the glands of Drosera. +</p> + +<p> +The roots are short. Three plants were dug up in North Wales on June 20, and +carefully washed; each bore five or six unbranched roots, the longest of which +was only 1.2 of an inch. Two rather young plants were examined on September 28; +these had a greater number of roots, namely eight and eighteen, all under 1 +inch in length, and very little branched. +</p> + +<p> +I was led to investigate the habits of this plant by being told by Mr. W. +Marshall that on the mountains of Cumberland many insects adhere to the leaves. +</p> + +<p> +[A friend sent me on June 23 thirty-nine leaves from North Wales, which were +selected owing to objects of some kind adhering to them. Of these leaves, +thirty-two had caught 142 insects, or on an average 4.4 per leaf, minute +fragments of insects not being included. Besides the insects, small leaves +belonging to four different kinds of plants, those of Erica tetralix being much +the commonest, and three minute seedling plants, blown by the wind, adhered to +nineteen of the leaves. One had caught as many as ten leaves of the Erica. +Seeds or fruits, commonly of Carex and one of Juncus, besides bits of moss and +other rubbish, likewise adhered to six of the thirty-nine leaves. The same +friend, on June 27, collected nine plants bearing seventy-four leaves, and all +of these, with the exception of three young leaves, had caught insects; thirty +insects were counted on one leaf, eighteen on a second, and sixteen on a third. +Another friend examined on August 22 some plants in Donegal, Ireland, and found +insects on 70 out of 157 leaves; fifteen of [page 370] these leaves were sent +me, each having caught on an average 2.4 insects. To nine of them, leaves +(mostly of Erica tetralix) adhered; but they had been specially selected on +this latter account. I may add that early in August my son found leaves of this +same Erica and the fruits of a Carex on the leaves of a Pinguicula in +Switzerland, probably Pinguicula alpina; some insects, but no great number, +also adhered to the leaves of this plant, which had much better developed roots +than those of Pinguicula vulgaris. In Cumberland, Mr. Marshall, on September 3, +carefully examined for me ten plants bearing eighty leaves; and on sixty-three +of these (i.e. on 79 per cent.) he found insects, 143 in number; so that each +leaf had on an average 2.27 insects. A few days later he sent me some plants +with sixteen seeds or fruits adhering to fourteen leaves. There was a seed on +three leaves on the same plant. The sixteen seeds belonged to nine different +kinds, which could not be recognised, excepting one of Ranunculus, and several +belonging to three or four distinct species of Carex. It appears that fewer +insects are caught late in the year than earlier; thus in Cumberland from +twenty to twenty-four insects were observed in the middle of July on several +leaves, whereas in the beginning of September the average number was only 2.27. +Most of the insects, in all the foregoing cases, were Diptera, but with many +minute Hymenoptera, including some ants, a few small Coleoptera, larvæ, +spiders, and even small moths.] +</p> + +<p> +We thus see that numerous insects and other objects are caught by the viscid +leaves; but we have no right to infer from this fact that the habit is +beneficial to the plant, any more than in the before given case of the +Mirabilis, or of the horse-chestnut. But it will presently be seen that dead +insects and other nitrogenous bodies excite the glands to increased secretion; +and that the secretion then becomes acid and has the power of digesting animal +substances, such as albumen, fibrin, &c. Moreover, the dissolved +nitrogenous matter is absorbed by the glands, as shown by their limpid contents +being aggregated into slowly moving granular masses of protoplasm. The same +results follow when insects are naturally captured, and as the plant lives in +poor soil and has small roots, there can be no [page 371] doubt that it profits +by its power of digesting and absorbing matter from the prey which it +habitually captures in such large numbers. It will, however, be convenient +first to describe the movements of the leaves. +</p> + +<p> +Movements of the Leaves.—That such thick, large leaves as those of +Pinguicula vulgarisshould have the power of curving inwards when excited has +never even been suspected. It is necessary to select for experiment leaves with +their glands secreting freely, and which have been prevented from capturing +many insects; as old leaves, at least those growing in a state of nature, have +their margins already curled so much inwards that they exhibit little power of +movement, or move very slowly. I will first give in detail the more important +experiments which were tried, and then make some concluding remarks. +</p> + +<p> +[Experiment 1.—A young and almost upright leaf was selected, with its two +lateral edges equally and very slightly incurved. A row of small flies was +placed along one margin. When looked at next day, after 15 hrs., this margin, +but not the other, was found folded inwards, like the helix of the human ear, +to the breadth of 1/10 of an inch, so as to lie partly over the row of flies +(fig. 15). The glands on which the flies rested, as well as those on the +over-lapping margin which had been brought into contact with the flies, were +all secreting copiously. +</p> + +<p> +FIG. 15. (Pinguicula vulgaris.) Outline of leaf with left margin inflected over +a row of small flies. +</p> + +<p> +Experiment 2.—A row of flies was placed on one margin of a rather old +leaf, which lay flat on the ground; and in this case the margin, after the same +interval as before, namely 15 hrs., had only just begun to curl inwards; but so +much secretion had been poured forth that the spoon-shaped tip of the leaf was +filled with it. +</p> + +<p> +Experiment 3.—Fragments of a large fly were placed close to the apex of a +vigorous leaf, as well as along half one margin. [page 372] After 4 hrs. 20 m. +there was decided incurvation, which increased a little during the afternoon, +but was in the same state on the following morning. Near the apex both margins +were inwardly curved. I have never seen a case of the apex itself being in the +least curved towards the base of the leaf. After 48 hrs. (always reckoning from +the time when the flies were placed on the leaf) the margin had everywhere +begun to unfold. +</p> + +<p> +Experiment 4.—A large fragment of a fly was placed on a leaf, in a medial +line, a little beneath the apex. Both lateral margins were perceptibly incurved +in 3 hrs., and after 4 hrs. 20 m. to such a degree that the fragment was +clasped by both margins. After 24 hrs. the two infolded edges near the apex +(for the lower part of the leaf was not at all affected) were measured and +found to be .11 of an inch (2.795 mm.) apart. The fly was now removed, and a +stream of water poured over the leaf so as to wash the surface; and after 24 +hrs. the margins were .25 of an inch (6.349 mm.) apart, so that they were +largely unfolded. After an additional 24 hrs. they were completely unfolded. +Another fly was now put on the same spot to see whether this leaf, on which the +first fly had been left 24 hrs., would move again; after 10 hrs. there was a +trace of incurvation, but this did not increase during the next 24 hrs. A bit +of meat was also placed on the margin of a leaf, which four days previously had +become strongly incurved over a fragment of a fly and had afterwards +re-expanded; but the meat did not cause even a trace of incurvation. On the +contrary, the margin became somewhat reflexed, as if injured, and so remained +for the three following days, as long as it was observed. +</p> + +<p> +Experiment 5.—A large fragment of a fly was placed halfway between the +apex and base of a leaf and halfway between the midrib and one margin. A short +space of this margin, opposite the fly, showed a trace of incurvation after 3 +hrs., and this became strongly pronounced in 7 hrs. After 24 hrs. the infolded +edge was only .16 of an inch (4.064 mm.) from the midrib. The margin now began +to unfold, though the fly was left on the leaf; so that by the next morning +(i.e. 48 hrs. from the time when the fly was first put on) the infolded edge +had almost completely recovered its original position, being now .3 of an inch +(7.62 mm.), instead of .16 of an inch, from the midrib. A trace of flexure was, +however, still visible. +</p> + +<p> +Experiment 6.—A young and concave leaf was selected with its margins +slightly and naturally incurved. Two rather large, oblong, rectangular pieces +of roast meat were placed with their ends touching the infolded edge, and .46 +of an inch (11.68 mm.) [page 373] apart from one another. After 24 hrs. the +margin was greatly and equally incurved (see fig. 16) throughout this space, +and for a length of .12 or .13 of an inch (3.048 or 3.302 mm.) above and below +each bit; so that the margin had been affected over a greater length between +the two bits, owing to their conjoint action, than beyond them. The bits of +meat were too large to be clasped by the margin, but they were tilted up, one +of them so as to stand almost vertically. After 48 hrs. the margin was almost +unfolded, and the bits had sunk down. When again examined after two days, the +margin was quite unfolded, with the exception of the naturally inflected edge; +and one of the bits of meat, the end of which had at first touched the edge, +was now .067 of an inch (1.70 mm.) distant from it; so that this bit had been +pushed thus far across the blade of the leaf. +</p> + +<p> +FIG. 16. (Pinguicula vulgaris.) Outline of leaf, with right margin inflected +against two square bits of meat. +</p> + +<p> +Experiment 7.—A bit of meat was placed close to the incurved edge of a +rather young leaf, and after it had re-expanded, the bit was left lying .11 of +an inch (2.795 mm.) from the edge. The distance from the edge to the midrib of +the fully expanded leaf was .35 of an inch (8.89 mm.); so that the bit had been +pushed inwards and across nearly one-third of its semi-diameter. +</p> + +<p> +Experiment 8.—Cubes of sponge, soaked in a strong infusion of raw meat, +were placed in close contact with the incurved edges of two leaves,—an +older and younger one. The distance from the edges to the midribs was carefully +measured. After 1 hr. 17 m. there appeared to be a trace of incurvation. After +2 hrs. 17 m. both leaves were plainly inflected; the distance between the edges +and midribs being now only half what it was at first. The incurvation increased +slightly during the next 4 1/2 hrs., but remained nearly the same for the next +17 hrs. 30 m. In 35 hrs. from the time when the sponges were placed on the +leaves, the margins were a little unfolded—to a greater degree in the +younger than in the older leaf. The latter was not quite unfolded until the +third day, and now both bits of sponge were left at the distance of .1 of an +inch (2.54 mm.) from the edges; or about a quarter of the distance between the +edge and midrib. A third bit of sponge adhered to the edge, and, as the margin +unfolded, was dragged backwards, into its original position. [page 374] +</p> + +<p> +Experiment 9.—A chain of fibres of roast meat, as thin as bristles and +moistened with saliva, were placed down one whole side, close to the narrow, +naturally incurved edge of a leaf. In 3 hrs. this side was greatly incurved +along its whole length, and after 8 hrs. formed a cylinder, about 1/20 of an +inch (1.27 mm) in diameter, quite concealing the meat. This cylinder remained +closed for 32 hrs., but after 48 hrs. was half unfolded, and in 72 hrs. was as +open as the opposite margin where no meat had been placed. As the thin fibres +of meat were completely overlapped by the margin, they were not pushed at all +inwards, across the blade. +</p> + +<p> +Experiment 10.—Six cabbage seeds, soaked for a night in water, were +placed in a row close to the narrow incurved edge of a leaf. We shall hereafter +see that these seeds yield soluble matter to the glands. In 2 hrs. 25 m. the +margin was decidedly inflected; in 4 hrs. it extended over the seeds for about +half their breadth, and in 7 hrs. over three-fourths of their breadth, forming +a cylinder not quite closed along the inner side, and about .7 of an inch +(1.778 mm.) in diameter. After 24 hrs. the inflection had not increased, +perhaps had decreased. The glands which had been brought into contact with the +upper surfaces of the seeds were now secreting freely. In 36 hrs. from the time +when the seeds were put on the leaf the margin had greatly, and after 48 hrs. +had completely, re-expanded. As the seeds were no longer held by the inflected +margin, and as the secretion was beginning to fail, they rolled some way down +the marginal channel. +</p> + +<p> +Experiment 11.—Fragments of glass were placed on the margins of two fine +young leaves. After 2 hrs. 30 m. the margin of one certainly became slightly +incurved; but the inflection never increased, and disappeared in 16 hrs. 30 m. +from the time when the fragments were first applied. With the second leaf there +was a trace of incurvation in 2 hrs. 15 m., which became decided in 4 hrs. 30 +m., and still more strongly pronounced in 7 hrs., but after 19 hrs. 30 m. had +plainly decreased. The fragments excited at most a slight and doubtful increase +of the secretion; and in two other trials, no increase could be perceived. Bits +of coal-cinders, placed on a leaf, produced no effect, either owing to their +lightness or to the leaf being torpid. +</p> + +<p> +Experiment 12.—We now turn to fluids. A row of drops of a strong infusion +of raw meat were placed along the margins of two leaves; squares of sponge +soaked in the same infusion being placed on the opposite margins. My object was +to ascer- [page 375] tain whether a fluid would act as energetically as a +substance yielding the same soluble matter to the glands. No distinct +difference was perceptible; certainly none in the degree of incurvation; but +the incurvation round the bits of sponge lasted rather longer, as might perhaps +have been expected from the sponge remaining damp and supplying nitrogenous +matter for a longer time. The margins, with the drops, became plainly incurved +in 2 hrs. 17 m. The incurvation subsequently increased somewhat, but after 24 +hrs. had greatly decreased. +</p> + +<p> +Experiment 13.—Drops of the same strong infusion of raw meat were placed +along the midrib of a young and rather deeply concave leaf. The distance across +the broadest part of the leaf, between the naturally incurved edges, was .55 of +an inch (13.97 mm.). In 3 hrs. 27 m. this distance was a trace less; in 6 hrs. +27 m. it was exactly .45 of an inch (11.43 mm.), and had therefore decreased by +.1 of an inch (2.54 mm.). After only 10 hrs. 37 m. the margin began to +re-expand, for the distance from edge to edge was now a trace wider, and after +24 hrs. 20 m. was as great, within a hair’s breadth, as when the drops +were first placed on the leaf. From this experiment we learn that the motor +impulse can be transmitted to a distance of .22 of an inch (5.590 mm.) in a +transverse direction from the midrib to both margins; but it would be safer to +say .2 of an inch (5.08 mm.) as the drops spread a little beyond the midrib. +The incurvation thus caused lasted for an unusually short time. +</p> + +<p> +Experiment 14.—Three drops of a solution of one part of carbonate of +ammonia to 218 of water (2 grs. to 1 oz.) were placed on the margin of a leaf. +These excited so much secretion that in 1 h. 22 m. all three drops ran +together; but although the leaf was observed for 24 hrs., there was no trace of +inflection. We know that a rather strong solution of this salt, though it does +not injure the leaves of Drosera, paralyses their power of movement, and I have +no doubt, from the following case, that this holds good with Pinguicula. +</p> + +<p> +Experiment 15.—A row of drops of a solution of one part of carbonate of +ammonia to 875 of water (1 gr. to 2 oz.) was placed on the margin of a leaf. In +1 hr. there was apparently some slight incurvation, and this was well-marked in +3 hrs. 30 m. After 24 hrs. the margin was almost completely re-expanded. +</p> + +<p> +Experiment 16.—A row of large drops of a solution of one part of +phosphate of ammonia to 4375 of water (1 gr. to 10 oz.) was placed along the +margin of a leaf. No effect was produced, and after 8 hrs. fresh drops were +added along the same margin without the least effect. We know that a solution +of this [page 376] strength acts powerfully on Drosera, and it is just possible +that the solution was too strong. I regret that I did not try a weaker +solution. +</p> + +<p> +Experiment 17.—As the pressure from bits of glass causes incurvation, I +scratched the margins of two leaves for some minutes with a blunt needle, but +no effect was produced. The surface of a leaf beneath a drop of a strong +infusion of raw meat was also rubbed for 10. m. with the end of a bristle, so +as to imitate the struggles of a captured insect; but this part of the margin +did not bend sooner than the other parts with undisturbed drops of the +infusion.] +</p> + +<p> +We learn from the foregoing experiments that the margins of the leaves curl +inwards when excited by the mere pressure of objects not yielding any soluble +matter, by objects yielding such matter, and by some fluids—namely an +infusion of raw meat and a week solution of carbonate of ammonia. A stronger +solution of two grains of this salt to an ounce of water, though exciting +copious secretion, paralyses the leaf. Drops of water and of a solution of +sugar or gum did not cause any movement. Scratching the surface of the leaf for +some minutes produced no effect. Therefore, as far as we at present know, only +two causes—namely slight continued pressure and the absorption of +nitrogenous matter—excite movement. It is only the margins of the leaf +which bend, for the apex never curves towards the base. The pedicels of the +glandular hairs have no power of movement. I observed on several occasions that +the surface of the leaf became slightly concave where bits of meat or large +flies had long lain, but this may have been due to injury from +over-stimulation. +</p> + +<p> +The shortest time in which plainly marked movement was observed was 2 hrs. 17 +m., and this occurred when either nitrogenous substances or fluids were placed +on the leaves; but I believe that in some cases [page 377] there was a trace of +movement in 1 hr. or 1 hr. 30 m. The pressure from fragments of glass excites +movement almost as quickly as the absorption of nitrogenous matter, but the +degree of incurvation thus caused is much less. After a leaf has become well +incurved and has again expanded, it will not soon answer to a fresh stimulus. +The margin was affected longitudinally, upwards or downwards, for a distance of +.13 of an inch (3.302 mm.) from an excited point, but for a distance of .46 of +an inch between two excited points, and transversely for a distance of .2 of an +inch (5.08 mm.). The motor impulse is not accompanied, as in the case of +Drosera, by any influence causing increased secretion; for when a single gland +was strongly stimulated and secreted copiously, the surrounding glands were not +in the least affected. The incurvation of the margin is independent of +increased secretion, for fragments of glass cause little or no secretion, and +yet excite movement; whereas a strong solution of carbonate of ammonia quickly +excites copious secretion, but no movement. +</p> + +<p> +One of the most curious facts with respect to the movement of the leaves is the +short time during which they remain incurved, although the exciting object is +left on them. In the majority of cases there was well-marked re-expansion +within 24 hrs. from the time when even large pieces of meat, &c., were +placed on the leaves, and in all cases within 48 hrs. In one instance the +margin of a leaf remained for 32 hrs. closely inflected round thin fibres of +meat; in another instance, when a bit of sponge, soaked in a strong infusion of +raw meat, had been applied to a leaf, the margin began to unfold in 35 hrs. +Fragments of glass keep the margin incurved for a shorter time than do +nitrogenous bodies; for in the former case there was [page 378] complete +re-expansion in 16 hrs. 30 m. Nitrogenous fluids act for a shorter time than +nitrogenous substances; thus, when drops of an infusion of raw meat were placed +on the midrib of a leaf, the incurved margins began to unfold in only 10 hrs. +37 m., and this was the quickest act of re-expansion observed by me; but it may +have been partly due to the distance of the margins from the midrib where the +drops lay. +</p> + +<p> +We are naturally led to inquire what is the use of this movement which lasts +for so short a time? If very small objects, such as fibres of meat, or +moderately small objects, such as little flies or cabbage-seeds, are placed +close to the margin, they are either completely or partially embraced by it. +The glands of the overlapping margin are thus brought into contact with such +objects and pour forth their secretion, afterwards absorbing the digested +matter. But as the incurvation lasts for so short a time, any such benefit can +be of only slight importance, yet perhaps greater than at first appears. The +plant lives in humid districts, and the insects which adhere to all parts of +the leaf are washed by every heavy shower of rain into the narrow channel +formed by the naturally incurved edges. For instance, my friend in North Wales +placed several insects on some leaves, and two days afterwards (there having +been heavy rain in the interval) found some of them quite washed away, and many +others safely tucked under the now closely inflected margins, the glands of +which all round the insects were no doubt secreting. We can thus, also, +understand how it is that so many insects, and fragments of insects, are +generally found lying within the incurved margins of the leaves. +</p> + +<p> +The incurvation of the margin, due to the presence of an exciting object, must +be serviceable in another [page 379] and probably more important way. We have +seen that when large bits of meat, or of sponge soaked in the juice of meat, +were placed on a leaf, the margin was not able to embrace them, but, as it +became incurved, pushed them very slowly towards the middle of the leaf, to a +distance from the outside of fully .1 of an inch (2.54 mm.), that is, across +between one-third and one-fourth of the space between the edge and midrib. Any +object, such as a moderately sized insect, would thus be brought slowly into +contact with a far larger number of glands, inducing much more secretion and +absorption, than would otherwise have been the case. That this would be highly +serviceable to the plant, we may infer from the fact that Drosera has acquired +highly developed powers of movement, merely for the sake of bringing all its +glands into contact with captured insects. So again, after a leaf of Dionaea +has caught an insect, the slow pressing together of the two lobes serves merely +to bring the glands on both sides into contact with it, causing also the +secretion charged with animal matter to spread by capillary attraction over the +whole surface. In the case of Pinguicula, as soon as an insect has been pushed +for some little distance towards the midrib, immediate re-expansion would be +beneficial, as the margins could not capture fresh prey until they were +unfolded. The service rendered by this pushing action, as well as that from the +marginal glands being brought into contact for a short time with the upper +surfaces of minute captured insects, may perhaps account for the peculiar +movements of the leaves; otherwise, we must look at these movements as a +remnant of a more highly developed power formerly possessed by the progenitors +of the genus. +</p> + +<p> +In the four British species, and, as I hear from [page 380] Prof. Dyer, in most +or all the species of the genus, the edges of the leaves are in some degree +naturally and permanently incurved. This incurvation serves, as already shown, +to prevent insects from being washed away by the rain; but it likewise serves +for another end. When a number of glands have been powerfully excited by bits +of meat, insects, or any other stimulus, the secretion often trickles down the +leaf, and is caught by the incurved edges, instead of rolling off and being +lost. As it runs down the channel, fresh glands are able to absorb the animal +matter held in solution. Moreover, the secretion often collects in little pools +within the channel, or in the spoon-like tips of the leaves; and I ascertained +that bits of albumen, fibrin, and gluten, are here dissolved more quickly and +completely than on the surface of the leaf, where the secretion cannot +accumulate; and so it would be with naturally caught insects. The secretion was +repeatedly seen thus to collect on the leaves of plants protected from the +rain; and with exposed plants there would be still greater need of some +provision to prevent, as far as possible, the secretion, with its dissolved +animal matter, being wholly lost. +</p> + +<p> +It has already been remarked that plants growing in a state of nature have the +margins of their leaves much more strongly incurved than those grown in pots +and prevented from catching many insects. We have seen that insects washed down +by the rain from all parts of the leaf often lodge within the margins, which +are thus excited to curl farther inwards; and we may suspect that this action, +many times repeated during the life of the plant, leads to their permanent and +well-marked incurvation. I regret that this view did not occur to me in time to +test its truth. +</p> + +<p> +It may here be added, though not immediately [page 381] bearing on our subject, +that when a plant is pulled up, the leaves immediately curl downwards so as +almost to conceal the roots,—a fact which has been noticed by many +persons. I suppose that this is due to the same tendency which causes the outer +and older leaves to lie flat on the ground. It further appears that the +flower-stalks are to a certain extent irritable, for Dr. Johnson states that +they “bend backwards if rudely handled.”