Insectivorous Plants

It seems at first sight a probable view that aggrega- tion 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 gener- ally* or, as I believe, always, secrete more copiously than they did before. Again, during the re-expansion

of the tentacles, the glands secrete less freely, or quite cease to secrete, and the aggregated masses of proto- plasm are then redissolved. Moreover, when leaves are immersed in dense vegetable solutions, or in glycerine, the fluid within the gland-cells passes out- wards, 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. 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 aggre- gation. Thus a particle of sugar added to the secre- tion 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 samo 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 tempe- rature 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 rn. 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 pa- pill?e, described in the first chapter, with which the

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 sensi- tive filaments of Dionasa, which do not secrete, like- wise undergoes aggregation from the action of a weak solution of carbonate of ammonia.

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

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. 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. (4S°'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° (650>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° (620>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.

Tbe fluid within the cells of the tentacles must be in an oxygenated condition, in order that the force of influence which induces aggregation should bo trans- mitted 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 in- stantly blackened, showing that they had absorbed, and that their contents were aggregated; but in the cells close beneath the glands there was no aggre- gation 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 aggre- gation 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 solu- tion 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 be- neath 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

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 in. 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.

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 pro- cess 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

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 car- bonate 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 redis- solved, and the cells become filled with homogeneous purple fluid, as they were at first. The process of re- dissolution commences at the bases of the tentacles, thence proceeding upwards to the glands ; and, there- fore, in a reversed direction to that of aggregation.

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 * According to Hofmeister (as gation is a different phenomenon, quoted by Sachs, ' Traite de Bot." as it relates to the contents of the

sure on the cell-membrane arrests layer of protoplasm which flows immediately the movements of along the walls ; though no doubt the protoplasm, and even deter- the effects of pressure or of :i walls. But the process of aggre- transmitted through this layer. the glands, — by the glands absorbing various fluids or matter dissolved out of certain bodies, — by exosrnose, — and by a certain degree of heat. On the other hand, a temperature of about 150° Fahr. (650<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 con- clude 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 oxygen- ated state, in order that the process of aggregation should travel from cell to cell at the proper rate.

Various nitrogenous organic fluids and salts of am- monia induce aggregation, but in different degrees and at very different rates. Carbonate of ammonia is the most powerful of all known substances ; the ab- sorption of -rg-rVo-o °f a grain (-000482 nig.) 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 nrcich 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

any aggregation. Nevertheless, before being thug affected, they are able, at least in some cases, to excite aggregation in their own tentacles. That the central glands, if irritated, send centri- fugally 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 aggrega- tion 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.

Supplementary Observations on the Process of Aggre- gation in the Hoots of Plants. It will hereafter be seen that a weak solution ol the tvu- bonate 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 1 met with, viz. Euphorbia peplus, being care- 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 appear- ance, 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 experi- ment 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 J 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. Boots 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.

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.

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 l£ 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£ 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 o>

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. A green marine alga was left for some time in this same solu- tion, 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.

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. IN my observations on Drosera rotundifoUa, the leaves seemed to be more quickly inflected over animal sub- stances, 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 pre- sented itself, namely, at what degree life was extin- guished ; 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 espe- cially in the failure of the protoplasm to become aggregated, when the leaves after being heated are immersed in a solution of carbonate of ammonia.*

* When my experiments on the eludes that the protoplasm with- effects of heat were made, I was in their cells always coagulates, not aware that the subject had if in a damp condition, at a tern- been carefully investigated by perature of between 50° and 60° several observers. For instance, Cent., or 122° to 140° Fahr. Max Sachs is convinced (.' Traite' de Schultze and Kiihne (as quoted Botauique,' 1874, pp. 772, 854) by Dr. Bastian in 'Contemp. that the most different kinds of Review,' 1874, p. 528) " found plants all perish if kept for 10m. that the protoplasm of plant- in water at 45° to 4t>° Cent., or cells, with which they experi- 113° to 115° Fahr. ; and he con- mented, was always killed aud

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 ten- tacles 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 car- bonate 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.

It will be convenient first briefly to describe tb.3 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

altered by a very brief expo- able differences in this respect is enre to a temperature of 118£° not surprising, considering that results are deduced from special grow in hot springs — cases of quent aggregation of the proto- Prof. Wyman (' American Journal the tentacles, they seem to me Dr. Hooker found Confervse in worth giving. We shall find that water at 1 (J8° Fahr. ; Humboldt, Drosera resists heat somewhat at 185° Fahr. ; and Descloizeaux, better than most other plants. at 208° Fahr. That there should be consider-

when the leaves are subsequently placed in a solution of car- bonate 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. 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. (430-3 Cent.); a leaf being taken out as soon as the temperature rose to 80° (2G°'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 110° 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, there- fore, that the warm bath had increased their sensitiveness when excited by meat.

I next observed the degree of inflection which leaves under- went 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° (87°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° (430-3 Cent.), was somewhat in- flected in 4 m., and considerably so in from 6 m. to 7 m.

Three leaves were placed in water which was heated rather quickly, and by the time the temperature rose to 115°— 116° (46°'l to 460-06 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 100° (37°7 Cent.), which was raised to 120° (480>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 follow- ing morning it was immersed in a weak solution of carbonate of

ammonia, and the glands quickly became black, with strongly marked aggregation in the tentacles, showing that the proto- plasm was alive, and that the glands had not lost their power of absorption. Another leaf was placed in water at 110° (43°'3 Cent.) which was raised to 120° (4S°'8 Cent.) ; and every ten- tacle, excepting one, was quickly and closely inflected. This leaf was now immersed in a few drops of a strong solution of car- bonate 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 proto- plasm did not become spherical, as almost always occurs with leaves immersed in a solution of carbonate of ammonia.

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° (540>4 Cent.) is too high to cause immediate inflection, yet does not kill the leaves. 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

distinctly seen in a small mass of protoplasm in one of the cells of a tentacle.* After a few hours all the tentacles and thf blade became inflected. Experiment 2. — Another leaf was plunged into water at 130'" to 131°, and as before there was no inflection. After being kepf in cold water for an hour, it was placed in the strong solutior of ammonia, and in the course of 55 m. the tentacles were con- siderably 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 usually 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.

Experiment 3. — A similar experiment to the last, with exactly the same results. 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. Experiment 5. — Leaf immersed at 130° (54°'4 Cent.), and the water raised to 145° (62° '7 Cent.), there was no immediate in- flection ; 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.