* +</p> + +<p> +Secretion, Absorption, and Digestion.—I will first give my observations +and experiments, and then a summary of the results. +</p> + +<p> +[The Effects of Objects containing Soluble Nitrogenous Matter. +</p> + +<p> +(1) Flies were placed on many leaves, and excited the glands to secrete +copiously; the secretion always becoming acid, though not so before. After a +time these insects were rendered so tender that their limbs and bodies could be +separated by a mere touch, owing no doubt to the digestion and disintegration +of their muscles. The glands in contact with a small fly continued to secrete +for four days, and then became almost dry. A narrow strip of this leaf was cut +off, and the glands of the longer and shorter hairs, which had lain in contact +for the four days with the fly, and those which had not touched it, were +compared under the microscope and presented a wonderful contrast. Those which +had been in contact were filled with brownish granular matter, the others with +homogeneous fluid. There could therefore be no doubt that the former had +absorbed matter from the fly. +</p> + +<p> +(2) Small bits of roast meat, placed on a leaf, always caused much acid +secretion in the course of a few hours—in one case within 40 m. When thin +fibres of meat were laid along the margin of a leaf which stood almost upright, +the secretion ran down to the ground. Angular bits of meat, placed in little +pools of the secretion near the margin, were in the course of +</p> + +<p class="footnote"> +* ‘English Botany,’ by Sir J.E. Smith; with coloured figures by J. +Sowerby; edit. of 1832, tab. 24, 25, 26. [page 382] +</p> + +<p> +two or three days much reduced in size, rounded, rendered more or less +colourless and transparent, and so much softened that they fell to pieces on +the slightest touch. In only one instance was a very minute particle completely +dissolved, and this occurred within 48 hrs. When only a small amount of +secretion was excited, this was generally absorbed in from 24 hrs. to 48 hrs.; +the glands being left dry. But when the supply of secretion was copious, round +either a single rather large bit of meat, or round several small bits, the +glands did not become dry until six or seven days had elapsed. The most rapid +case of absorption observed by me was when a small drop of an infusion of raw +meat was placed on a leaf, for the glands here became almost dry in 3 hrs. 20 +m. Glands excited by small particles of meat, and which have quickly absorbed +their own secretion, begin to secrete again in the course of seven or eight +days from the time when the meat was given them. +</p> + +<p> +(3) Three minute cubes of tough cartilage from the leg-bone of a sheep were +laid on a leaf. After 10 hrs. 30 m. some acid secretion was excited, but the +cartilage appeared little or not at all affected. After 24 hrs. the cubes were +rounded and much reduced in size; after 32 hrs. they were softened to the +centre, and one was quite liquefied; after 35 hrs. mere traces of solid +cartilage were left; and after 48 hrs. a trace could still be seen through a +lens in only one of the three. After 82 hrs. not only were all three cubes +completely liquefied, but all the secretion was absorbed and the glands left +dry. +</p> + +<p> +(4) Small cubes of albumen were placed on a leaf; in 8 hrs. feebly acid +secretion extended to a distance of nearly 1/10 of an inch round them, and the +angles of one cube were rounded. After 24 hrs. the angles of all the cubes were +rounded, and they were rendered throughout very tender; after 30 hrs. the +secretion began to decrease, and after 48 hrs. the glands were left dry; but +very minute bits of albumen were still left undissolved. +</p> + +<p> +(5) Smaller cubes of albumen (about 1/50 or 1/60 of an inch, .508 or .423 mm.) +were placed on four glands; after 18 hrs. one cube was completely dissolved, +the others being much reduced in size, softened, and transparent. After 24 hrs. +two of the cubes were completely dissolved, and already the secretion on these +glands was almost wholly absorbed. After 42 hrs. the two other cubes were +completely dissolved. These four glands began to secrete again after eight or +nine days. +</p> + +<p> +(6) Two large cubes of albumen (fully 1/20 of an inch, 1.27 mm.) were placed, +one near the midrib and the other near the margin [page 383] of a leaf; in 6 +hrs. there was much secretion, which after 48 hrs. accumulated in a little pool +round the cube near the margin. This cube was much more dissolved than that on +the blade of the leaf; so that after three days it was greatly reduced in size, +with all the angles rounded, but it was too large to be wholly dissolved. The +secretion was partially absorbed after four days. The cube on the blade was +much less reduced, and the glands on which it rested began to dry after only +two days. +</p> + +<p> +(7) Fibrin excites less secretion than does meat or albumen. Several trials +were made, but I will give only three of them. Two minute shreds were placed on +some glands, and in 3 hrs. 45 m. their secretion was plainly increased. The +smaller shred of the two was completely liquefied in 6 hrs. 15 m., and the +other in 24 hrs.; but even after 48 hrs. a few granules of fibrin could still +be seen through a lens floating in both drops of secretion. After 56 hrs. 30 m. +these granules were completely dissolved. A third shred was placed in a little +pool of secretion, within the margin of a leaf where a seed had been lying, and +this was completely dissolved in the course of 15 hrs. 30 m. +</p> + +<p> +(8) Five very small bits of gluten were placed on a leaf, and they excited so +much secretion that one of the bits glided down into the marginal furrow. After +a day all five bits seemed much reduced in size, but none were wholly +dissolved. On the third day I pushed two of them, which had begun to dry, on to +fresh glands. On the fourth day undissolved traces of three out of the five +bits could still be detected, the other two having quite disappeared; but I am +doubtful whether they had really been completely dissolved. Two fresh bits were +now placed, one near the middle and the other near the margin of another leaf; +both excited an extraordinary amount of secretion; that near the margin had a +little pool formed round it, and was much more reduced in size than that on the +blade, but after four days was not completely dissolved. Gluten, therefore, +excites the glands greatly, but is dissolved with much difficulty, exactly as +in the case of Drosera. I regret that I did not try this substance after having +been immersed in weak hydrochloric acid, as it would then probably have been +quickly dissolved. +</p> + +<p> +(9) A small square thin piece of pure gelatine, moistened with water, was +placed on a leaf, and excited very little secretion in 5 hrs. 30 m., but later +in the day a greater amount. After 24 hrs. the whole square was completely +liquefied; and this would not have occurred had it been left in water. The +liquid was acid. +</p> + +<p> +(10) Small particles of chemically prepared casein excited [page 384] acid +secretion, but were not quite dissolved after two days; and the glands then +began to dry. Nor could their complete dissolution have been expected from what +we have seen with Drosera. +</p> + +<p> +(11) Minute drops of skimmed milk were placed on a leaf, and these caused the +glands to secrete freely. After 3 hrs. the milk was found curdled, and after 23 +hrs. the curds were dissolved. On placing the now clear drops under the +microscope, nothing could be detected except some oil-globules. The secretion, +therefore, dissolves fresh casein. +</p> + +<p> +(12) Two fragments of a leaf were immersed for 17 hrs., each in a drachm of a +solution of carbonate of ammonia, of two strengths, namely of one part to 437 +and 218 of water. The glands of the longer and shorter hairs were then +examined, and their contents found aggregated into granular matter of a +brownish-green colour. These granular masses were seen by my son slowly to +change their forms, and no doubt consisted of protoplasm. The aggregation was +more strongly pronounced, and the movements of the protoplasm more rapid, +within the glands subjected to the stronger solution than in the others. The +experiment was repeated with the same result; and on this occasion I observed +that the protoplasm had shrunk a little from the walls of the single elongated +cells forming the pedicels. In order to observe the process of aggregation, a +narrow strip of leaf was laid edgeways under the microscope, and the glands +were seen to be quite transparent; a little of the stronger solution (viz. one +part to 218 of water) was now added under the covering glass; after an hour or +two the glands contained very fine granular matter, which slowly became +coarsely granular and slightly opaque; but even after 5 hrs. not as yet of a +brownish tint. By this time a few rather large, transparent, globular masses +appeared within the upper ends of the pedicels, and the protoplasm lining their +walls had shrunk a little. It is thus evident that the glands of Pinguicula +absorb carbonate of ammonia; but they do not absorb it, or are not acted on by +it, nearly so quickly as those of Drosera. +</p> + +<p> +(13) Little masses of the orange-coloured pollen of the common pea, placed on +several leaves, excited the glands to secrete freely. Even a very few grains +which accidentally fell on a single gland caused the drop surrounding it to +increase so much in size, in 23 hrs., as to be manifestly larger than the drops +on the adjoining glands. Grains subjected to the secretion for 48 hrs. did not +emit their tubes; they were quite discoloured, and seemed to contain less +matter than before; that [page 385] which was left being of a dirty colour, +including globules of oil. They thus differed in appearance from other grains +kept in water for the same length of time. The glands in contact with the +pollen-grains had evidently absorbed matter from them; for they had lost their +natural pale-green tint, and contained aggregated globular masses of +protoplasm. +</p> + +<p> +(14) Square bits of the leaves of spinach, cabbage, and a saxifrage, and the +entire leaves of Erica tetralix, all excited the glands to increased secretion. +The spinach was the most effective, for it caused the secretion evidently to +increase in 1 hr. 40 m., and ultimately to run some way down the leaf; but the +glands soon began to dry, viz. after 35 hrs. The leaves of Erica tetralix began +to act in 7 hrs. 30 m., but never caused much secretion; nor did the bits of +leaf of the saxifrage, though in this case the glands continued to secrete for +seven days. Some leaves of Pinguicula were sent me from North Wales, to which +leaves of Erica tetralixand of an unknown plant adhered; and the glands in +contact with them had their contents plainly aggregated, as if they had been in +contact with insects; whilst the other glands on the same leaves contained only +clear homogeneous fluid. +</p> + +<p> +(15) Seeds.—A considerable number of seeds or fruits selected by hazard, +some fresh and some a year old, some soaked for a short time in water and some +not soaked, were tried. The ten following kinds, namely cabbage, radish, +Anemone nemorosa, Rumex acetosa, Carex sylvatica, mustard, turnip, cress, +Ranunculus acris, and Avena pubescens, all excited much secretion, which was in +several cases tested and found always acid. The five first-named seeds excited +the glands more than the others. The secretion was seldom copious until about +24 hrs. had elapsed, no doubt owing to the coats of the seeds not being easily +permeable. Nevertheless, cabbage seeds excited some secretion in 4 hrs. 30 m.; +and this increased so much in 18 hrs. as to run down the leaves. The seeds or +properly the fruits of Carex are much oftener found adhering to leaves in a +state of nature than those of any other genus; and the fruits of Carex +sylvatica excited so much secretion that in 15 hrs. it ran into the incurved +edges; but the glands ceased to secrete after 40 hrs. On the other hand, the +glands on which the seeds of the Rumex and Avena rested continued to secrete +for nine days. +</p> + +<p> +The nine following kinds of seeds excited only a slight amount of secretion, +namely, celery, parsnip, caraway, Linum grandiflorum, Cassia, Trifolium +pannonicum, Plantago, onion, [page 386] and Bromus. Most of these seeds did not +excite any secretion until 48 hrs. had elapsed, and in the case of the +Trifolium only one seed acted, and this not until the third day. Although the +seeds of the Plantago excited very little secretion, the glands continued to +secrete for six days. Lastly, the five following kinds excited no secretion, +though left on the leaves for two or three days, namely lettuce, Erica +tetralix, Atriplex hortensis, Phalaris canariensis, and wheat. Nevertheless, +when the seeds of the lettuce, wheat, and Atriplex were split open and applied +to leaves, secretion was excited in considerable quantity in 10 hrs., and I +believe that some was excited in six hours. In the case of the Atriplex the +secretion ran down to the margin, and after 24 hrs. I speak of it in my notes +“as immense in quantity and acid.” The split seeds also of the +Trifolium and celery acted powerfully and quickly, though the whole seeds +caused, as we have seen, very little secretion, and only after a long interval +of time. A slice of the common pea, which however was not tried whole, caused +secretion in 2 hrs. From these facts we may conclude that the great difference +in the degree and rate at which various kinds of seeds excite secretion, is +chiefly or wholly due to the different permeability of their coats. +</p> + +<p> +Some thin slices of the common pea, which had been previously soaked for 1 hr. +in water, were placed on a leaf, and quickly excited much acid secretion. After +24 hrs. these slices were compared under a high power with others left in water +for the same time; the latter contained so many fine granules of legumin that +the slide was rendered muddy; whereas the slices which had been subjected to +the secretion were much cleaner and more transparent, the granules of legumin +apparently having been dissolved. A cabbage seed which had lain for two days on +a leaf and had excited much acid secretion, was cut into slices, and these were +compared with those of a seed which had been left for the same time in water. +Those subjected to the secretion were of a paler colour; their coats presenting +the greatest differences, for they were of a pale dirty tint instead of +chestnut-brown. The glands on which the cabbage seeds had rested, as well as +those bathed by the surrounding secretion, differed greatly in appearance from +the other glands on the same leaf, for they all contained brownish granular +matter, proving that they had absorbed matter from the seeds. +</p> + +<p> +That the secretion acts on the seeds was also shown by some of them being +killed, or by the seedlings being injured. Fourteen cabbage seeds were left for +three days on leaves and excited [page 387] much secretion; they were then +placed on damp sand under conditions known to be favourable for germination. +Three never germinated, and this was a far larger proportion of deaths than +occurred with seeds of the same lot, which had not been subjected to the +secretion, but were otherwise treated in the same manner. Of the eleven +seedlings raised, three had the edges of their cotyledons slightly browned, as +if scorched; and the cotyledons of one grew into a curious indented shape. Two +mustard seeds germinated; but their cotyledons were marked with brown patches +and their radicles deformed. Of two radish seeds, neither germinated; whereas +of many seeds of the same lot not subjected to the secretion, all, excepting +one, germinated. Of the two Rumex seeds, one died and the other germinated; but +its radicle was brown and soon withered. Both seeds of the Avena germinated, +one grew well, the other had its radicle brown and withered. Of six seeds of +the Erica none germinated, and when cut open after having been left for five +months on damp sand, one alone seemed alive. Twenty-two seeds of various kinds +were found adhering to the leaves of plants growing in a state of nature; and +of these, though kept for five months on damp sand, none germinated, some being +then evidently dead. +</p> + +<p> +The Effects of Objects not containing Soluble Nitrogenous Matter. +</p> + +<p> +(16) It has already been shown that bits of glass, placed on leaves, excite +little or no secretion. The small amount which lay beneath the fragments was +tested and found not acid. A bit of wood excited no secretion; nor did the +several kinds of seeds of which the coats are not permeable to the secretion, +and which, therefore, acted like inorganic bodies. Cubes of fat, left for two +days on a leaf, produced no effect. +</p> + +<p> +(17) A particle of white sugar, placed on a leaf, formed in 1 hr. 10 m. a large +drop of fluid, which in the course of 2 additional hours ran down into the +naturally inflected margin. This fluid was not in the least acid, and began to +dry up, or more probably was absorbed, in 5 hrs. 30 m. The experiment was +repeated; particles being placed on a leaf, and others of the same size on a +slip of glass in a moistened state; both being covered by a bell-glass. This +was done to see whether the increased amount of fluid on the leaves could be +due to mere deliquescence; but this was proved not to be the case. The particle +on the leaf caused so much secretion that in the course of 4 hrs. it ran down +across two-thirds of the leaf. After 8 hrs. the leaf, which was concave, was +actually filled with very viscid [page 388] fluid; and it particularly deserves +notice that this, as on the former occasion, was not in the least acid. This +great amount of secretion may be attributed to exosmose. The glands which had +been covered for 24 hrs. by this fluid did not differ, when examined under the +microscope, from others on the same leaf, which had not come into contact with +it. This is an interesting fact in contrast with the invariably aggregated +condition of glands which have been bathed by the secretion, when holding +animal matter in solution. +</p> + +<p> +(18) Two particles of gum arabic were placed on a leaf, and they certainly +caused in 1 hr. 20 m. a slight increase of secretion. This continued to +increase for the next 5 hrs., that is for as long a time as the leaf was +observed. +</p> + +<p> +(19) Six small particles of dry starch of commerce were placed on a leaf, and +one of these caused some secretion in 1 hr. 15 m., and the others in from 8 +hrs. to 9 hrs. The glands which had thus been excited to secrete soon became +dry, and did not begin to secrete again until the sixth day. A larger bit of +starch was then placed on a leaf, and no secretion was excited in 5 hrs. 30 m.; +but after 8 hrs. there was a considerable supply, which increased so much in 24 +hrs. as to run down the leaf to the distance of 3/4 of an inch. This secretion, +though so abundant, was not in the least acid. As it was so copiously excited, +and as seeds not rarely adhere to the leaves of naturally growing plants, it +occurred to me that the glands might perhaps have the power of secreting a +ferment, like ptyaline, capable of dissolving starch; so I carefully observed +the above six small particles during several days, but they did not seem in the +least reduced in bulk. A particle was also left for two days in a little pool +of secretion, which had run down from a piece of spinach leaf; but although the +particle was so minute no diminution was perceptible. We may therefore conclude +that the secretion cannot dissolve starch. The increase caused by this +substance may, I presume, be attributed to exosmose. But I am surprised that +starch acted so quickly and powerfully as it did, though in a less degree than +sugar. Colloids are known to possess some slight power of dialysis; and on +placing the leaves of a Primula in water, and others in syrup and diffused +starch, those in the starch became flaccid, but to a less degree and at a much +slower rate than the leaves in the syrup; those in water remaining all the time +crisp.] +</p> + +<p> +From the foregoing experiments and observations we [page 389] see that objects +not containing soluble matter have little or no power of exciting the glands to +secrete. Non-nitrogenous fluids, if dense, cause the glands to pour forth a +large supply of viscid fluid, but this is not in the least acid. On the other +hand, the secretion from glands excited by contact with nitrogenous solids or +liquids is invariably acid, and is so copious that it often runs down the +leaves and collects within the naturally incurved margins. The secretion in +this state has the power of quickly dissolving, that is of digesting, the +muscles of insects, meat, cartilage, albumen, fibrin, gelatine, and casein as +it exists in the curds of milk. The glands are strongly excited by chemically +prepared casein and gluten; but these substances (the latter not having been +soaked in weak hydrochloric acid) are only partially dissolved, as was likewise +the case with Drosera. The secretion, when containing animal matter in +solution, whether derived from solids or from liquids, such as an infusion of +raw meat, milk, or a weak solution of carbonate of ammonia, is quickly +absorbed; and the glands, which were before limpid and of a greenish colour, +become brownish and contain masses of aggregated granular matter. This matter, +from its spontaneous movements, no doubt consists of protoplasm. No such effect +is produced by the action of non-nitrogenous fluids. After the glands have been +excited to secrete freely, they cease for a time to secrete, but begin again in +the course of a few days. +</p> + +<p> +Glands in contact with pollen, the leaves of other plants, and various kinds of +seeds, pour forth much acid secretion, and afterwards absorb matter probably of +an albuminous nature from them. Nor can the benefit thus derived be +insignificant, for a considerable [page 390] amount of pollen must be blown +from the many wind-fertilised carices, grasses, &c., growing where +Pinguicula lives, on to the leaves thickly covered with viscid glands and +forming large rosettes. Even a few grains of pollen on a single gland causes it +to secrete copiously. We have also seen how frequently the small leaves of +Erica tetralix and of other plants, as well as various kinds of seeds and +fruits, especially of Carex, adhere to the leaves. One leaf of the Pinguicula +had caught ten of the little leaves of the Erica; and three leaves on the same +plant had each caught a seed. Seeds subjected to the action of the secretion +are sometimes killed, or the seedlings injured. We may, therefore, conclude +that Pinguicula vulgaris, with its small roots, is not only supported to a +large extent by the extraordinary number of insects which it habitually +captures, but likewise draws some nourishment from the pollen, leaves, and +seeds of other plants which often adhere to its leaves. It is therefore partly +a vegetable as well as an animal feeder. +</p> + +<p class="center"> +P<small>INGUICULA GRANDIFLORA</small>. +</p> + +<p> +This species is so closely allied to the last that it is ranked by Dr. Hooker +as a sub-species. It differs chiefly in the larger size of its leaves, and in +the glandular hairs near the basal part of the midrib being longer. But it +likewise differs in constitution; I hear from Mr. Ralfs, who was so kind as to +send me plants from Cornwall, that it grows in rather different sites; and Dr. +Moore, of the Glasnevin Botanic Gardens, informs me that it is much more +manageable under culture, growing freely and flowering annually; whilst +Pinguicula vulgaris has to be renewed every year. Mr. Ralfs found numerous +[page 391] insects and fragments of insects adhering to almost all the leaves. +These consisted chiefly of Diptera, with some Hymenoptera, Homoptera, +Coleoptera, and a moth. On one leaf there were nine dead insects, besides a few +still alive. He also observed a few fruits of Carex pulicaris, as well as the +seeds of this same Pinguicula, adhering to the leaves. I tried only two +experiments with this species; firstly, a fly was placed near the margin of a +leaf, and after 16 hrs. this was found well inflected. Secondly, several small +flies were placed in a row along one margin of another leaf, and by the next +morning this whole margin was curled inwards, exactly as in the case of +Pinguicula vulgaris. +</p> + +<p class="center"> +P<small>INGUICULA LUSITANICA</small>. +</p> + +<p> +This species, of which living specimens were sent me by Mr. Ralfs from +Cornwall, is very distinct from the two foregoing ones. The leaves are rather +smaller, much more transparent, and are marked with purple branching veins. The +margins of the leaves are much more involuted; those of the older ones +extending over a third of the space between the midrib and the outside. As in +the two other species, the glandular hairs consist of longer and shorter ones, +and have the same structure; but the glands differ in being purple, and in +often containing granular matter before they have been excited. In the lower +part of the leaf, almost half the space on each side between the midrib and +margin is destitute of glands; these being replaced by long, rather stiff, +multicellular hairs, which intercross over the midrib. These hairs perhaps +serve to prevent insects from settling on this part of the leaf, where there +are no viscid glands by which they could be caught; but it is hardly probable +that they were developed for this purpose. The spiral vessels pro- [page 392] +ceeding from the midrib terminate at the extreme margin of the leaf in spiral +cells; but these are not so well developed as in the two preceding species. The +flower-peduncles, sepals, and petals, are studded with glandular hairs, like +those on the leaves. +</p> + +<p> +The leaves catch many small insects, which are found chiefly beneath the +involuted margins, probably washed there by the rain. The colour of the glands +on which insects have long lain is changed, being either brownish or pale +purple, with their contents coarsely granular; so that they evidently absorb +matter from their prey. Leaves of the Erica tetralix, flowers of a Galium, +scales of grasses, &c. likewise adhered to some of the leaves. Several of +the experiments which were tried on Pinguicula vulgaris were repeated on +Pinguicula lusitanica, and these will now be given. +</p> + +<p> +[(1) A moderately sized and angular bit of albumen was placed on one side of a +leaf, halfway between the midrib and the naturally involuted margin. In 2 hrs. +15 m. the glands poured forth much secretion, and this side became more +infolded than the opposite one. The inflection increased, and in 3 hrs. 30 m. +extended up almost to the apex. After 24 hrs. the margin was rolled into a +cylinder, the outer surface of which touched the blade of the leaf and reached +to within the 1/20 of an inch of the midrib. After 48 hrs. it began to unfold, +and in 72 hrs. was completely unfolded. The cube was rounded and greatly +reduced in size; the remainder being in a semi-liquefied state. +</p> + +<p> +(2) A moderately sized bit of albumen was placed near the apex of a leaf, under +the naturally incurved margin. In 2 hrs. 30 m. much secretion was excited, and +next morning the margin on this side was more incurved than the opposite one, +but not to so great a degree as in the last case. The margin unfolded at the +same rate as before. A large proportion of the albumen was dissolved, a remnant +being still left. +</p> + +<p> +(3) Large bits of albumen were laid in a row on the midribs of two leaves, but +produced in the course of 24 hrs. no effect; [page 393] nor could this have +been expected, for even had glands existed here, the long bristles would have +prevented the albumen from coming in contact with them. On both leaves the bits +were now pushed close to one margin, and in 3 hrs. 30 m. this became so greatly +inflected that the outer surface touched the blade; the opposite margin not +being in the least affected. After three days the margins of both leaves with +the albumen were still as much inflected as ever, and the glands were still +secreting copiously. With Pinguicula vulgaris I have never seen inflection +lasting so long. +</p> + +<p> +(4) Two cabbage seeds, after being soaked for an hour in water, were placed +near the margin of a leaf, and caused in 3 hrs. 20 m. increased secretion and +incurvation. After 24 hrs. the leaf was partially unfolded, but the glands were +still secreting freely. These began to dry in 48 hrs., and after 72 hrs. were +almost dry. The two seeds were then placed on damp sand under favourable +conditions for growth; but they never germinated, and after a time were found +rotten. They had no doubt been killed by the secretion. +</p> + +<p> +(5) Small bits of a spinach leaf caused in 1 hr. 20 m. increased secretion; and +after 3 hrs. 20 m. plain incurvation of the margin. The margin was well +inflected after 9 hrs. 15 m., but after 24 hrs. was almost fully re-expanded. +The glands in contact with the spinach became dry in 72 hrs. Bits of albumen +had been placed the day before on the opposite margin of this same leaf, as +well as on that of a leaf with cabbage seeds, and these margins remained +closely inflected for 72 hrs., showing how much more enduring is the effect of +albumen than of spinach leaves or cabbage seeds . +</p> + +<p> +(6) A row of small fragments of glass was laid along one margin of a leaf; no +effect was produced in 2 hrs. 10 m., but after 3 hrs. 25 m. there seemed to be +a trace of inflection, and this was distinct, though not strongly marked, after +6 hrs. The glands in contact with the fragments now secreted more freely than +before; so that they appear to be more easily excited by the pressure of +inorganic objects than are the glands of Pinguicula vulgaris. The above slight +inflection of the margin had not increased after 24 hrs., and the glands were +now beginning to dry. The surface of a leaf, near the midrib and towards the +base, was rubbed and scratched for some time, but no movement ensued. The long +hairs which are situated here were treated in the same manner, with no effect. +This latter trial was made because I thought that the hairs might perhaps be +sensitive to a touch, like the filaments of Dionaea. [page 394] +</p> + +<p> +(7) The flower-peduncles, sepals and petals, bear glands in general appearance +like those on the leaves. A piece of a flower-peduncle was therefore left for 1 +hr. in a solution of one part of carbonate of ammonia to 437 of water, and this +caused the glands to change from bright pink to a dull purple colour; but their +contents exhibited no distinct aggregation. After 8 hrs. 30 m. they became +colourless. Two minute cubes of albumen were placed on the glands of a +flower-peduncle, and another cube on the glands of a sepal; but they were not +excited to increased secretion, and the albumen after two days was not in the +least softened. Hence these glands apparently differ greatly in function from +those on the leaves.] +</p> + +<p> +From the foregoing observations on Pinguicula lusitanica we see that the +naturally much incurved margins of the leaves are excited to curve still +farther inwards by contact with organic and inorganic bodies; that albumen, +cabbage seeds, bits of spinach leaves, and fragments of glass, cause the glands +to secrete more freely;—that albumen is dissolved by the secretion, and +cabbage seeds killed by it;—and lastly that matter is absorbed by the +glands from the insects which are caught in large numbers by the viscid +secretion. The glands on the flower-peduncles seem to have no such power. This +species differs from Pinguicula vulgarisand grandiflora in the margins of the +leaves, when excited by organic bodies, being inflected to a greater degree, +and in the inflection lasting for a longer time. The glands, also, seem to be +more easily excited to increased secretion by bodies not yielding soluble +nitrogenous matter. In other respects, as far as my observations serve, all +three species agree in their functional powers. [page 395] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0017" id="link2HCH0017"></a> +CHAPTER XVII.<br/> +UTRICULARIA.</h2> + +<p class="letter"> +Utricularia neglecta—Structure of the bladder—The uses of the +several parts—Number of imprisoned animals—Manner of +capture—The bladders cannot digest animal matter, but absorb the products +of its decay—Experiments on the absorption of certain fluids by the +quadrifid processes—Absorption by the glands—Summary of the +observation on absorption— Development of the bladders—Utricularia +vulgaris—Utricularia minor—Utricularia clandestina. +</p> + +<p> +I was led to investigate the habits and structure of the species of this genus +partly from their belonging to the same natural family as Pinguicula, but more +especially by Mr. Holland’s statement, that “water insects are +often found imprisoned in the bladders,” which he suspects “are +destined for the plant to feed on.”* The plants which I first received as +Utricularia vulgaris from the New Forest in Hampshire and from Cornwall, and +which I have chiefly worked on, have been determined by Dr. Hooker to be a very +rare British species, the Utricularia neglecta of Lehm.** I subsequently +received the true Utricularia vulgaris from Yorkshire. Since drawing up the +following description from my own observations and those of my son, Francis +Darwin, an important memoir by Prof. Cohn +</p> + +<p class="footnote"> +* The ‘Quart. Mag. of the High Wycombe Nat. Hist. Soc.’ July 1868, +p. 5. Delpino (‘Ult. Osservaz. sulla Dicogamia,’ &c. 1868-1869, +p. 16) also quotes Crouan as having found (1858) crustaceans within the +bladders of Utricularia vulgaris. +</p> + +<p class="footnote"> +** I am much indebted to the Rev. H.M. Wilkinson, of Bistern, for having sent +me several fine lots of this species from the New Forest. Mr. Ralfs was also so +kind as to send me living plants of the same species from near Penzance in +Cornwall. [page 396] +</p> + +<p> +on Utricularia vulgaris has appeared;* and it has been no small satisfaction to +me to find that my account agrees almost completely with that of this +distinguished observer. I will publish my description as it stood before +reading that by Prof. Cohn, adding occasionally some statements on his +authority. +</p> + +<p> +FIG. 17. (Utricularia neglecta.) Branch with the divided leaves bearing +bladders; about twice enlarged. +</p> + +<p> +Utricularia neglecta.—The general appearance of a branch (about twice +enlarged), with the pinnatifid leaves bearing bladders, is represented in the +above sketch (fig. 17). The leaves continually bifurcate, so that a full-grown +one terminates in from twenty to thirty +</p> + +<p class="footnote"> +* ‘Beitrage zur Biologie der Plflanzen’ drittes Heft, 1875. [page +397] +</p> + +<p> +points. Each point is tipped by a short, straight bristle; and slight notches +on the sides of the leaves bear similar bristles. On both surfaces there are +many small papillae, crowned with two hemispherical cells in close contact. The +plants float near the surface of the water, and are quite destitute of roots, +even during the earliest period of growth.* They commonly inhabit, as more than +one observer has remarked to me, remarkably foul ditches. +</p> + +<p> +The bladders offer the chief point of interest. There are often two or three on +the same divided leaf, generally near the base; though I have seen a single one +growing from the stem. They are supported on short footstalks. When fully +grown, they are nearly 1/10 of an inch (2.54 mm.) in length. They are +translucent, of a green colour, and the walls are formed of two layers of +cells. The exterior cells are polygonal and rather large; but at many of the +points where the angles meet, there are smaller rounded cells. These latter +support short conical projections, surmounted by two hemispherical cells in +such close apposition that they appear united; but they often separate a little +when immersed in certain fluids. The papillae thus formed are exactly like +those on the surfaces of the leaves. Those on the same bladder vary much in +size; and there are a few, especially on very young bladders, which have an +elliptical instead of a circular outline. The two terminal cells are +transparent, but must hold much matter in solution, judging from the quantity +coagulated by prolonged immersion in alcohol or ether. +</p> + +<p class="footnote"> +* I infer that this is the case from a drawing of a seedling given by Dr. +Warming in his paper, “Bidrag til Kundskaben om Lentibulariaceae,” +from the ‘Videnskabelige Meddelelser,’ Copenhagen, 1874, Nos. 3-7, +pp. 33-58.) [page 398] +</p> + +<p> +The bladders are filled with water. They generally, but by no means always, +contain bubbles of air. According to the quantity of the contained water and +air, they vary much in thickness, but are always somewhat compressed. At an +early stage of growth, the flat or ventral surface faces the axis or stem; but +the footstalks must have some power of movement; for in plants kept in my +greenhouse the ventral surface was generally turned either straight or +obliquely downwards. The Rev. H.M. Wilkinson examined +</p> + +<p> +FIG. 18. (Utricularia neglecta.) Bladder; much enlarged. c, collar indistinctly +seen through the walls. +</p> + +<p> +plants for me in a state of nature, and found this commonly to be the case, but +the younger bladders often had their valves turned upwards. +</p> + +<p> +The general appearance of a bladder viewed laterally, with the appendages on +the near side alone represented, is shown in the accompanying figure (fig. 18). +The lower side, where the footstalk arises, is nearly straight, and I have +called it the ventral surface. The other or dorsal surface is convex, and +terminates in two long prolongations, formed of several rows of cells, +containing chlorophyll, and bearing, chiefly on [page 399] the outside, six or +seven long, pointed, multicellular bristles. These prolongations of the bladder +may be conveniently called the antennæ, for the whole bladder (see fig. 17) +curiously resembles an entomostracan crustacean, the short footstalk +representing the tail. In fig. 18, the near antenna alone is shown. Beneath the +two antennæ the end of the bladder is slightly truncated, and here is situated +the most important part of the whole structure, namely the entrance and valve. +On each side of the entrance from three to rarely seven long, multicellular +bristles project out- +</p> + +<p> +FIG. 19. (Utricularia neglecta.) Valve of bladder; greatly enlarged. +</p> + +<p> +wards; but only those (four in number) on the near side are shown in the +drawing. These bristles, together with those borne by the antennæ, form a sort +of hollow cone surrounding the entrance. +</p> + +<p> +The valve slopes into the cavity of the bladder, or upwards in fig. 18. It is +attached on all sides to the bladder, excepting by its posterior margin, or the +lower one in fig. 19, which is free, and forms one side of the slit-like +orifice leading into the bladder. This margin is sharp, thin, and smooth, and +rests on the edge of a rim or collar, which dips deeply into the [page 400] +bladder, as shown in the longitudinal section (fig. 20) of the collar and +valve; it is also shown at c, in fig. 18. The edge of the valve can thus open +only inwards. As both the valve and collar dip into the bladder, a hollow or +depression is here formed, at the base of which lies the slit-like orifice. +</p> + +<p> +The valve is colourless, highly transparent, flexible and elastic. It is convex +in a transverse direction, but has been drawn (fig. 19) in a flattened state, +by which its apparent breadth is increased. It is formed, +</p> + +<p> +FIG. 20. (Utricularia neglecta.) Longitudinal vertical section through the +ventral portion of a bladder; showing valve and collar. v, valve; the whole +projection above c forms the collar; b, bifid processes; s, ventral surface of +bladder. +</p> + +<p> +according to Cohn, of two layers of small cells, which are continuous with the +two layers of larger cells forming the walls of the bladder, of which it is +evidently a prolongation. Two pairs of transparent pointed bristles, about as +long as the valve itself, arise from near the free posterior margin (fig. 18), +and point obliquely outwards in the direction of the antennæ. There are also on +the surface of the valve numerous glands, as I will call them; for they have +the power of absorption, though I doubt whether they ever secrete. They consist +of three kinds, which [page 401] to a certain extent graduate into one another. +Those situated round the anterior margin of the valve (upper margin in fig. 19) +are very numerous and crowded together; they consist of an oblong head on a +long pedicel. The pedicel itself is formed of an elongated cell, surmounted by +a short one. The glands towards the free posterior margin are much larger, few +in number, and almost spherical, having short footstalks; the head is formed by +the confluence of two cells, the lower one answering to the short upper cell of +the pedicel of the oblong glands. The glands of the third kind have +transversely elongated heads, and are seated on very short footstalks; so that +they stand parallel and close to the surface of the valve; they may be called +the two-armed glands. The cells forming all these glands contain a nucleus, and +are lined by a thin layer of more or less granular protoplasm, the primordial +utricle of Mohl. They are filled with fluid, which must hold much matter in +solution, judging from the quantity coagulated after they have been long +immersed in alcohol or ether. The depression in which the valve lies is also +lined with innumerable glands; those at the sides having oblong heads and +elongated pedicels, exactly like the glands on the adjoining parts of the +valve. +</p> + +<p> +The collar (called the peristome by Cohn) is evidently formed, like the valve, +by an inward projection of the walls of the bladder. The cells composing the +outer surface, or that facing the valve, have rather thick walls, are of a +brownish colour, minute, very numerous, and elongated; the lower ones being +divided into two by vertical partitions. The whole presents a complex and +elegant appearance. The cells forming the inner surface are continuous with +those over the whole inner surface of the bladder. The space be- [page 402] +tween the inner and outer surface consists of coarse cellular tissue (fig. 20). +The inner side is thickly covered with delicate bifid processes, hereafter to +be described. The collar is thus made thick; and it is rigid, so that it +retains the same outline whether the bladder contains little or much air and +water. This is of great importance, as otherwise the thin and flexible valve +would be liable to be distorted, and in this case would not act properly. +</p> + +<p> +Altogether the entrance into the bladder, formed by the transparent valve, with +its four obliquely projecting bristles, its numerous diversely shaped glands, +surrounded by the collar, bearing glands on the inside and bristles on the +outside, together with the bristles borne by the antennæ, presents an +extraordinarily complex appearance when viewed under the microscope. +</p> + +<p> +We will now consider the internal structure of the bladder. The whole inner +surface, with the exception of the valve, is seen under a moderately high power +to be covered with a serried mass of processes (fig. 21). Each of these +consists of four divergent arms; whence their name of quadrifid processes. They +arise from small angular cells, at the junctions of the angles of the larger +cells which form the interior of the bladder. The middle part of the upper +surface of these small cells projects a little, and then contracts into a very +short and narrow footstalk which bears the four arms (fig. 22.). Of these, two +are long, but often of not quite equal length, and project obliquely inwards +and towards the posterior end of the bladder. The two others are much shorter, +and project at a smaller angle, that is, are more nearly horizontal, and are +directed towards the anterior end of the bladder. These arms are only +moderately sharp; they are composed of ex- [page 403] tremely thin transparent +membrane, so that they can be bent or doubled in any direction without being +broken. They are lined with a delicate layer of protoplasm, as is likewise the +short conical projection from which they arise. Each arm generally (but not +invariably) contains a minute, faintly brown particle, either rounded or more +commonly elongated, which exhibits incessant Brownian movements. These par- +</p> + +<p> +FIG. 21. (Utricularia neglecta.) Small portion of inside of bladder, much +enlarged, showing quadrifid processes. +</p> + +<p> +FIG. 22. (Utricularia neglecta.) One of the quadrifid processes greatly +enlarged. +</p> + +<p> +ticles slowly change their positions, and travel from one end to the other of +the arms, but are commonly found near their bases. They are present in the +quadrifids of young bladders, when only about a third of their full size. They +do not resemble ordinary nuclei, but I believe that they are nuclei in a +modified condition, for when absent, I could occasionally just distinguish in +their places a delicate halo of matter, including a darker spot. Moreover, the +quadrifids of Utricularia montana contain rather larger and much [page 404] +more regularly spherical, but otherwise similar, particles, which closely +resemble the nuclei in the cells forming the walls of the bladders. In the +present case there were sometimes two, three, or even more, nearly similar +particles within a single arm; but, as we shall hereafter see, the presence of +more than one seemed always to be connected with the absorption of decayed +matter. +</p> + +<p> +The inner side of the collar (see the previous fig. 20) is covered with several +crowded rows of processes, differing in no important respect from the +quadrifids, except in bearing only two arms instead of four; they are, however, +rather narrower and more delicate. I shall call them the bifids. They project +into the bladder, and are directed towards its posterior end. The quadrifid and +bifid processes no doubt are homologous with the papillae on the outside of the +bladder and of the leaves; and we shall see that they are developed from +closely similar papillae. +</p> + +<p> +The Uses of the several Parts.—After the above long but necessary +description of the parts, we will turn to their uses. The bladders have been +supposed by some authors to serve as floats; but branches which bore no +bladders, and others from which they had been removed, floated perfectly, owing +to the air in the intercellular spaces. Bladders containing dead and captured +animals usually include bubbles of air, but these cannot have been generated +solely by the process of decay, as I have often seen air in young, clean, and +empty bladders; and some old bladders with much decaying matter had no bubbles. +</p> + +<p> +The real use of the bladders is to capture small aquatic animals, and this they +do on a large scale. In the first lot of plants, which I received from the New +Forest early in July, a large proportion of the fully [page 405] grown bladders +contained prey; in a second lot, received in the beginning of August, most of +the bladders were empty, but plants had been selected which had grown in +unusually pure water. In the first lot, my son examined seventeen bladders, +including prey of some kind, and eight of these contained entomostracan +crustaceans, three larvæ of insects, one being still alive, and six remnants of +animals so much decayed that their nature could not be distinguished. I picked +out five bladders which seemed very full, and found in them four, five, eight, +and ten crustaceans, and in the fifth a single much elongated larva. In five +other bladders, selected from containing remains, but not appearing very full, +there were one, two, four, two, and five crustaceans. A plant of Utricularia +vulgaris, which had been kept in almost pure water, was placed by Cohn one +evening into water swarming with crustaceans, and by the next morning most of +the bladders contained these animals entrapped and swimming round and round +their prisons. They remained alive for several days; but at last perished, +asphyxiated, as I suppose, by the oxygen in the water having been all consumed. +Freshwater worms were also found by Cohn in some bladders. In all cases the +bladders with decayed remains swarmed with living Algae of many kinds, +Infusoria, and other low organisms, which evidently lived as intruders. +</p> + +<p> +Animals enter the bladders by bending inwards the posterior free edge of the +valve, which from being highly elastic shuts again instantly. As the edge is +extremely thin, and fits closely against the edge of the collar, both +projecting into the bladder (see section, fig. 20), it would evidently be very +difficult for any animal to get out when once imprisoned, and apparently they +never do escape. To show how closely the edge [page 406] fits, I may mention +that my son found a Daphnia which had inserted one of its antennæ into the +slit, and it was thus held fast during a whole day. On three or four occasions +I have seen long narrow larvæ, both dead and alive, wedged between the corner +of the valve and collar, with half their bodies within the bladder and half +out. +</p> + +<p> +As I felt much difficulty in understanding how such minute and weak animals, as +are often captured, could force their way into the bladders, I tried many +experiments to ascertain how this was effected. The free margin of the valve +bends so easily that no resistance is felt when a needle or thin bristle is +inserted. A thin human hair, fixed to a handle, and cut off so as to project +barely 1/4 of an inch, entered with some difficulty; a longer piece yielded +instead of entering. On three occasions minute particles of blue glass (so as +to be easily distinguished) were placed on valves whilst under water; and on +trying gently to move them with a needle, they disappeared so suddenly that, +not seeing what had happened, I thought that I had flirted them off; but on +examining the bladders, they were found safely enclosed. The same thing +occurred to my son, who placed little cubes of green box-wood (about 1/60 of an +inch, .423 mm.) on some valves; and thrice in the act of placing them on, or +whilst gently moving them to another spot, the valve suddenly opened and they +were engulfed. He then placed similar bits of wood on other valves, and moved +them about for some time, but they did not enter. Again, particles of blue +glass were placed by me on three valves, and extremely minute shavings of lead +on two other valves; after 1 or 2 hrs. none had entered, but in from 2 to 5 +hrs. all five were enclosed. One of the particles of glass was a [page 407] +long splinter, of which one end rested obliquely on the valve, and after a few +hours it was found fixed, half within the bladder and half projecting out, with +the edge of the valve fitting closely all round, except at one angle, where a +small open space was left. It was so firmly fixed, like the above-mentioned +larvæ, that the bladder was torn from the branch and shaken, and yet the +splinter did not fall out. My son also placed little cubes (about 1/65 of an +inch, .391 mm.) of green box-wood, which were just heavy enough to sink in +water, on three valves. These were examined after 19 hrs. 30 m., and were still +lying on the valves; but after 22 hrs. 30 m. one was found enclosed. I may here +mention that I found in a bladder on a naturally growing plant a grain of sand, +and in another bladder three grains; these must have fallen by some accident on +the valves, and then entered like the particles of glass. +</p> + +<p> +The slow bending of the valve from the weight of particles of glass and even of +box-wood, though largely supported by the water, is, I suppose, analogous to +the slow bending of colloid substances. For instance, particles of glass were +placed on various points of narrow strips of moistened gelatine, and these +yielded and became bent with extreme slowness. It is much more difficult to +understand how gently moving a particle from one part of a valve to another +causes it suddenly to open. To ascertain whether the valves were endowed with +irritability, the surfaces of several were scratched with a needle or brushed +with a fine camel-hair brush, so as to imitate the crawling movement of small +crustaceans, but the valve did not open. Some bladders, before being brushed, +were left for a time in water at temperatures between 80° and 130° F. +(26°.6-54°.4 Cent.), as, judging from a wide- [page 408] spread analogy, this +would have rendered them more sensitive to irritation, or would by itself have +excited movement; but no effect was produced. We may, therefore, conclude that +animals enter merely by forcing their way through the slit-like orifice; their +heads serving as a wedge. But I am surprised that such small and weak creatures +as are often captured (for instance, the nauplius of a crustacean, and a +tardigrade) should be strong enough to act in this manner, seeing that it was +difficult to push in one end of a bit of a hair 1/4 of an inch in length. +Nevertheless, it is certain that weak and small creatures do enter, and Mrs. +Treat, of New Jersey, has been more successful than any other observer, and has +often witnessed in the case of Utricularia clandestina the whole process.* She +saw a tardigrade slowly walking round a bladder, as if reconnoitring; at last +it crawled into the depression where the valve lies, and then easily entered. +She also witnessed the entrapment of various minute crustaceans. Cypris +“was quite wary, but nevertheless was often caught. Coming to the +entrance of a bladder, it would sometimes pause a moment, and then dash away; +at other times it would come close up, and even venture part of the way into +the entrance and back out as if afraid. Another, more heedless, would open the +door and walk in; but it was no sooner in than it manifested alarm, drew in its +feet and antennæ, and closed its shell.” Larvæ, apparently of gnats, when +“feeding near the entrance, are pretty certain to run their heads into +the net, whence there is no retreat. A large larva is sometimes three or four +hours in being swallowed, the process bringing to +</p> + +<p class="footnote"> +* ‘New York Tribune,’ reprinted in the ‘Gard. Chron.’ +1875, p. 303. [page 409] +</p> + +<p> +mind what I have witnessed when a small snake makes a large frog its +victim.” But as the valve does not appear to be in the least irritable, +the slow swallowing process must be the effect of the onward movement of the +larva. +</p> + +<p> +It is difficult to conjecture what can attract so many creatures, animal- and +vegetable-feeding crustaceans, worms, tardigrades, and various larvæ, to enter +the bladders. Mrs. Treat says that the larvæ just referred to are +vegetable-feeders, and seem to have a special liking for the long bristles +round the valve, but this taste will not account for the entrance of +animal-feeding crustaceans. Perhaps small aquatic animals habitually try to +enter every small crevice, like that between the valve and collar, in search of +food or protection. It is not probable that the remarkable transparency of the +valve is an accidental circumstance, and the spot of light thus formed may +serve as a guide. The long bristles round the entrance apparently serve for the +same purpose. I believe that this is the case, because the bladders of some +epiphytic and marsh species of Utricularia which live embedded either in +entangled vegetation or in mud, have no bristles round the entrance, and these +under such conditions would be of no service as a guide. Nevertheless, with +these epiphytic and marsh species, two pairs of bristles project from the +surface of the valve, as in the aquatic species; and their use probably is to +prevent too large animals from trying to force an entrance into the bladder, +thus rupturing orifice. +</p> + +<p> +As under favourable circumstances most of the bladders succeed in securing +prey, in one case as many as ten crustaceans;—as the valve is so well +fitted to [page 410] allow animals to enter and to prevent their +escape;—and as the inside of the bladder presents so singular a +structure, clothed with innumerable quadrifid and bifid processes, it is +impossible to doubt that the plant has been specially adapted for securing +prey. From the analogy of Pinguicula, belonging to the same family, I naturally +expected that the bladders would have digested their prey; but this is not the +case, and there are no glands fitted for secreting the proper fluid. +Nevertheless, in order to test their power of digestion, minute fragments of +roast meat, three small cubes of albumen, and three of cartilage, were pushed +through the orifice into the bladders of vigorous plants. They were left from +one day to three days and a half within, and the bladders were then cut open; +but none of the above substances exhibited the least signs of digestion or +dissolution; the angles of the cubes being as sharp as ever. These observations +were made subsequently to those on Drosera, Dionaea, Drosophyllum, and +Pinguicula; so that I was familiar with the appearance of these substances when +undergoing the early and final stages of digestion. We may therefore conclude +that Utricularia cannot digest the animals which it habitually captures. +</p> + +<p> +In most of the bladders the captured animals are so much decayed that they form +a pale brown, pulpy mass, with their chitinous coats so tender that they fall +to pieces with the greatest ease. The black pigment of the eye-spots is +preserved better than anything else. Limbs, jaws, &c. are often found quite +detached; and this I suppose is the result of the vain struggles of the later +captured animals. I have sometimes felt surprised at the small proportion of +imprisoned animals in a fresh state compared with those utterly decayed. Mrs. +Treat states with respect [page 411] to the larvæ above referred to, that +“usually in less than two days after a large one was captured the fluid +contents of the bladders began to assume a cloudy or muddy appearance, and +often became so dense that the outline of the animal was lost to view.” +This statement raises the suspicion that the bladders secrete some ferment +hastening the process of decay. There is no inherent improbability in this +supposition, considering that meat soaked for ten minutes in water mingled with +the milky juice of the papaw becomes quite tender and soon passes, as Browne +remarks in his ‘Natural History of Jamaica,’ into a state of +putridity. +</p> + +<p> +Whether or not the decay of the imprisoned animals is an any way hastened, it +is certain that matter is absorbed from them by the quadrifid and bifid +processes. The extremely delicate nature of the membrane of which these +processes are formed, and the large surface which they expose, owing to their +number crowded over the whole interior of the bladder, are circumstances all +favouring the process of absorption. Many perfectly clean bladders which had +never caught any prey were opened, and nothing could be distinguished with a +No. 8 object-glass of Hartnack within the delicate, structureless protoplasmic +lining of the arms, excepting in each a single yellowish particle or modified +nucleus. Sometimes two or even three such particles were present; but in this +case traces of decaying matter could generally be detected. On the other hand, +in bladders containing either one large or several small decayed animals, the +processes presented a widely different appearance. Six such bladders were +carefully examined; one contained an elongated, coiled-up larva; another a +single large entomostracan crustacean, and the others from two to five smaller +ones, all [page 412] in a decayed state. In these six bladders, a large number +of the quadrifid processes contained transparent, often yellowish, more or less +confluent, spherical or irregularly shaped, masses of matter. Some of the +processes, however, contained only fine granular matter, the particles of which +were so small that they could not be defined clearly with No. 8 of Hartnack. +The delicate layer of protoplasm lining their walls was in some cases a little +shrunk. On three occasions the above small masses of matter were observed and +sketched at short intervals of time; and they certainly changed their positions +relatively to each other and to the walls of the arms. Separate masses +sometimes became confluent, and then again divided. A single little mass would +send out a projection, which after a time separated itself. Hence there could +be no doubt that these masses consisted of protoplasm. Bearing in mind that +many clean bladders were examined with equal care, and that these presented no +such appearance, we may confidently believe that the protoplasm in the above +cases had been generated by the absorption of nitrogenous matter from the +decaying animals. In two or three other bladders, which at first appeared quite +clean, on careful search a few processes were found, with their outsides +clogged with a little brown matter, showing that some minute animal had been +captured and had decayed, and the arms here included a very few more or less +spherical and aggregated masses; the processes in other parts of the bladders +being empty and transparent. On the other hand, it must be stated that in three +bladders containing dead crustaceans, the processes were likewise empty. This +fact may be accounted for by the animals not having been sufficiently decayed, +or by time enough not having been allowed for the generation of proto- [page +413] plasm, or by its subsequent absorption and transference to other parts of +the plant. It will hereafter be seen that in three or four other species of +Utricularia the quadrifid processes in contact with decaying animals likewise +contained aggregated masses of protoplasm. +</p> + +<p> +On the Absorption of certain Fluids by the Quadrifid and Bifid +processes.—These experiments were tried to ascertain whether certain +fluids, which seemed adapted for the purpose, would produce the same effects on +the processes as the absorption of decayed animal matter. Such experiments are, +however, troublesome; for it is not sufficient merely to place a branch in the +fluid, as the valve shuts so closely that the fluid apparently does not enter +soon, if at all. Even when bristles were pushed into the orifices, they were in +several cases wrapped so closely round by the thin flexible edge of the valve +that the fluid was apparently excluded; so that the experiments tried in this +manner are doubtful and not worth giving. The best plan would have been to +puncture the bladders, but I did not think of this till too late, excepting in +a few cases. In all such trials, however, it cannot be ascertained positively +that the bladder, though translucent, does not contain some minute animal in +the last stage of decay. Therefore most of my experiments were made by cutting +bladders longitudinally into two; the quadrifids were examined with No. 8 of +Hartnack, then irrigated, whilst under the covering glass, with a few drops of +the fluid under trial, kept in a damp chamber, and re-examined after stated +intervals of time with the same power as before. +</p> + +<p> +[Four bladders were first tried as a control experiment, in the manner just +described, in a solution of one part of gum arabic to 218 of water, and two +bladders in a solution of one part of sugar to 437 of water; and in neither +case was any [page 414] change perceptible in the quadrifids or bifids after 21 +hrs. Four bladders were then treated in the same manner with a solution of one +part of nitrate of ammonia to 437 of water, and re-examined after 21 hrs. In +two of these the quadrifids now appeared full of very finely granular matter, +and their protoplasmic lining or primordial utricle was a little shrunk. In the +third bladder, the quadrifids included distinctly visible granules, and the +primordial utricle was a little shrunk after only 8 hrs. In the fourth bladder +the primordial utricle in most of the processes was here and there thickened +into little, irregular, yellowish specks; and from the gradations which could +be traced in this and other cases, these specks appear to give rise to the +larger free granules contained within some of the processes. Other bladders, +which, as far as could be judged, had never caught any prey, were punctured and +left in the same solution for 17 hrs.; and their quadrifids now contained very +fine granular matter. +</p> + +<p> +A bladder was bisected, examined, and irrigated with a solution of one part of +carbonate of ammonia to 437 of water. After 8 hrs. 30 m. the quadrifids +contained a good many granules, and the primordial utricle was somewhat shrunk; +after 23 hrs. the quadrifids and bifids contained many spheres of hyaline +matter, and in one arm twenty-four such spheres of moderate size were counted. +Two bisected bladders, which had been previously left for 21 hrs. in the +solution of gum (one part to 218 of water) without being affected, were +irrigated with the solution of carbonate of ammonia; and both had their +quadrifids modified in nearly the same manner as just described,—one +after only 9 hrs., and the other after 24 hrs. Two bladders which appeared +never to have caught any prey were punctured and placed in the solution; the +quadrifids of one were examined after 17 hrs., and found slightly opaque; the +quadrifids of the other, examined after 45 hrs., had their primordial utricles +more or less shrunk with thickened yellowish specks, like those due to the +action of nitrate of ammonia. Several uninjured bladders were left in the same +solution, as well as a weaker solution of one part to 1750 of water, or 1 gr. +to 4 oz.; and after two days the quadrifids were more or less opaque, with +their contents finely granular; but whether the solution had entered by the +orifice, or had been absorbed from the outside, I know not. +</p> + +<p> +Two bisected bladders were irrigated with a solution of one part of urea to 218 +of water; but when this solution was employed, I forgot that it had been kept +for some days in a warm room, and had therefore probably generated ammonia; +anyhow [page 415] the quadrifids were affected after 21 hrs. as if a solution +of carbonate of ammonia had been used; for the primordial utricle was thickened +in specks, which seemed to graduate into separate granules. Three bisected +bladders were also irrigated with a fresh solution of urea of the same +strength; their quadrifids after 21 hrs. were much less affected than in the +former case; nevertheless, the primordial utricle in some of the arms was a +little shrunk, and in others was divided into two almost symmetrical sacks. +</p> + +<p> +Three bisected bladders, after being examined, were irrigated with a putrid and +very offensive infusion of raw meat. After 23 hrs. the quadrifids and bifids in +all three specimens abounded with minute, hyaline, spherical masses; and some +of their primordial utricles were a little shrunk. Three bisected bladders were +also irrigated with a fresh infusion of raw meat; and to my surprise the +quadrifids in one of them appeared, after 23 hrs., finely granular, with their +primordial utricles somewhat shrunk and marked with thickened yellowish specks; +so that they had been acted on in the same manner as by the putrid infusion or +by the salts of ammonia. In the second bladder some of the quadrifids were +similarly acted on, though to a very slight degree; whilst the third bladder +was not at all affected.] +</p> + +<p> +From these experiments it is clear that the quadrifid and bifid processes have +the power of absorbing carbonate and nitrate of ammonia, and matter of some +kind from a putrid infusion of meat. Salts of ammonia were selected for trial, +as they are known to be rapidly generated by the decay of animal matter in the +presence of air and water, and would therefore be generated within the bladders +containing captured prey. The effect produced on the processes by these salts +and by a putrid infusion of raw meat differs from that produced by the decay of +the naturally captured animals only in the aggregated masses of protoplasm +being in the latter case of larger size; but it is probable that the fine +granules and small hyaline spheres produced by the solutions would coalesce +into larger masses, with time enough allowed. [page 416] We have seen with +Drosera that the first effect of a weak solution of carbonate of ammonia on the +cell-contents is the production of the finest granules, which afterwards +aggregate into larger, more or less rounded, masses; and that the granules in +the layer of protoplasm which flows round the walls ultimately coalesce with +these masses. Changes of this nature are, however, far more rapid in Drosera +than in Utricularia. Since the bladders have no power of digesting albumen, +cartilage, or roast meat, I was surprised that matter was absorbed, at least in +one case, from a fresh infusion of raw meat. I was also surprised, from what we +shall presently see with respect to the glands round the orifice, that a fresh +solution of urea produced only a moderate effect on the quadrifids. +</p> + +<p> +As the quadrifids are developed from papillae which at first closely resemble +those on the outside of the bladders and on the surfaces of the leaves, I may +here state that the two hemispherical cells with which these latter papillae +are crowned, and which in their natural state are perfectly transparent, +likewise absorb carbonate and nitrate of ammonia; for, after an immersion of 23 +hrs. in solutions of one part of both these salts to 437 of water, their +primordial utricles were a little shrunk and of a pale brown tint, and +sometimes finely granular. The same result followed from the immersion of a +whole branch for nearly three days in a solution of one part of the carbonate +to 1750 of water. The grains of chlorophyll, also, in the cells of the leaves +on this branch became in many places aggregated into little green masses, which +were often connected together by the finest threads. +</p> + +<p> +On the Absorption of certain Fluids by the Glands on the Valve and +Collar.—The glands round the orifices of bladders which are still young, +or which have been [page 417] long kept in moderately pure water, are +colourless; and their primordial utricles are only slightly or hardly at all +granular. But in the greater number of plants in a state of nature—and we +must remember that they generally grow in very foul water—and with plants +kept in an aquarium in foul water, most of the glands were of a pale brownish +tint; their primordial utricles were more or less shrunk, sometimes ruptured, +with their contents often coarsely granular or aggregated into little masses. +That this state of the glands is due to their having absorbed matter from the +surrounding water, I cannot doubt; for, as we shall immediately see, nearly the +same results follow from their immersion for a few hours in various solutions. +Nor is it probable that this absorption is useless, seeing that it is almost +universal with plants growing in a state of nature, excepting when the water is +remarkably pure. +</p> + +<p> +The pedicels of the glands which are situated close to the slit-like orifice, +both those on the valve and on the collar, are short; whereas the pedicels of +the more distant glands are much elongated and project inwards. The glands are +thus well placed so to be washed by any fluid coming out of the bladder through +the orifice. The valve fits so closely, judging from the result of immersing +uninjured bladders in various solutions, that it is doubtful whether any putrid +fluid habitually passes outwards. But we must remember that a bladder generally +captures several animals; and that each time a fresh animal enters, a puff of +foul water must pass out and bathe the glands. Moreover, I have repeatedly +found that, by gently pressing bladders which contained air, minute bubbles +were driven out through the orifice; and if a bladder is laid on blotting paper +and gently pressed, water oozes out. [page 418] In this latter case, as soon as +the pressure is relaxed, air is drawn in, and the bladder recovers its proper +form. If it is now placed under water and again gently pressed, minute bubbles +issue from the orifice and nowhere else, showing that the walls of the bladder +have not been ruptured. I mention this because Cohn quotes a statement by +Treviranus, that air cannot be forced out of a bladder without rupturing it. We +may therefore conclude that whenever air is secreted within a bladder already +full of water, some water will be slowly driven out through the orifice. Hence +I can hardly doubt that the numerous glands crowded round the orifice are +adapted to absorb matter from the putrid water, which will occasionally escape +from bladders including decayed animals. +</p> + +<p> +[In order to test this conclusion, I experimented with various solutions on the +glands. As in the case of the quadrifids, salts of ammonia were tried, since +these are generated by the final decay of animal matter under water. +Unfortunately the glands cannot be carefully examined whilst attached to the +bladders in their entire state. Their summits, therefore, including the valve, +collar, and antennæ, were sliced off, and the condition of the glands observed; +they were then irrigated, whilst beneath a covering glass, with the solutions, +and after a time re-examined with the same power as before, namely No. 8 of +Hartnack. The following experiments were thus made. +</p> + +<p> +As a control experiment solutions of one part of white sugar and of one part of +gum to 218 of water were first used, to see whether these produced any change +in the glands. It was also necessary to observe whether the glands were +affected by the summits of the bladders having been cut off. The summits of +four were thus tried; one being examined after 2 hrs. 30 m., and the other +three after 23 hrs.; but there was no marked change in the glands of any of +them. +</p> + +<p> +Two summits bearing quite colourless glands were irrigated with a solution of +carbonate of ammonia of the same strength (viz. one part to 218 of water) , and +in 5 m. the primordial utricles of most of the glands were somewhat contracted; +they were also thickened in specks or patches, and had assumed a pale [page +419] brown tint. When looked at again after 1 hr. 30 m., most of them presented +a somewhat different appearance. A third specimen was treated with a weaker +solution of one part of the carbonate to 437 of water, and after 1 hr. the +glands were pale brown and contained numerous granules. +</p> + +<p> +Four summits were irrigated with a solution of one part of nitrate of ammonia +to 437 of water. One was examined after 15 m., and the glands seemed affected; +after 1 hr. 10 m. there was a greater change, and the primordial utricles in +most of them were somewhat shrunk, and included many granules. In the second +specimen, the primordial utricles were considerably shrunk and brownish after 2 +hrs. Similar effects were observed in the two other specimens, but these were +not examined until 21 hrs. had elapsed. The nuclei of many of the glands +apparently had increased in size. Five bladders on a branch, which had been +kept for a long time in moderately pure water, were cut off and examined, and +their glands found very little modified. The remainder of this branch was +placed in the solution of the nitrate, and after 21 hrs. two bladders were +examined, and all their glands were brownish, with their primordial utricles +somewhat shrunk and finely granular. +</p> + +<p> +The summit of another bladder, the glands of which were in a beautifully clear +condition, was irrigated with a few drops of a mixed solution of nitrate and +phosphate of ammonia, each of one part to 437 of water. After 2 hrs. some few +of the glands were brownish. After 8 hrs. almost all the oblong glands were +brown and much more opaque than they were before; their primordial utricles +were somewhat shrunk and contained a little aggregated granular matter. The +spherical glands were still white, but their utricles were broken up into three +or four small hyaline spheres, with an irregularly contracted mass in the +middle of the basal part. These smaller spheres changed their forms in the +course of a few hours and some of them disappeared. By the next morning, after +23 hrs. 30 m., they had all disappeared, and the glands were brown; their +utricles now formed a globular shrunken mass in the middle. The utricles of the +oblong glands had shrunk very little, but their contents were somewhat +aggregated. Lastly, the summit of a bladder which had been previously irrigated +for 21 hrs. with a solution of one part of sugar to 218 of water without being +affected, was treated with the above mixed solution; and after 8 hrs. 30 m. all +the glands became brown, with their primordial utricles slightly shrunk. +</p> + +<p> +Four summits were irrigated with a putrid infusion of raw [page 420] meat. No +change in the glands was observable for some hours, but after 24 hrs. most of +them had become brownish, and more opaque and granular than they were before. +In these specimens, as in those irrigated with the salts of ammonia, the nuclei +seemed to have increased both in size and solidity, but they were not measured. +Five summits were also irrigated with a fresh infusion of raw meat; three of +these were not at all affected in 24 hrs., but the glands of the other two had +perhaps become more granular. One of the specimens which was not affected was +then irrigated with the mixed solution of the nitrate and phosphate of ammonia, +and after only 25 m. the glands contained from four or five to a dozen +granules. After six additional hours their primordial utricles were greatly +shrunk. +</p> + +<p> +The summit of a bladder was examined, and all the glands found colourless, with +their primordial utricles not at all shrunk; yet many of the oblong glands +contained granules just resolvable with No. 8 of Hartnack. It was then +irrigated with a few drops of a solution of one part of urea to 218 of water. +After 2 hrs. 25 m. the spherical glands were still colourless; whilst the +oblong and two-armed ones were of a brownish tint, and their primordial +utricles much shrunk, some containing distinctly visible granules. After 9 hrs. +some of the spherical glands were brownish, and the oblong glands were still +more changed, but they contained fewer separate granules; their nuclei, on the +other hand, appeared larger, as if they had absorbed the granules. After 23 +hrs. all the glands were brown, their primordial utricles greatly shrunk, and +in many cases ruptured. +</p> + +<p> +A bladder was now experimented on, which was already somewhat affected by the +surrounding water; for the spherical glands, though colourless, had their +primordial utricles slightly shrunk; and the oblong glands were brownish, with +their utricles much, but irregularly, shrunk. The summit was treated with the +solution of urea, but was little affected by it in 9 hrs.; nevertheless, after +23 hrs. the spherical glands were brown, with their utricles more shrunk; +several of the other glands were still browner, with their utricles contracted +into irregular little masses. +</p> + +<p> +Two other summits, with their glands colourless and their utricles not shrunk, +were treated with the same solution of urea. After 5 hrs. many of the glands +presented a shade of brown, with their utricles slightly shrunk. After 20 hrs. +40 m. some few of them were quite brown, and contained [page 421] irregularly +aggregated masses; others were still colourless, though their utricles were +shrunk; but the greater number were not much affected. This was a good instance +of how unequally the glands on the same bladder are sometimes affected, as +likewise often occurs with plants growing in foul water. Two other summits were +treated with a solution which had been kept during several days in a warm room, +and their glands were not at all affected when examined after 21 hrs. +</p> + +<p> +A weaker solution of one part of urea to 437 of water was next tried on six +summits, all carefully examined before being irrigated. The first was +re-examined after 8 hrs. 30 m., and the glands, including the spherical ones, +were brown; many of the oblong glands having their primordial utricles much +shrunk and including granules. The second summit, before being irrigated, had +been somewhat affected by the surrounding water, for the spherical glands were +not quite uniform in appearance; and a few of the oblong ones were brown, with +their utricles shrunk. Of the oblong glands, those which were before +colourless, became brown in 3 hrs. 12 m. after irrigation, with their utricles +slightly shrunk. The spherical glands did not become brown, but their contents +seemed changed in appearance, and after 23 hrs. still more changed and +granular. Most of the oblong glands were now dark brown, but their utricles +were not greatly shrunk. The four other specimens were examined after 3 hrs. 30 +m., after 4 hrs., and 9 hrs.; a brief account of their condition will be +sufficient. The spherical glands were not brown, but some of them were finely +granular. Many of the oblong glands were brown, and these, as well as others +which still remained colourless, had their utricles more or less shrunk, some +of them including small aggregated masses of matter.] +</p> + +<p> +A Summary of the Observations on Absorption.—From the facts now given +there can be no doubt that the variously shaped glands on the valve and round +the collar have the power of absorbing matter from weak solutions of certain +salts of ammonia and urea, and from a putrid infusion of raw meat. Prof. Cohn +believes that they secrete slimy matter; but I was not able to perceive any +trace of such action, excepting that, after immersion in alcohol, extremely +fine lines could sometimes be seen radiating from their [page 422] surfaces. +The glands are variously affected by absorption; they often become of a brown +colour; sometimes they contain very fine granules, or moderately sized grains, +or irregularly aggregated little masses; sometimes the nuclei appear to have +increased in size; the primordial utricles are generally more or less shrunk +and sometimes ruptured. Exactly the same changes may be observed in the glands +of plants growing and flourishing in foul water. The spherical glands are +generally affected rather differently from the oblong and two-armed ones. The +former do not so commonly become brown, and are acted on more slowly. We may +therefore infer that they differ somewhat in their natural functions. +</p> + +<p> +It is remarkable how unequally the glands on the bladders on the same branch, +and even the glands of the same kind on the same bladder, are affected by the +foul water in which the plants have grown, and by the solutions which were +employed. In the former case I presume that this is due either to little +currents bringing matter to some glands and not to others, or to unknown +differences in their constitution. When the glands on the same bladder are +differently affected by a solution, we may suspect that some of them had +previously absorbed a small amount of matter from the water. However this may +be, we have seen that the glands on the same leaf of Drosera are sometimes very +unequally affected, more especially when exposed to certain vapours. +</p> + +<p> +If glands which have already become brown, with their primordial utricles +shrunk, are irrigated with one of the effective solutions, they are not acted +on, or only slightly and slowly. If, however, a gland contains merely a few +coarse granules, this does not prevent a solution from acting. I have never +seen [page 423] any appearance making it probable that glands which have been +strongly affected by absorbing matter of any kind are capable of recovering +their pristine, colourless, and homogeneous condition, and of regaining the +power of absorbing. +</p> + +<p> +From the nature of the solutions which were tried, I presume that nitrogen is +absorbed by the glands; but the modified, brownish, more or less shrunk, and +aggregated contents of the oblong glands were never seen by me or by my son to +undergo those spontaneous changes of form characteristic of protoplasm. On the +other hand, the contents of the larger spherical glands often separated into +small hyaline globules or irregularly shaped masses, which changed their forms +very slowly and ultimately coalesced, forming a central shrunken mass. Whatever +may be the nature of the contents of the several kinds of glands, after they +have been acted on by foul water or by one of the nitrogenous solutions, it is +probable that the matter thus generated is of service to the plant, and is +ultimately transferred to other parts. +</p> + +<p> +The glands apparently absorb more quickly than do the quadrifid and bifid +processes; and on the view above maintained, namely that they absorb matter +from putrid water occasionally emitted from the bladders, they ought to act +more quickly than the processes; as these latter remain in permanent contact +with captured and decaying animals. +</p> + +<p> +Finally, the conclusion to which we are led by the foregoing experiments and +observations is that the bladders have no power of digesting animal matter, +though it appears that the quadrifids are somewhat affected by a fresh infusion +of raw meat. It is certain that the processes within the bladders, and the +glands outside, absorb matter from salts of [page 424] ammonia, from a putrid +infusion of raw meat, and from urea. The glands apparently are acted on more +strongly by a solution of urea, and less strongly by an infusion of raw meat, +than are the processes. The case of urea is particularly interesting, because +we have seen that it produces no effect on Drosera, the leaves of which are +adapted to digest fresh animal matter. But the most important fact of all is, +that in the present and following species the quadrifid and bifid processes of +bladders containing decayed animals generally include little masses of +spontaneously moving protoplasm; whilst such masses are never seen in perfectly +clean bladders. +</p> + +<p> +Development of the Bladders.—My son and I spent much time over this +subject with small success. Our observations apply to the present species and +to Utricularia vulgaris, but were made chiefly on the latter, as the bladders +are twice as large as those of Utricularia neglecta. In the early part of +autumn the stems terminate in large buds, which fall off and lie dormant during +the winter at the bottom. The young leaves forming these buds bear bladders in +various stages of early development. When the bladders of Utricularia vulgaris +are about 1/100 inch (.254 mm.) in diameter (or 1/200 in the case of +Utricularia neglecta), they are circular in outline, with a narrow, almost +closed, transverse orifice, leading into a hollow filled with water; but the +bladders are hollow when much under 1/100 of an inch in diameter. The orifices +face inwards or towards the axis of the plant. At this early age the bladders +are flattened in the plane in which the orifice lies, and therefore at right +angles to that of the mature bladders. They are covered exteriorly with +papillae of different sizes, many of which have an elliptical outline. A bundle +of vessels, formed of [page 425] simple elongated cells, runs up the short +footstalk, and divides at the base of the bladder. One branch extends up the +middle of the dorsal surface, and the other up the middle of the ventral +surface. In full-grown bladders the ventral bundle divides close beneath the +collar, and the two branches run on each side to near where the corners of the +valve unite with the collar; but these branches could not be seen in very young +bladders. +</p> + +<p> +FIG. 23. (Utricularia vulgaris.) Longitudinal section through a young bladder, +1/100 of an inch in length, with the orifice too widely open. +</p> + +<p> +The accompanying figure (fig. 23) shows a section, which happened to be +strictly medial, through the footstalk and between the nascent antennæ of a +bladder of Utricularia vulgaris, 1/100 inch in diameter. The specimen was soft, +and the young valve became separated from the collar to a greater degree than +is natural, and is thus represented. We here clearly see that the valve and +collar are infolded prolongations of the walls of the bladder. Even at this +early age, glands could be detected on the valve. The state of the quadrifid +processes will presently be described. The antennæ at this period consist of +minute cellular projections (not shown in the above figure, as they do not lie +in the medial plane), which soon bear incipient bristles. In five instances the +young antennæ were not of quite equal length; and this fact is intelligible if +I am right in believing that they represent two divisions of the leaf, rising +from the end of the bladder; for, with the true leaves, whilst very young, the +divisions are never, as far as I have seen, strictly opposite; they [page 426] +must therefore be developed one after the other, and so it would be with the +two antennæ. +</p> + +<p> +At a much earlier age, when the half formed bladders are only 1/300 inch (.0846 +mm.) in diameter or a little more, they present a totally different appearance. +One is represented on the left side of the accompanying drawing (fig. 24). The +young leaves +</p> + +<p> +FIG. 24. (Utricularia vulgaris.) Young leaf from a winter bud, showing on the +left side a bladder in its earliest stage of development. +</p> + +<p> +at this age have broad flattened segments, with their future divisions +represented by prominences, one of which is shown on the right side. Now, in a +large number of specimens examined by my son, the young bladders appeared as if +formed by the oblique folding over of the apex and of one margin with a +prominence, against the opposite margin. The circular hollow between the +infolded apex and infolded prominence apparently contracts into the narrow +orifice, wherein the valve and collar will be developed; the bladder itself +being formed by the confluence of the opposed [page 427] margins of the rest of +the leaf. But strong objections may be urged against this view, for we must in +this case suppose that the valve and collar are developed asymmetrically from +the sides of the apex and prominence. Moreover, the bundles of vascular tissue +have to be formed in lines quite irrespective of the original form of the leaf. +Until gradations can be shown to exist between this the earliest state and a +young yet perfect bladder, the case must be left doubtful. +</p> + +<p> +As the quadrifid and bifid processes offer one of the greatest peculiarities in +the genus, I carefully observed their development in Utricularia neglecta. In +bladders about 1/100 of an inch in diameter, the inner surface is studded with +papillae, rising from small cells at the junctions of the larger ones. These +papillae consist of a delicate conical protuberance, which narrows into a very +short footstalk, surmounted by two minute cells. They thus occupy the same +relative position, and closely resemble, except in being smaller and rather +more prominent, the papillae on the outside of the bladders, and on the +surfaces of the leaves. The two terminal cells of the papillae first become +much elongated in a line parallel to the inner surface of the bladder. Next, +each is divided by a longitudinal partition. Soon the two half-cells thus +formed separate from one another; and we now have four cells or an incipient +quadrifid process. As there is not space for the two new cells to increase in +breadth in their original plane, the one slides partly under the other. Their +manner of growth now changes, and their outer sides, instead of their apices, +continue to grow. The two lower cells, which have slid partly beneath the two +upper ones, form the longer and more upright pair of processes; whilst the two +upper cells form the shorter [page 428] and more horizontal pair; the four +together forming a perfect quadrifid. A trace of the primary division between +the two cells on the summits of the papillae can still be seen between the +bases of the longer processes. The development of the quadrifids is very liable +to be arrested. I have seen a bladder 1/50 of an inch in length including only +primordial papillae; and another bladder, about half its full size, with the +quadrifids in an early stage of development. +</p> + +<p> +As far as I could make out, the bifid processes are developed in the same +manner as the quadrifids, excepting that the two primary terminal cells never +become divided, and only increase in length. The glands on the valve and collar +appear at so early an age that I could not trace their development; but we may +reasonably suspect that they are developed from papillae like those on the +outside of the bladder, but with their terminal cells not divided into two. The +two segments forming the pedicels of the glands probably answer to the conical +protuberance and short footstalk of the quadrifid and bifid processes. I am +strengthened in the belief that the glands are developed from papillae like +those on the outside of the bladders, from the fact that in Utricularia +amethystina the glands extend along the whole ventral surface of the bladder +close to the footstalk. +</p> + +<p class="center"> +U<small>TRICULARIA VULGARIS</small>. +</p> + +<p> +Living plants from Yorkshire were sent me by Dr. Hooker. This species differs +from the last in the stems and leaves being thicker or coarser; their divisions +form a more acute angle with one another; the notches on the leaves bear three +or four short bristles instead of one; and the bladders are twice as large, or +about 1/5 of an inch (5.08 mm.) in diameter. In all essential respects the +bladders resemble those of Utricularia neglecta, but the sides of the peristome +are perhaps a little more [page 429] prominent, and always bear, as far as I +have seen, seven or eight long multicellular bristles. There are eleven long +bristles on each antenna, the terminal pair being included. Five bladders, +containing prey of some kind, were examined. The first included five Cypris; a +large copepod and a Diaptomus; the second, four Cypris; the third, a single +rather large crustacean; the fourth, six crustaceans; and the fifth, ten. My +son examined the quadrifid processes in a bladder containing the remains of two +crustaceans, and found some of them full of spherical or irregularly shaped +masses of matter, which were observed to move and to coalesce. These masses +therefore consisted of protoplasm. +</p> + +<p class="center"> +U<small>TRICULARIA MINOR</small>. +</p> + +<p> +FIG. 25. (Utricularia minor.) Quadrifid process, greatly enlarged. +</p> + +<p> +This rare species was sent me in a living state from Cheshire, through the +kindness of Mr. John Price. The leaves and bladders are much smaller than those +of Utricularia neglecta. The leaves bear fewer and shorter bristles, and the +bladders are more globular. The antennæ, instead of projecting in front of the +bladders, are curled under the valve, and are armed with twelve or fourteen +extremely long multicellular bristles, generally arranged in pairs. These, with +seven or eight long bristles on both sides of the peristome, form a sort of net +over the valve, which would tend to prevent all animals, excepting very small +ones, entering the bladder. The valve and collar have the same essential +structure as in the two previous species; but the glands are not quite so +numerous; the oblong ones are rather more elongated, whilst the two-armed ones +are rather less elongated. The four bristles which project obliquely from the +lower edge of the valve are short. Their shortness, compared with those on the +valves of the foregoing species, is intelligible if my view is correct that +they serve to prevent too large animals forcing an entrance through the valve, +thus injuring it; for the valve is already protected to a certain extent by the +incurved antennæ, together with the lateral bristles. The bifid processes are +like those in the previous species; but the quadrifids differ in the four arms +(fig. 25) [page 430] being directed to the same side; the two longer ones being +central, and the two shorter ones on the outside. +</p> + +<p> +The plants were collected in the middle of July; and the contents of five +bladders, which from their opacity seemed full of prey, were examined. The +first contained no less than twenty-four minute fresh-water crustaceans, most +of them consisting of empty shells, or including only a few drops of red oily +matter; the second contained twenty; the third, fifteen; the fourth, ten, some +of them being rather larger than usual; and the fifth, which seemed stuffed +quite full, contained only seven, but five of these were of unusually large +size. The prey, therefore, judging from these five bladders, consists +exclusively of fresh-water crustaceans, most of which appeared to be distinct +species from those found in the bladders of the two former species. In one +bladder the quadrifids in contact with a decaying mass contained numerous +spheres of granular matter, which slowly changed their forms and positions. +</p> + +<p class="center"> +U<small>TRICULARIA CLANDESTINA</small>. +</p> + +<p> +This North American species, which is aquatic like the three foregoing ones, +has been described by Mrs. Treat, of New Jersey, whose excellent observations +have already been largely quoted. I have not as yet seen any full description +by her of the structure of the bladder, but it appears to be lined with +quadrifid processes. A vast number of captured animals were found within the +bladders; some being crustaceans, but the greater number delicate, elongated +larvæ, I suppose of Culicidae. On some stems, “fully nine out of every +ten bladders contained these larvæ or their remains.” The larvæ +“showed signs of life from twenty-four to thirty-six hours after being +imprisoned,” and then perished. [page 431] +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2HCH0018" id="link2HCH0018"></a> +CHAPTER XVIII.<br/> +UTRICULARIA (continued).</h2> + +<p class="letter"> +Utricularia montana—Description of the bladders on the subterranean +rhizomes—Prey captured by the bladders of plants under culture and in a +state of nature—Absorption by the quadrifid processes and +glands—Tubers serving as reservoirs for water—Various other species +of Utricularia—Polypompholyx—Genlisea, different nature of the trap +for capturing prey— Diversified methods by which plants are nourished. +</p> + +<p> +FIG. 26. (Utricularia montana.) Rhizome swollen into a tuber; the branches +bearing minute bladders; of natural size. +</p> + +<p> +Utricularia montana.—This species inhabits the tropical parts of South +America, and is said to be epiphytic; but, judging from the state of the roots +(rhizomes) of some dried specimens from the herbarium at Kew, it likewise lives +in earth, probably in crevices of rocks. In English hothouses it is grown in +peaty soil. Lady Dorothy Nevill was so kind as to give me a fine plant, and I +received another from Dr. Hooker. The leaves are entire, instead of being much +divided, as in the foregoing aquatic species. They are elongated, about 1 1/2 +inch in breadth, and furnished with a distinct footstalk. The plant produces +numerous colourless rhizomes, as thin as threads, which bear minute bladders, +and occasionally swell into tubers, as will [page 432] hereafter be described. +These rhizomes appear exactly like roots, but occasionally throw up green +shoots. They penetrate the earth sometimes to the depth of more than 2 inches; +but when the plant grows as an epiphyte, they must creep amidst the mosses, +roots, decayed bark, &c., with which the trees of these countries are +thickly covered. +</p> + +<p> +As the bladders are attached to the rhizomes, they are necessarily +subterranean. They are produced in extraordinary numbers. One of my plants, +though young, must have borne several hundreds; for a single branch out of an +entangled mass had thirty-two, and another branch, about 2 inches in length +(but with its end and one side branch broken off), had seventy- three +bladders.* The bladders are compressed and rounded, with the ventral surface, +or that between the summit of the long delicate footstalk and valve, extremely +short (fig. 27). They are colourless and almost as transparent as glass, so +that they appear smaller than they really are, the largest being under the 1/20 +of an inch (1.27 mm.) in its longer diameter. They are formed of rather large +angular cells, at the junctions of which oblong papillae project, corresponding +with those on the surfaces of the bladders of the previous species. Similar +papillae abound on the rhizomes, and even on the entire leaves, but they are +rather broader on the latter. Vessels, marked with parallel bars instead of by +a spiral line, run up the footstalks, and +</p> + +<p class="footnote"> +* Prof. Oliver has figured a plant of Utricularia Jamesoniana (‘Proc. +Linn. Soc.’ vol. iv. p. 169) having entire leaves and rhizomes, like +those of our present species; but the margins of the terminal halves of some of +the leaves are converted into bladders. This fact clearly indicates that the +bladders on the rhizomes of the present and following species are modified +segments of the leaf; and they are thus brought into accordance with the +bladders attached to the divided and floating leaves of the aquatic species. +[page 433] +</p> + +<p> +just enter the bases of the bladders; but they do not bifurcate and extend up +the dorsal and ventral surfaces, as in the previous species. +</p> + +<p> +The antennæ are of moderate length, and taper to a fine point; they differ +conspicuously from those before described, in not being armed with bristles. +Their bases are so abruptly curved that their tips generally rest one on each +side of the middle of the bladder, but +</p> + +<p> +FIG. 27. (Utricularia montana.) Bladder; about 27 times enlarged. +</p> + +<p> +sometimes near the margin. Their curved bases thus form a roof over the cavity +in which the valve lies; but there is always left on each side a little +circular passage into the cavity, as may be seen in the drawing, as well as a +narrow passage between the bases of the two antennæ. As the bladders are +subterranean, had it not been for the roof, the cavity in which the valve lies +would have been liable to be blocked up with earth [page 434] and rubbish; so +that the curvature of the antennæ is a serviceable character. There are no +bristles on the outside of the collar or peristome, as in the foregoing +species. +</p> + +<p> +The valve is small and steeply inclined, with its free posterior edge abutting +against a semicircular, deeply depending collar. It is moderately transparent, +and bears two pairs of short stiff bristles, in the same position as in the +other species. The presence of these four bristles, in contrast with the +absence of those on the antennæ and collar, indicates that they are of +functional importance, namely, as I believe, to prevent too large animals +forcing an entrance through the valve. The many glands of diverse shapes +attached to the valve and round the collar in the previous species are here +absent, with the exception of about a dozen of the two-armed or transversely +elongated kind, which are seated near the borders of the valve, and are mounted +on very short footstalks. These glands are only the 3/4000 of an inch (.019 +mm.) in length; though so small, they act as absorbents. The collar is thick, +stiff, and almost semi-circular; it is formed of the same peculiar brownish +tissue as in the former species. +</p> + +<p> +The bladders are filled with water, and sometimes include bubbles of air. They +bear internally rather short, thick, quadrifid processes arranged in +approximately concentric rows. The two pairs of arms of which they are formed +differ only a little in length, and stand in a peculiar position (fig. 28); the +two longer ones forming one line, and the two shorter ones another parallel +line. Each arm includes a small spherical mass of brownish matter, which, when +crushed, breaks into angular pieces. I have no doubt that these spheres are +nuclei, for closely similar ones [page 435] are present in the cells forming +the walls of the bladders. Bifid processes, having rather short oval arms, +arise in the usual position on the inner side of the collar. +</p> + +<p> +These bladders, therefore, resemble in all essential respects the larger ones +of the foregoing species. They differ chiefly in the absence of the numerous +glands on the valve and round the collar, a few minute ones of one kind alone +being present on the valve. They differ more conspicuously in the absence of +the long bristles on the antennæ and on the outside of the collar. The presence +of these bristles in the previously mentioned species probably relates to the +capture of aquatic animals. +</p> + +<p> +FIG. 28. (Utricularia montana.) One of the quadrifid processes; much enlarged. +</p> + +<p> +It seemed to me an interesting question whether the minute bladders of +Utricularia montanaserved, as in the previous species, to capture animals +living in the earth, or in the dense vegetation covering the trees on which +this species is epiphytic; for in this case we should have a new sub-class of +carnivorous plants, namely, subterranean feeders. Many bladders, therefore, +were examined, with the following results:— +</p> + +<p> +[(1) A small bladder, less than 1/30 of an inch (.847 mm.) in diameter, +contained a minute mass of brown, much decayed matter; and in this, a tarsus +with four or five joints, terminating in a double hook, was clearly +distinguished under the microscope. I suspect that it was a remnant of one of +the Thysanoura. The quadrifids in contact with this decayed remnant contained +either small masses of translucent, yellowish matter, generally more [page 436] +or less globular, or fine granules. In distant parts of the same bladder, the +processes were transparent and quite empty, with the exception of their solid +nuclei. My son made at short intervals of time sketches of one of the above +aggregated masses, and found that they continually and completely changed their +forms; sometimes separating from one another and again coalescing. Evidently +protoplasm had been generated by the absorption of some element from the +decaying animal matter. +</p> + +<p> +(2) Another bladder included a still smaller speck of decayed brown matter, and +the adjoining quadrifids contained aggregated matter, exactly as in the last +case. +</p> + +<p> +(3) A third bladder included a larger organism, which was so much decayed that +I could only make out that it was spinose or hairy. The quadrifids in this case +were not much affected, excepting that the nuclei in the several arms differed +much in size; some of them containing two masses having a similar appearance. +</p> + +<p> +(4) A fourth bladder contained an articulate organism, for I distinctly saw the +remnant of a limb, terminating in a hook. The quadrifids were not examined. +</p> + +<p> +(5) A fifth included much decayed matter apparently of some animal, but with no +recognisable features. The quadrifids in contact contained numerous spheres of +protoplasm. +</p> + +<p> +(6) Some few bladders on the plant which I received from Kew were examined; and +in one, there was a worm-shaped animal very little decayed, with a distinct +remnant of a similar one greatly decayed. Several of the arms of the processes +in contact with these remains contained two spherical masses, like the single +solid nucleus which is properly found in each arm. In another bladder there was +a minute grain of quartz, reminding me of two similar cases with Utricularia +neglecta. +</p> + +<p> +As it appeared probable that this plant would capture a greater number of +animals in its native country than under culture, I obtained permission to +remove small portions of the rhizomes from dried specimens in the herbarium at +Kew. I did not at first find out that it was advisable to soak the rhizomes for +two or three days, and that it was necessary to open the bladders and spread +out their contents on glass; as from their state of decay and from having been +dried and pressed, their nature could not otherwise be well distinguished. +Several bladders on a plant which had grown in black earth in New Granada were +first examined; and four of these included remnants of animals. The first +contained a hairy Acarus, so much decayed that nothing was left except its +transparent coat; [page 437] also a yellow chitinous head of some animal with +an internal fork, to which the oesophagus was suspended, but I could see no +mandibles; also the double hook of the tarsus of some animal; also an elongated +greatly decayed animal; and lastly, a curious flask-shaped organism, having the +walls formed of rounded cells. Professor Claus has looked at this latter +organism, and thinks that it is the shell of a rhizopod, probably one of the +Arcellidae. In this bladder, as well as in several others, there were some +unicellular Algae, and one multicellular Alga, which no doubt had lived as +intruders. +</p> + +<p> +A second bladder contained an Acarus much less decayed than the former one, +with its eight legs preserved; as well as remnants of several other articulate +animals. A third bladder contained the end of the abdomen with the two hinder +limbs of an Acarus, as I believe. A fourth contained remnants of a distinctly +articulated bristly animal, and of several other organisms, as well as much +dark brown organic matter, the nature of which could not be made out. +</p> + +<p> +Some bladders from a plant, which had lived as an epiphyte in Trinidad, in the +West Indies, were next examined, but not so carefully as the others; nor had +they been soaked long enough. Four of them contained much brown, translucent, +granular matter, apparently organic, but with no distinguishable parts. The +quadrifids in two were brownish, with their contents granular; and it was +evident that they had absorbed matter. In a fifth bladder there was a +flask-shaped organism, like that above mentioned. A sixth contained a very +long, much decayed, worm-shaped animal. Lastly, a seventh bladder contained an +organism, but of what nature could not be distinguished.] +</p> + +<p> +Only one experiment was tried on the quadrifid processes and glands with +reference to their power of absorption. A bladder was punctured and left for 24 +hrs. in a solution of one part of urea to 437 of water, and the quadrifid and +bifid processes were found much affected. In some arms there was only a single +symmetrical globular mass, larger than the proper nucleus, and consisting of +yellowish matter, generally translucent but sometimes granular; in others there +were two masses of different sizes, one large and the [page 438] other small; +and in others there were irregularly shaped globules; so that it appeared as if +the limpid contents of the processes, owing to the absorption of matter from +the solution, had become aggregated sometimes round the nucleus, and sometimes +into separate masses; and that these then tended to coalesce. The primordial +utricle or protoplasm lining the processes was also thickened here and there +into irregular and variously shaped specks of yellowish translucent matter, as +occurred in the case of Utricularia neglecta under similar treatment. These +specks apparently did not change their forms. +</p> + +<p> +The minute two-armed glands on the valve were also affected by the solution; +for they now contained several, sometimes as many as six or eight, almost +spherical masses of translucent matter, tinged with yellow, which slowly +changed their forms and positions. Such masses were never observed in these +glands in their ordinary state. We may therefore infer that they serve for +absorption. Whenever a little water is expelled from a bladder containing +animal remains (by the means formerly specified, more especially by the +generation of bubbles of air), it will fill the cavity in which the valve lies; +and thus the glands will be able to utilise decayed matter which otherwise +would have been wasted. +</p> + +<p> +Finally, as numerous minute animals are captured by this plant in its native +country and when cultivated, there can be no doubt that the bladders, though so +small, are far from being in a rudimentary condition; on the contrary, they are +highly efficient traps. Nor can there be any doubt that matter is absorbed from +the decayed prey by the quadrifid and bifid processes, and that protoplasm is +thus generated. What tempts animals of such diverse kinds to enter [page 439] +the cavity beneath the bowed antennæ, and then force their way through the +little slit-like orifice between the valve and collar into the bladders filled +with water, I cannot conjecture. +</p> + +<p> +Tubers.—These organs, one of which is represented in a previous figure +(fig. 26) of the natural size, deserve a few remarks. Twenty were found on the +rhizomes of a single plant, but they cannot be strictly counted; for, besides +the twenty, there were all possible gradations between a short length of a +rhizome just perceptibly swollen and one so much swollen that it might be +doubtfully called a tuber. When well developed, they are oval and symmetrical, +more so than appears in the figure. The largest which I saw was 1 inch (25.4 +mm.) in length and .45 inch (11.43 mm.) in breadth. They commonly lie near the +surface, but some are buried at the depth of 2 inches. The buried ones are +dirty white, but those partly exposed to the light become greenish from the +development, of chlorophyll in their superficial cells. They terminate in a +rhizome, but this sometimes decays and drops off . They do not contain any air, +and they sink in water; their surfaces are covered with the usual papillae. The +bundle of vessels which runs up each rhizome, as soon as it enters the tuber, +separates into three distinct bundles, which reunite at the opposite end. A +rather thick slice of a tuber is almost as translucent as glass, and is seen to +consist of large angular cells, full of water and not containing starch or any +other solid matter. Some slices were left in alcohol for several days, but only +a few extremely minute granules of matter were precipitated on the walls of the +cells; and these were much smaller and fewer than those precipitated on the +cell-walls of the rhizomes and bladders. We may therefore con- [page 440] clude +that the tuber do not serve as reservoirs for food, but for water during the +dry season to which the plant is probably exposed. The many little bladders +filled with water would aid towards the same end. +</p> + +<p> +To test the correctness of this view, a small plant, growing in light peaty +earth in a pot (only 4 1/2 by 4 1/2 inches outside measure) was copiously +watered, and then kept without a drop of water in the hothouse. Two of the +upper tubers were beforehand uncovered and measured, and then loosely covered +up again. In a fortnight’s time the earth in the pot appeared extremely +dry; but not until the thirty-fifth day were the leaves in the least affected; +they then became slightly reflexed, though still soft and green. This plant, +which bore only ten tubers, would no doubt have resisted the drought for even a +longer time, had I not previously removed three of the tubers and cut off +several long rhizomes. When, on the thirty-fifth day, the earth in the pot was +turned out, it appeared as dry as the dust on a road. All the tubers had their +surfaces much wrinkled, instead of being smooth and tense. They had all shrunk, +but I cannot say accurately how much; for as they were at first symmetrically +oval, I measured only their length and thickness; but they contracted in a +transverse line much more in one direction than in another, so as to become +greatly flattened. One of the two tubers which had been measured was now +three-fourths of its original length, and two-thirds of its original thickness +in the direction in which it had been measured, but in another direction only +one- third of its former thickness. The other tuber was one-fourth shorter, +one-eighth less thick in the direction in which it had been measured, and only +half as thick in another direction. +</p> + +<p> +A slice was cut from one of these shrivelled tubers [page 441] and examined. +The cells still contained much water and no air, but they were more rounded or +less angular than before, and their walls not nearly so straight; it was +therefore clear that the cells had contracted. The tubers, as long as they +remain alive, have a strong attraction for water; the shrivelled one, from +which a slice had been cut, was left in water for 22 hrs. 30 m., and its +surface became as smooth and tense as it originally was. On the other hand, a +shrivelled tuber, which by some accident had been separated from its rhizome, +and which appeared dead, did not swell in the least, though left for several +days in water. +</p> + +<p> +With many kinds of plants, tubers, bulbs, &c. no doubt serve in part as +reservoirs for water, but I know of no case, besides the present one, of such +organs having been developed solely for this purpose. Prof. Oliver informs me +that two or three species of Utricularia are provided with these appendages; +and the group containing them has in consequence received the name of +orchidioides. All the other species of Utricularia, as well as of certain +closely related genera, are either aquatic or marsh plants; therefore, on the +principle of nearly allied plants generally having a similar constitution, a +never failing supply of water would probably be of great importance to our +present species. We can thus understand the meaning of the development of its +tubers, and of their number on the same plant, amounting in one instance to at +least twenty. +</p> + +<p class="center"> +U<small>TRICULARIA NELUMBIFOLIA, AMETHYSTINA, GRIFFITHII, CAERULEA, ORBICULATA, +MULTICAULIS</small>. +</p> + +<p> +As I wished to ascertain whether the bladders on the rhizomes of other species +of Utricularia, and of the [page 442] species of certain closely allied genera, +had the same essential structure as those of Utricularia montana, and whether +they captured prey, I asked Prof. Oliver to send me fragments from the +herbarium at Kew. He kindly selected some of the most distinct forms, having +entire leaves, and believed to inhabit marshy ground or water. My son Francis +Darwin, examined them, and has given me the following observations; but it +should be borne in mind that it is extremely difficult to make out the +structure of such minute and delicate objects after they have been dried and +pressed.* +</p> + +<p> +Utricularia nelumbifolia (Organ Mountains, Brazil).—The habitat of this +species is remarkable. According to its discoverer, Mr. Gardner,** it is +aquatic, but “is only to be found growing in the water which collects in +the bottom of the leaves of a large Tillandsia, that inhabits abundantly an +arid rocky part of the mountain, at an elevation of about 5000 feet above the +level of the sea. Besides the ordinary method by seed, it propagates itself by +runners, which it throws out from the base of the flower-stem; this runner is +always found directing itself towards the nearest Tillandsia, when it inserts +its point into the water and gives origin to a new plant, which in its turn +sends out another shoot. In this manner I have seen not less than six plants +united.” The bladders resemble those of Utricularia montana in all +essential respects, even to the presence of a few minute two-armed glands on +the valve. Within one bladder there was the remnant of the abdomen of some +larva or crustacean of large size, +</p> + +<p class="footnote"> +* Prof. Oliver has given (‘Proc. Linn. Soc.’ vol. iv. p. 169) +figures of the bladders of two South American species, namely Utricularia +Jamesoniana and peltata; but he does not appear to have paid particular +attention to these organs. +</p> + +<p class="footnote"> +** ‘Travels in the Interior of Brazil, 1836-41,’ p. 527. [page 443] +</p> + +<p> +having a brush of long sharp bristles at the apex. Other bladders included +fragments of articulate animals, and many of them contained broken pieces of a +curious organism, the nature of which was not recognised by anyone to whom it +was shown. +</p> + +<p> +Utricularia amethystina (Guiana).—This species has small entire leaves, +and is apparently a marsh plant; but it must grow in places where crustaceans +exist, for there were two small species within one of the bladders. The +bladders are nearly of the same shape as those of Utricularia montana, and are +covered outside with the usual papillae; but they differ remarkably in the +antennæ being reduced to two short points, united by a membrane hollowed out in +the middle. This membrane is covered with innumerable oblong glands supported +on long footstalks; most of which are arranged in two rows converging towards +the valve. Some, however, are seated on the margins of the membrane; and the +short ventral surface of the bladder, between the petiole and valve, is thickly +covered with glands. Most of the heads had fallen off, and the footstalks alone +remained; so that the ventral surface and the orifice, when viewed under a weak +power, appeared as if clothed with fine bristles. The valve is narrow, and +bears a few almost sessile glands. The collar against which the edge shuts is +yellowish, and presents the usual structure. From the large number of glands on +the ventral surface and round the orifice, it is probable that this species +lives in very foul water, from which it absorbs matter, as well as from its +captured and decaying prey. +</p> + +<p> +Utricularia griffithii (Malay and Borneo).—The bladders are transparent +and minute; one which was measured being only 28/1000 of an inch (.711 mm.) in +diameter. The antennæ are of moderate length, and [page 444] project straight +forward; they are united for a short space at their bases by a membrane; and +they bear a moderate number of bristles or hairs, not simple as heretofore, but +surmounted by glands. The bladders also differ remarkably from those of the +previous species, as within there are no quadrifid, only bifid, processes. In +one bladder there was a minute aquatic larva; in another the remains of some +articulate animal; and in most of them grains of sand. +</p> + +<p> +Utricularia caerulea (India).—The bladders resemble those of the last +species, both in the general character of the antennæ and in the processes +within being exclusively bifid. They contained remnants of entomostracan +crustaceans. +</p> + +<p> +Utricularia orbiculata (India).—The orbicular leaves and the stems +bearing the bladders apparently float in water. The bladders do not differ much +from those of the two last species. The antennæ, which are united for a short +distance at their bases, bear on their outer surfaces and summits numerous, +long, multicellular hairs, surmounted by glands. The processes within the +bladders are quadrifid, with the four diverging arms of equal length. The prey +which they had captured consisted of entomostracan crustaceans. +</p> + +<p> +Utricularia multicaulis (Sikkim, India, 7000 to 11,000 feet).—The +bladders, attached to rhizomes, are remarkable from the structure of the +antennæ. These are broad, flattened, and of large size; they bear on their +margins multicellular hairs, surmounted by glands. Their bases are united into +a single, rather narrow pedicel, and they thus appear like a great digitate +expansion at one end of the bladder. Internally the quadrifid processes have +divergent arms of equal length. The bladders contained remnants of articulate +animals. [page 445] +</p> + +<p class="center"> +P<small>OLYPOMPHOLYX</small>. +</p> + +<p> +This genus, which is confined to Western Australia, is characterised by having +a “quadripartite calyx.” In other respects, as Prof. Oliver +remarks,* “it is quite a Utricularia.” +</p> + +<p> +Polypompholyx multifida.—The bladders are attached in whorls round the +summits of stiff stalks. The two antennæ are represented by a minute membranous +fork, the basal part of which forms a sort of hood over the orifice. This hood +expands into two wings on each side of the bladder. A third wing or crest +appears to be formed by the extension of the dorsal surface of the petiole; but +the structure of these three wings could not be clearly made out, owing to the +state of the specimens. The inner surface of the hood is lined with long simple +hairs, containing aggregated matter, like that within the quadrifid processes +of the previously described species when in contact with decayed animals. These +hairs appear therefore to serve as absorbents. A valve was seen, but its +structure could not be determined. On the collar round the valve there are in +the place of glands numerous one-celled papillae, having very short footstalks. +The quadrifid processes have divergent arms of equal length. Remains of +entomostracan crustaceans were found within the bladders. +</p> + +<p> +Polypompholyx tenella.—The bladders are smaller than those of the last +species, but have the same general structure. They were full of dbris, +apparently organic, but no remains of articulate animals could be +distinguished. +</p> + +<p class="footnote"> +* ‘Proc. Linn. Soc.’ vol. iv. p. 171. [page 446] +</p> + +<p class="center"> +G<small>ENLISEA</small>. +</p> + +<p> +This remarkable genus is technically distinguished from Utricularia, as I hear +from Prof. Oliver, by having a five-partite calyx. Species are found in several +parts of the world, and are said to be “herbae annuae paludosae.” +</p> + +<p> +Genlisea ornata (Brazil).—This species has been described and figured by +Dr. Warming,* who states that it bears two kinds of leaves, called by him +spathulate and utriculiferous. The latter include cavities; and as these differ +much from the bladders of the foregoing species, it will be convenient to speak +of them as utricles. The accompanying figure (fig. 29) of one of the +utriculiferous leaves, about thrice enlarged, will illustrate the following +description by my son, which agrees in all essential points with that given by +Dr. Warming. The utricle (b) is formed by a slight enlargement of the narrow +blade of the leaf. A hollow neck (n), no less than fifteen times as long as the +utricle itself, forms a passage from the transverse slit-like orifice (o) into +the cavity of the utricle. A utricle which measured 1/36 of an inch (.705 mm.,) +in its longer diameter had a neck 15/36 (10.583 mm.) in length, and 1/100 of an +inch (.254 mm.) in breadth. On each side of the orifice there is a long spiral +arm or tube (a); the structure of which will be best understood by the +following illustration. Take a narrow ribbon and wind it spirally round a thin +cylinder, so that the edges come into contact along its whole length; then +pinch up the two edges so as to form a little crest, which will of course wind +spirally +</p> + +<p class="footnote"> +* “Bidrag til Kundskaben om Lentibulariaceae,” Copenhagen 1874. +[page 447] +</p> + +<p> +round the cylinder like a thread round a screw. If the cylinder is now removed, +we shall have a tube like one of the spiral arms. The two projecting edges are +not actually united, and a needle can be pushed in easily between them. They +are indeed in many places a little separated, forming narrow entrances into the +tube; but this may be the result of the drying of the specimens. The lamina of +which the tube is formed seems to be a lateral prolongation of the lip of the +orifice; and the spiral line between the two projecting edges is continuous +with the corner of the orifice. If a fine bristle is pushed down one of the +arms, it passes into the top of the hollow neck. Whether the arms are open or +closed at their extremities could not be determined, as all the specimens were +broken; nor does it appear that Dr. Warming ascertained this point. +</p> + +<p> +FIG. 29. (Genlisea ornata.) Utriculiferous leaf; enlarged about three times. l +Upper part of lamina of leaf. b Utricle or bladder. n Neck of utricle. o +Orifice. a Spirally wound arms, with their ends broken off. +</p> + +<p> +So much for the external structure. Internally the lower part of the utricle is +covered with spherical papillae, formed of four cells (sometimes eight +according to Dr. Warming), which evidently answer to the quadrifid processes +within the bladders of Utricularia. [page 448] These papillae extend a little +way up the dorsal and ventral surfaces of the utricle; and a few, according to +Warming, may be found in the upper part. This upper region is covered by many +transverse rows, one above the other, of short, closely approximate hairs, +pointing downwards. These hairs have broad bases, and their tips are formed by +a separate cell. They are absent in the lower part of the utricle where the +papillae abound. +</p> + +<p> +FIG. 30. (Genlisea ornata.) Portion of inside of neck leading into the utricle, +greatly enlarged, showing the downward pointed bristles, and small quadrifid +cells or processes. +</p> + +<p> +The neck is likewise lined throughout its whole length with transverse rows of +long, thin, transparent hairs, having broad bulbous (fig. 30) bases, with +similarly constructed sharp points. They arise from little projecting ridges, +formed of rectangular epidermic cells. The hairs vary a little in length, but +their points generally extend down to the row next below; so that if the neck +is split open and laid flat, the inner surface resembles a paper of +pins,—the hairs representing the pins, and the little transverse ridges +representing the folds of paper through which the pins are thrust. These rows +of hairs are indicated in the previous figure (29) by numerous transverse lines +crossing the neck. The inside of the neck is [page 449] also studded with +papillae; those in the lower part are spherical and formed of four cells, as in +the lower part of the utricle; those in the upper part are formed of two cells, +which are much elongated downwards beneath their points of attachment. These +two-celled papillae apparently correspond with the bifid process in the upper +part of the bladders of Utricularia. The narrow transverse orifice (o, fig. 29) +is situated between the bases of the two spiral arms. No valve could be +detected here, nor was any such structure seen by Dr. Warming. The lips of the +orifice are armed with many short, thick, sharply pointed, somewhat incurved +hairs or teeth. +</p> + +<p> +The two projecting edges of the spirally wound lamina, forming the arms, are +provided with short incurved hairs or teeth, exactly like those on the lips. +These project inwards at right angles to the spiral line of junction between +the two edges. The inner surface of the lamina supports two-celled, elongated +papillae, resembling those in the upper part of the neck, but differing +slightly from them, according to Warming, in their footstalks being formed by +prolongations of large epidermic cells; whereas the papillae within the neck +rest on small cells sunk amidst the larger ones. These spiral arms form a +conspicuous difference between the present genus and Utricularia. +</p> + +<p> +Lastly, there is a bundle of spiral vessels which, running up the lower part of +the linear leaf, divides close beneath the utricle. One branch extends up the +dorsal and the other up the ventral side of both the utricle and neck. Of these +two branches, one enters one spiral arm, and the other branch the other arm. +</p> + +<p> +The utricles contained much dbris or dirty matter, which seemed organic, though +no distinct organisms [page 450] could be recognised. It is, indeed, scarcely +possible that any object could enter the small orifice and pass down the long +narrow neck, except a living creature. Within the necks, however, of some +specimens, a worm with retracted horny jaws, the abdomen of some articulate +animal, and specks of dirt, probably the remnants of other minute creatures, +were found. Many of the papillae within both the utricles and necks were +discoloured, as if they had absorbed matter. +</p> + +<p> +From this description it is sufficiently obvious how Genlisea secures its prey. +Small animals entering the narrow orifice—but what induces them to enter +is not known any more than in the case of Utricularia—would find their +egress rendered difficult by the sharp incurved hairs on the lips, and as soon +as they passed some way down the neck, it would be scarcely possible for them +to return, owing to the many transverse rows of long, straight, downward +pointing hairs, together with the ridges from which these project. Such +creatures would, therefore, perish either within the neck or utricle; and the +quadrifid and bifid papillae would absorb matter from their decayed remains. +The transverse rows of hairs are so numerous that they seem superfluous merely +for the sake of preventing the escape of prey, and as they are thin and +delicate, they probably serve as additional absorbents, in the same manner as +the flexible bristles on the infolded margins of the leaves of Aldrovanda. The +spiral arms no doubt act as accessory traps. Until fresh leaves are examined, +it cannot be told whether the line of junction of the spirally wound lamina is +a little open along its whole course, or only in parts, but a small creature +which forced its way into the tube at any point, would be prevented from +escaping by the incurved hairs, and would find an open path down [page 451] the +tube into the neck, and so into the utricle. If the creature perished within +the spiral arms, its decaying remains would be absorbed and utilised by the +bifid papillae. We thus see that animals are captured by Genlisea, not by means +of an elastic valve, as with the foregoing species, but by a contrivance +resembling an eel-trap, though more complex. +</p> + +<p> +Genlisea africana (South Africa).—Fragments of the utriculiferous leaves +of this species exhibited the same structure as those of Genlisea ornata. A +nearly perfect Acarus was found within the utricle or neck of one leaf, but in +which of the two was not recorded. +</p> + +<p> +Genlisea aurea (Brazil).—A fragment of the neck of a utricle was lined +with transverse rows of hairs, and was furnished with elongated papillae, +exactly like those within the neck of Genlisea ornata. It is probable, +therefore, that the whole utricle is similarly constructed. +</p> + +<p> +Genlisea filiformis (Bahia, Brazil).—Many leaves were examined and none +were found provided with utricles, whereas such leaves were found without +difficulty in the three previous species. On the other hand, the rhizomes bear +bladders resembling in essential character those on the rhizomes of +Utricularia. These bladders are transparent, and very small, viz. Only 1/100 of +an inch (.254 mm.) in length. The antennæ are not united at their bases, and +apparently bear some long hairs. On the outside of the bladders there are only +a few papillae, and internally very few quadrifid processes. These latter, +however, are of unusually large size, relatively to the bladder, with the four +divergent arms of equal length. No prey could be seen within these minute +bladders. As the rhizomes of this species were furnished with bladders, those +of Genlisea africana, ornata, and aurea were carefully [page 452] examined, but +none could be found. What are we to infer from these facts? Did the three +species just named, like their close allies, the several species of +Utricularia, aboriginally possess bladders on their rhizomes, which they +afterwards lost, acquiring in their place utriculiferous leaves? In support of +this view it may be urged that the bladders of Genlisea filiformis appear from +their small size and from the fewness of their quadrifid processes to be +tending towards abortion; but why has not this species acquired utriculiferous +leaves, like its congeners? +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2H_CONC" id="link2H_CONC"></a> +CONCLUSION. </h2> + +<p> +It has now been shown that many species of Utricularia and of two closely +allied genera, inhabiting the most distant parts of the world—Europe, +Africa, India, the Malay Archipelago, Australia, North and South +America—are admirably adapted for capturing by two methods small aquatic +or terrestrial animals, and that they absorb the products of their decay. +</p> + +<p> +Ordinary plants of the higher classes procure the requisite inorganic elements +from the soil by means of their roots, and absorb carbonic acid from the +atmosphere by means of their leaves and stems. But we have seen in a previous +part of this work that there is a class of plants which digest and afterwards +absorb animal matter, namely, all the Droseraceae, Pinguicula, and, as +discovered by Dr. Hooker, Nepenthes, and to this class other species will +almost certainly soon be added. These plants can dissolve matter out of certain +vegetable substances, such as pollen, seeds, and bits of leaves. No doubt their +glands likewise absorb the salts of ammonia brought to them by the rain. It has +also been shown that some other plants can absorb ammonia by [page 453] their +glandular hairs; and these will profit by that brought to them by the rain. +There is a second class of plants which, as we have just seen, cannot digest, +but absorb the products of the decay of the animals which they capture, namely, +Utricularia and its close allies; and from the excellent observations of Dr. +Mellichamp and Dr. Canby, there can scarcely be a doubt that Sarracenia and +Darlingtonia may be added to this class, though the fact can hardly be +considered as yet fully proved. There is a third class of plants which feed, as +is now generally admitted, on the products of the decay of vegetable matter, +such as the bird’s-nest orchis (Neottia), &c. Lastly, there is the +well-known fourth class of parasites (such as the mistletoe), which are +nourished by the juices of living plants. Most, however, of the plants +belonging to these four classes obtain part of their carbon, like ordinary +species, from the atmosphere. Such are the diversified means, as far as at +present known, by which higher plants gain their subsistence. +</p> + +<hr /> + +</div><!--end chapter--> + +<div class="chapter"> + +<h2><a name="link2H_4_0022" id="link2H_4_0022"></a> +INDEX. </h2> + +<p class="center"> +A. +</p> + +<p class="noindent"> +Absorption by Dionaea, 295<br/> +— by Drosera, 17<br/> +— by Drosophyllum, 337<br/> +— by Pinguicula, 381<br/> +— by glandular hairs, 344<br/> +— by glands of Utricularia, 416, 421<br/> +— by quadrifids of Utricularia, 413, 421<br/> +— by Utricularia montana, 437 +</p> + +<p> +Acid, nature of, in digestive secretion of Drosera, 88 — present in +digestive fluid of various species of Drosera, Dionaea, Drosophyllum, and +Pinguicula, 278, 301, 339, 381 +</p> + +<p> +Acids, various, action of, on Drosera, 188 — of the acetic series +replacing hydrochloric in digestion, 89 —, arsenious and chromic, action +on Drosera, 185 —, diluted, inducing negative osmose, 197 +</p> + +<p> +Adder’s poison, action on Drosera, 206 +</p> + +<p> +Aggregation of protoplasm in Drosera, 38 — in Drosera induced by salts of +ammonia, 43 — — caused by small doses of carbonate of ammonia, 145 +— of protoplasm in Drosera, a reflex action, 242 — — in +various species of Drosera, 278 — — in Dionaea, 290, 300 +</p> + +<p> +Aggregation of protoplasm in Drosophyllum, 337, 339 — — in +Pinguicula, 370, 389 — — in Utricularia, 411, 415, 429, 430, 436 +</p> + +<p> +Albumen, digested by Drosera, 92 —, liquid, action on Drosera, 79 +</p> + +<p> +Alcohol, diluted, action of, on Drosera, 78, 216 +</p> + +<p> +Aldrovanda vesiculosa, 321 —, absorption and digestion by, 325 —, +varieties of, 329 +</p> + +<p> +Algae, aggregation in fronds of, 65 +</p> + +<p> +Alkalies, arrest digestive process in Drosera, 94 +</p> + +<p> +Aluminium, salts of, action on Drosera, 184 +</p> + +<p> +Ammonia, amount of, in rain water, 172 —, carbonate, action on heated +leaves of Drosera, 69 —, —, smallness of doses causing aggregation +in Drosera, 145 —, —, its action on Drosera, 141 —, —, +vapour of, absorbed by glands of Drosera, 142 —, —, smallness of +doses causing inflection in Drosera, 145, 168 —, phosphate, smallness of +doses causing inflection in Drosera, 153, 168 —, —, size of +particles affecting Drosera, 173 —, nitrate, smallness of doses causing +inflection in Drosera, 148, 168 —, salts of, action on Drosera, 136 +</p> + +<p> +Ammonia, salts of, their action affected by previous immersion in water and +various solutions, 213 —, —, induce aggregation in Drosera, 43 +—, various salts of, causing inflection in Drosera, 166 +</p> + +<p> +Antimony, tartrate, action on Drosera, 185 +</p> + +<p> +Areolar tissue, its digestion by Drosera, 102 +</p> + +<p> +Arsenious acid, action on Drosera, 185 +</p> + +<p> +Atropine, action on Drosera, 204 +</p> + +<p class="center"> +B. +</p> + +<p> +Barium, salts of, action on Drosera, 183 +</p> + +<p> +Bases of salts, preponderant action of, on Drosera, 186 +</p> + +<p> +Basis, fibrous, of bone, its digestion by Drosera, 108 +</p> + +<p> +Belladonna, extract of, action on Drosera, 84 +</p> + +<p> +Bennett, Mr. A.W., on Drosera, 2 —, coats of pollen-grains not digested +by insects, 117 +</p> + +<p> +Binz, on action of quinine on white blood-corpuscles, 201 —, on poisonous +action of quinine on low organisms, 202 +</p> + +<p> +Bone, its digestion by Drosera, 105 +</p> + +<p> +Brunton, Lauder, on digestion of gelatine, 111 —, on the composition of +casein, 115 —, on the digestion of urea, 124 —, — of +chlorophyll, 126 —, — of pepsin, 124 +</p> + +<p> +Byblis, 343 +</p> + +<p class="center"> +C. +</p> + +<p> +Cabbage, decoction of, action on Drosera, 83 +</p> + +<p> +Cadmium chloride, action on Drosera, 183 +</p> + +<p> +Caesium, chloride of, action on Drosera, 181 +</p> + +<p> +Calcium, salts of, action on Drosera, 182 +</p> + +<p> +Camphor, action on Drosera, 209 +</p> + +<p> +Canby, Dr., on Dionaea, 301, 310, 313 —, on Drosera filiformis, 281 +</p> + +<p> +Caraway, oil of, action on Drosera, 211 +</p> + +<p> +Carbonic acid, action on Drosera, 221 —, delays aggregation in Drosera, +59 +</p> + +<p> +Cartilage, its digestion by Drosera, 103 +</p> + +<p> +Casein, its digestion by Drosera, 114 +</p> + +<p> +Cellulose, not digested by Drosera, 125 +</p> + +<p> +Chalk, precipitated, causing inflection of Drosera, 32 +</p> + +<p> +Cheese, its digestion by Drosera, 116 +</p> + +<p> +Chitine, not digested by Drosera, 124 +</p> + +<p> +Chloroform, effects of, on Drosera, 217 —, —, on Dionaea, 304 +</p> + +<p> +Chlorophyll, grains of, in living plants, digested by Drosera, 126 —, +pure, not digested by Drosera, 125 +</p> + +<p> +Chondrin, its digestion by Drosera, 112 +</p> + +<p> +Chromic acid, action on Drosera, 185 +</p> + +<p> +Cloves, oil of, action on Drosera, 212 +</p> + +<p> +Cobalt chloride, action on Drosera, 186 +</p> + +<p> +Cobra poison, action on Drosera, 206 +</p> + +<p> +Cohn, Prof., on Aldrovanda, 321 —, on contractile tissues in plants, 364 +—, on movements of stamens of Compositae, 256 —, on Utricularia, +395 +</p> + +<p> +Colchicine, action on Drosera, 204 +</p> + +<p> +Copper chloride, action on Drosera, 185 +</p> + +<p> +Crystallin, its digestion by Drosera, 120 +</p> + +<p> +Curare, action on Drosera, 204 +</p> + +<p> +Curtis, Dr., on Dionaea, 301 +</p> + +<p class="center"> +D. +</p> + +<p> +Darwin, Francis, on the effect of an induced galvanic current on Drosera, 37 +—, on the digestion of grains of chlorophyll, 126 —, on +Utricularia, 442 +</p> + +<p> +Delpino, on Aldrovanda, 321 —, on Utricularia, 395 +</p> + +<p> +Dentine, its digestion by Drosera, 106 +</p> + +<p> +Digestion of various substances by Dionaea, 301 — — by Drosera, 85 +— — by Drosophyllum, 339 — — by Pinguicula, 381 +—, origin of power of, 361 +</p> + +<p> +Digitaline, action on Drosera, 203 +</p> + +<p> +Dionaea muscipula, small size of roots, 286 —, structure of leaves, 287 +—, sensitiveness of filaments, 289 —, absorption by, 295 —, +secretion by, 295 —, digestion by, 301 —, effects on, of +chloroform, 304 —, manner of capturing insects, 305 —, transmission +of motor impulse, 313 —, re-expansion of lobes, 318 +</p> + +<p> +Direction of inflected tentacles of Drosera, 243 +</p> + +<p> +Dohrn, Dr., on rhizocephalous crustaceans, 357 +</p> + +<p> +Donders, Prof., small amount of atropine affecting the iris of the dog, 172 +</p> + +<p> +Dragonfly caught by Drosera, 2 +</p> + +<p> +Drosera anglica, 278 — binata, vel dichotoma, 281 — capensis, 279 +— filiformis, 281 — heterophylla, 284 — intermedia, 279 +</p> + +<p> +Drosera rotundifolia, structure of leaves, 4 —, effects on, of +nitrogenous fluids, 76 Drosera rotundifolia, effects of heat on, 66 —, +its power of digestion, 85 —, backs of leaves not sensitive, 231 —, +transmission of motor impulse, 234 —, general summary, 262 — +spathulata, 280 +</p> + +<p> +Droseraceae, concluding remarks on, 355 —, their sensitiveness compared +with that of animals, 366 +</p> + +<p> +Drosophyllum, structure of leaves, 333 —, secretion by, 334 —, +absorption by, 337 —, digestion by, 339 +</p> + +<p class="center"> +E. +</p> + +<p> +Enamel, its digestion by Drosera, 106 +</p> + +<p> +Erica tetralix, glandular hairs of, 351 +</p> + +<p> +Ether, effects of, on Drosera, 219 —, —, on Dionaea, 304 +</p> + +<p> +Euphorbia, process of aggregation in roots of, 63 +</p> + +<p> +Exosmose from backs of leaves of Drosera, 231 +</p> + +<p class="center"> +F. +</p> + +<p> +Fat not digested by Drosera, 126 +</p> + +<p> +Fayrer, Dr., on the nature of cobra poison, 206 —, on the action of cobra +poison on animal protoplasm, 208 —, on cobra poison paralysing nerve +centres, 224 +</p> + +<p> +Ferment, nature of, in secretion of Drosera, 94, 97 +</p> + +<p> +Fibrin, its digestion by Drosera, 100 +</p> + +<p> +Fibro-cartilage, its digestion by Drosera, 104 +</p> + +<p> +Fibro-elastic tissue, not digested by Drosera, 122 +</p> + +<p> +Fibrous basis of bone, its digestion by Drosera, 108 +</p> + +<p> +Fluids, nitrogenous, effects of, on Drosera, 76 +</p> + +<p> +Fournier, on acids causing movements in stamens of Berberis, 196 +</p> + +<p> +Frankland, Prof., on nature of acid in secretion of Drosera, 88 +</p> + +<p class="center"> +G. +</p> + +<p> +Galvanism, current of, causing inflection of Drosera, 37 —, effects of, +on Dionaea, 318 +</p> + +<p> +Gardner, Mr., on Utricularia nelumbifolia, 442 +</p> + +<p> +Gelatin, impure, action on Drosera, 80 —, pure, its digestion by Drosera, +110 +</p> + +<p> +Genlisea africana, 451 — filiformis, 451 +</p> + +<p> +Genlisea ornata, structure of, 446 —, manner of capturing prey, 450 +</p> + +<p> +Glandular hairs, absorption by, 344 —, summary on, 353 +</p> + +<p> +Globulin, its digestion by Drosera, 120 +</p> + +<p> +Gluten, its digestion by Drosera, 117 +</p> + +<p> +Glycerine, inducing aggregation in Drosera, 52 —, action on Drosera, 212 +</p> + +<p> +Gold chloride, action on Drosera, 184 +</p> + +<p> +Gorup-Besanez on the presence of a solvent in seeds of the vetch, 362 +</p> + +<p> +Grass, decoction of, action on Drosera, 84 +</p> + +<p> +Gray, Asa, on the Droseraceae, 2 +</p> + +<p> +Groenland, on Drosera, 1, 5 +</p> + +<p> +Gum, action of, on Drosera, 77 +</p> + +<p> +Gun-cotton, not digested by Drosera, 125 +</p> + +<p class="center"> +H. +</p> + +<p> +Haematin, its digestion by Drosera, 121 +</p> + +<p> +Hairs, glandular, absorption by, 344 —, —, summary on, 353 +</p> + +<p> +Heat, inducing aggregation in Drosera, 53 —, effect of, on Drosera, 66 +—, —, on Dionaea, 294, 319 +</p> + +<p> +Heckel, on state of stamens of Berberis after excitement, 43 +</p> + +<p> +Hofmeister, on pressure arresting movements of protoplasm, 61 +</p> + +<p> +Holland, Mr., on Utricularia, 395 +</p> + +<p> +Hooker, Dr., on carnivorous plants, 2 —, on power of digestion by +Nepenthes, 97 —, history of observations on Dionaea, 286 +</p> + +<p> +Hydrocyanic acid, effects of, on Dionaea, 305 +</p> + +<p> +Hyoscyamus, action on Drosera, 84, 206 +</p> + +<p class="center"> +I. +</p> + +<p> +Iron chloride, action on Drosera, 185 +</p> + +<p> +Isinglass, solution of, action on Drosera, 80 +</p> + +<p class="center"> +J. +</p> + +<p> +Johnson, Dr., on movement of flower-stems of Pinguicula, 381 +</p> + +<p class="center"> +K. +</p> + +<p> +Klein, Dr., on microscopic character of half digested bone, 106 —, on +state of half digested fibro-cartilage, 104 —, on size of micrococci, 173 +</p> + +<p> +Knight, Mr., on feeding Dionaea, 301 +</p> + +<p> +Kossmann, Dr., on rhizocephalous crustaceans, 357 +</p> + +<p class="center"> +L. +</p> + +<p> +Lead chloride, action on Drosera, 184 +</p> + +<p> +Leaves of Drosera, backs of, not sensitive, 231 +</p> + +<p> +Legumin, its digestion by Drosera, 116 +</p> + +<p> +Lemna, aggregation in leaves of, 64 +</p> + +<p> +Lime, carbonate of, precipitated, causing inflection of Drosera, 32 —, +phosphate of, its action on Drosera, 109 +</p> + +<p> +Lithium, salts of, action on Drosera, 181 +</p> + +<p class="center"> +M. +</p> + +<p> +Magnesium, salts of, action on Drosera, 182 +</p> + +<p> +Manganese chloride, action on Drosera, 185 +</p> + +<p> +Marshall, Mr. W., on Pinguicula, 369 +</p> + +<p> +Means of movement in Dionaea, 313 — in Drosera, 254 +</p> + +<p> +Meat, infusion of, causing aggregation in Drosera, 51 —, —, action +on Drosera, 79 —, its digestion by Drosera, 98 +</p> + +<p> +Mercury perchloride, action on Drosera, 183 +</p> + +<p> +Milk, inducing aggregation in Drosera, 51 —, action on Drosera, 79 +—, its digestion by Drosera, 113 +</p> + +<p> +Mirabilis longiflora, glandular hairs of, 352 +</p> + +<p> +Moggridge, Traherne, on acids injuring seeds, 128 +</p> + +<p> +Moore, Dr., on Pinguicula, 390 +</p> + +<p> +Morphia acetate, action on Drosera, 205 +</p> + +<p> +Motor impulse in Drosera, 234, 258 — in Dionaea, 313 +</p> + +<p> +Movement, origin of power of, 363 +</p> + +<p> +Movements of leaves of Pinguicula, 371 — of tentacles of Drosera, means +of, 254 — of Dionaea, means of, 313 +</p> + +<p> +Mucin, not digested by Drosera, 122 +</p> + +<p> +Mucus, action on Drosera, 80 +</p> + +<p> +Müller, Fritz, on rhizocephalous crustaceans, 357 +</p> + +<p class="center"> +N. +</p> + +<p> +Nepenthes, its power of digestion, 97 +</p> + +<p> +Nickel chloride, action on Drosera, 186 +</p> + +<p> +Nicotiana tabacum, glandular hairs of, 352 +</p> + +<p> +Nicotine, action on Drosera, 203 +</p> + +<p> +Nitric ether, action on Drosera, 220 +</p> + +<p> +Nitschke, Dr., references to his papers on Drosera, 1 —, on sensitiveness +of backs of leaves of Drosera, 231 —, on direction of inflected tentacles +in Drosera, 244 —, on Aldrovanda, 322 +</p> + +<p> +Nourishment, various means of, by plants, 452 +</p> + +<p> +Nuttall, Dr., on re-expansion of Dionaea, 318 +</p> + +<p class="center"> +O. +</p> + +<p> +Odour of pepsin, emitted from leaves of Drosera, 88 +</p> + +<p> +Oil, olive, action of, on Drosera, 78, 126 +</p> + +<p> +Oliver, Prof., on Utricularia, 432, 441-446 +</p> + +<p class="center"> +P. +</p> + +<p> +Papaw, juice of, hastening putrefaction, 411 +</p> + +<p> +Particles, minute size of, causing inflection in Drosera, 27, 32 +</p> + +<p> +Peas, decoction of, action on Drosera, 82 +</p> + +<p> +Pelargonium zonale, glandular hairs of, 350 +</p> + +<p> +Pepsin, odour of, emitted from Drosera leaves, 88 —, not digested by +Drosera, 123 —, its secretion by animals excited only after absorption, +129 +</p> + +<p> +Peptogenes, 129 +</p> + +<p> +Pinguicula grandiflora, 390 — lusitanica, 391 +</p> + +<p> +Pinguicula vulgaris, structure of leaves and roots, 368 —, number of +insects caught by, 369 —, power of movement, 371 —, secretion and +absorption by, 381 —, digestion by, 381 —, effects of secretion on +living seeds, 390 +</p> + +<p> +Platinum chloride, action on Drosera, 186 +</p> + +<p> +Poison of cobra and adder, their action on Drosera, 206 +</p> + +<p> +Pollen, its digestion by Drosera, 117 +</p> + +<p> +Polypompholyx, structure of, 445 +</p> + +<p> +Potassium, salts of, inducing aggregation in Drosera, 50 —, —, +action on Drosera, 179 — phosphate, not decomposed by Drosera, 180, 187 +</p> + +<p> +Price, Mr. John, on Utricularia, 429 +</p> + +<p> +Primula sinensis, glandular hairs of, 348 —, number of glandular hairs +of, 355 +</p> + +<p> +Protoplasm, aggregation of, in Drosera, 38 —, —, in Drosera, caused +by small doses of carbonate of ammonia, 145 —, —, in Drosera, a +reflex action, 242 — aggregated, re-dissolution of, 53 —, +aggregation of, in various species of Drosera, 278 —, —, in +Dionaea, 290, 300 —, —, in Drosophyllum, 337, 339 —, —, +in Pinguicula, 370, 389 —, —, in Utricularia, 411, 415, 429, 430, +436 +</p> + +<p class="center"> +Q. +</p> + +<p> +Quinine, salts of, action on Drosera, 201 +</p> + +<p class="center"> +R. +</p> + +<p> +Rain-water, amount of ammonia in, 172 +</p> + +<p> +Ralfs, Mr., on Pinguicula, 390 +</p> + +<p> +Ransom, Dr., action of poisons on the yolk of eggs, 225 +</p> + +<p> +Re-expansion of headless tentacles of Drosera, 229 — of tentacles of +Drosera, 260 — of Dionaea, 318 +</p> + +<p> +Roots of Drosera, 18 — of Drosera, process of aggregation in, 63 — +of Drosera, absorb carbonate of ammonia, 141 — of Dionaea, 286 — of +Drosophyllum, 332 — of Pinguicula, 369 +</p> + +<p> +Roridula, 342 +</p> + +<p> +Rubidium chloride, action on Drosera, 181 +</p> + +<p class="center"> +S. +</p> + +<p> +Sachs, Prof., effects of heat on protoplasm, 66, 70 —, on the dissolution +of proteid compounds in the tissues of plants, 362 +</p> + +<p> +Saliva, action on Drosera, 80 +</p> + +<p> +Salts and acids, various, effects of, on subsequent action of ammonia, 214 +</p> + +<p> +Sanderson, Burdon, on coagulation of albumen from heat, 74 —, on acids +replacing hydrochloric in digestion, 89 —, on the digestion of fibrous +basis of bone, 108 —, — of gluten, 118 —, — of +globulin, 120 —, — of chlorophyll, 126 —, on different effect +of sodium and potassium on animals, 187 —, on electric currents in +Dionaea, 318 +</p> + +<p> +Saxifraga umbrosa, glandular hairs of, 345 +</p> + +<p> +Schiff, on hydrochloric acid dissolving coagulated albumen, 86 —, on +manner of digestion of albumen, 93 —, on changes in meat during +digestion, 99 —, on the coagulation of milk, 114 —, on the +digestion of casein, 116 —, — of mucus, 123 —, on peptogenes, +129 +</p> + +<p> +Schloesing, on absorption of nitrogen by Nicotiana, 352 +</p> + +<p> +Scott, Mr., on Drosera, 1 +</p> + +<p> +Secretion of Drosera, general account of, 13 — —, its antiseptic +power, 15 — —, becomes acid from excitement, 86 — —, +nature of its ferment, 94, 97 — by Dionaea, 295 — by Drosophyllum, +335 — by Pinguicula, 381 +</p> + +<p> +Seeds, living, acted on by Drosera, 127 —, —, acted on by +Pinguicula, 385, 390 +</p> + +<p> +Sensitiveness, localisation of, in Drosera, 229 — of Dionaea, 289 — +of Pinguicula, 371 +</p> + +<p> +Silver nitrate, action on Drosera, 181 +</p> + +<p> +Sodium, salts of, action on Drosera, 176 —, —, inducing aggregation +in Drosera, 50 +</p> + +<p> +Sondera heterophylla, 284 +</p> + +<p> +Sorby, Mr., on colouring matter of Drosera, 5 +</p> + +<p> +Spectroscope, its power compared with that of Drosera, 170 +</p> + +<p> +Starch, action of, on Drosera, 78, 126 +</p> + +<p> +Stein, on Aldrovanda, 321 +</p> + +<p> +Strontium, salts of, action on Drosera, 183 +</p> + +<p> +Strychnine, salts of, action on Drosera, 199 +</p> + +<p> +Sugar, solution of, action of, on Drosera, 78 —, —, inducing +aggregation in Drosera, 51 +</p> + +<p> +Sulphuric ether, action on Drosera, 219 —, — on Dionaea, 304 +</p> + +<p> +Syntonin, its action on Drosera, 102 +</p> + +<p class="center"> +T. +</p> + +<p> +Tait, Mr., on Drosophyllum, 332 +</p> + +<p> +Taylor, Alfred, on the detection of minute doses of poisons, 170 +</p> + +<p> +Tea, infusion of, action on Drosera, 78 +</p> + +<p> +Tentacles of Drosera, move when glands cut of, 36, 229 —, inflection, +direction of, 243 —, means of movement, 254 —, re-expansion of, 260 +</p> + +<p> +Theine, action on Drosera, 204 +</p> + +<p> +Tin chloride, action on Drosera, 185 +</p> + +<p> +Tissue, areolar, its digestion by Drosera, 102 —, fibro-elastic, not +digested by Drosera, 122 +</p> + +<p> +Tissues through which impulse is transmitted in Drosera, 247 — — in +Dionaea, 313 +</p> + +<p> +Touches repeated, causing inflection in Drosera, 34 +</p> + +<p> +Transmission of motor impulse in Drosera, 234 — — in Dionaea, 313 +</p> + +<p> +Traube, Dr., on artificial cells, 216 +</p> + +<p> +Treat, Mrs., on Drosera filiformis, 281 —, on Dionaea, 311 —, on +Utricularia, 408, 430 +</p> + +<p> +Trcul, on Drosera, 1, 5 +</p> + +<p> +Tubers of Utricularia montana, 439 +</p> + +<p> +Turpentine, action on Drosera, 212 +</p> + +<p class="center"> +U. +</p> + +<p> +Urea, not digested by Drosera, 124 +</p> + +<p> +Urine, action on Drosera, 79 +</p> + +<p> +Utricularia clandestina, 430 — minor, 429 +</p> + +<p> +Utricularia montana, structure of bladders, 431 —, animals caught by, 435 +—, absorption by, 437 —, tubers of, serving as reservoirs, 439 +</p> + +<p> +Utricularia neglecta, structure of bladders, 397 —, animals caught by, +405 —, absorption by, 413 —, summary on absorption, 421 —, +development of bladders, 424 +</p> + +<p> +Utricularia, various species of, 441 +</p> + +<p> +Utricularia vulgaris, 428 +</p> + +<p class="center"> +V. +</p> + +<p> +Veratrine, action on Drosera, 204 +</p> + +<p> +Vessels in leaves of Drosera, 247 — of Dionaea, 314 +</p> + +<p> +Vogel, on effects of camphor on plants, 209 +</p> + +<p class="center"> +W. +</p> + +<p> +Warming, Dr., on Drosera, 2, 6 —, on roots of Utricularia, 397 —, +on trichomes, 359 —, on Genlisea, 446 —, on parenchymatous cells in +tentacles of Drosera, 252 +</p> + +<p> +Water, drops of, not causing inflection in Drosera, 35 —, its power in +causing aggregation in Drosera, 52 —, its power in causing inflection in +Drosera, 139 — and various solutions, effects of, on subsequent action of +ammonia, 213 +</p> + +<p> +Wilkinson, Rev., on Utricularia, 398 +</p> + +<p class="center"> +Z. +</p> + +<p> +Ziegler, his statements with respect to Drosera, 23 —, experiments by +cutting vessels of Drosera, 249 +</p> + +<p> +Zinc chloride, action on Drosera, 184 +</p> + +</div><!--end chapter--> + +<div style='display:block; margin-top:4em'>*** END OF THE PROJECT GUTENBERG EBOOK INSECTIVOROUS PLANTS ***</div> +<div style='text-align:left'> + +<div style='display:block; margin:1em 0'> +Updated editions will replace the previous one—the old editions will +be renamed. +</div> + +<div style='display:block; margin:1em 0'> +Creating the works from print editions not protected by U.S. copyright +law means that no one owns a United States copyright in these works, +so the Foundation (and you!) can copy and distribute it in the United +States without permission and without paying copyright +royalties. 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