Insectivorous Plants

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 * Sachs states (' Traite de Bo- after they were exposed for 1 m. 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 proto- plasm being extremely small; in other cells, especially in the exterior tentacles, there was much greenish-brown pulpy matter.

Experiment 8. — A leaf was plunged and waved about for a few minutes in water at 140° (6CP 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 tempe- rature as 140°, and in only one leaf out of four, after a similar immersion at a temperature of 115° Fahr. On the other hand, with two leaves, one placed in water at 145° (6:2° '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.

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 back- wards. 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.

Ejperiment 10. — A leaf was plunged in water at 150° to 150i° (65° • 5 Cent.) ; it became somewhat flaccid, with the outer ten- tacles 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.

Experiment 11. — A leaf was immersed in water at 145° (G20<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 proto- plasm, after having been exposed to a high temperature for a few minutes, is capable of aggregation when afterwards sub- jected to the action of carbonate of ammonia, unless the heat has been sufficient to cause coagulation.

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 tem- perature of 130° (540-4 Cent.) never causes the imme- diate inflection of the tentacles, though a temperature from 120° to 125° (4S°'S to 51°-6 Cent.) quickly pro- duces 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 car- bonate of ammonia, they become inflected and their protoplasm undergoes aggregation. This great dif- ference in the effects of a higher and lower tempera- ture may be compared with that from immersion in strong and weak solutions of the salts of ammonia ; foi the former do not excite movement, whereas the lattei act energetically. A temporary suspension of the

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 car bouate so strong that it would paralyse ordinary leaves and cause no inflection.

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 ammo- nia, they generally, though not always, become in- flected ; and the protoplasm within their cells under- goes 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. Ex- posure for a few minutes to a temperature of 145° sometimes causes some few of the more sensitive glands to be speckled with the porcelain-like appear- ance ; and on one occasion this occurred at a tempera- ture of 140° (60° Cent.). On another occasion, when a leaf was placed in water at this temperature of only 140°, and left therein till the water cooled, every gland became like porcelain. Exposure for a few minutes to a temperature of 150° (65°'5 Gent.) gene- rally produces this effect, yet many glands retain a

pinkish colour, and many present a speckled appear- ance. This high temperature never causes true inflec- tion ; 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 tem- perature of 150° Fahr., the protoplasm, if subsequently subjected to carbonate of ammonia, instead of under- going 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° (680>8 Cent.), escaped being rendered porcellanous ; * and the protoplasm in the cells close beneath these glands underwent some slight, though imperfect, degree of aggregation.

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°.f * As the opacity and porcelain- differences in the results above probably due to the coagulation t It appears that cold-blooded of the albumen, I may add, on the animals are, as might have been authority of Dr. Burdon Sander- expected, far more sensitive to an son, that albumen coagulates at increase of temperature than is about 155°, but, in presence of Drosera. Thus, as I hear from Dr. acids, the temperature of coagula- Burdon Sanderson, a frog begins tion is lower. The leaves of Dro- to be distressed in water at a tern- sera contain an acid, and perhaps perature of only 85° Fahr. At 95° a difference in the amount con- the muscles become rigid, and the taincd may account for the slight animal dies in a stiffened couditiou

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. PUB EFFECTS OF NON-NITROGENOUS AND NITROGENOUS ORGANIC FLUIDS

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. WHEN, in 1860, 1 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 nitro- genous matter ; and the results are worth giving.

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, oivln 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 col- lected 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

is kept in a room, and some of the central and sub- marginal 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 move- ment 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 ad- hesive fluid and the consequent drawing together of the tentacles.

First for the non-nitrogenous fluids. As a pre- liminary 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 in- flected ; but this Qiay 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.

Gum arable. — 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 ou the discs from 24 hrs. to 44 hrs. ; generally about 30 lirs. 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.

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 lirs. ; btit no effect was produced. 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 com- merce generally contains a trace of gluten, and this nitrogenous substance causes inflection, as we shall see in the next chapter.

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 ascer- tain 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 inflec- tion 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.

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 ten- tacles inflected. It will, however, be shown in a future place, that cut-off leaves immersed in olive oil are powerfully affected.

Jnfusion and Decoction of Tm. — 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 after- wards 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.

We thus see that, excluding the experiments with water, sixty-one leaves were tried with drops of the above-named non-nitrogenous fluids ; and the tentacles were not in a single case inflected. 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.

J//7A-. — 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 occa- sion the blade of a leaf was much inflected in 5 hrs. after a drop of milk had been placed on it.

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 ten- tacles 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.

Albumen (fresh from a hen's egg), placed on seven leaves, caused the tentacles of six of them to be Avell 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 taused the tentacles to bend inwards in 12 hrs. Cold Filtered Infusion of Haw 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

on with other substances, and it was found to act most ener- getically, but as no exact account of these trials was kept, they are not here introduced. 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. 80 m., and greatly so in 20 hrs. The action of this fluid no doubt is due either to the saliva or to some albu- minous matter* mingled with it, and not, as we shall see in the next chapter, to rnucin or the chemical principle of mucus.

Saliva. — Human saliva, when evaporated, yieldsf 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 con- tains must be small. Nevertheless, drops placed on the discs of eight leaves acted on them all. In one case all the exterior ten- tacles, 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 condi- tion ; 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.

Ixinylass. — Drops of a solution about as thick as milk, and of a still thicker solution, were placed on eight leaves, and the ten- tacles 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.

* Mucus from the air-passages to contain some albumen, is said in Marshall, 'Outlines of t M tiller's 'Elements of Physio Physiology,' vol. ii. 1867, p. 3C4, logy,' Eng. Trans, vol. i. p. 5H. 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 ; tho 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 -^ 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 F|^ 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 ten- tacles strongly inflected.

Altogether I experimented on sixty-four leaves with the above nitrogenous fluids, the five leaves tried only with the extremely weak solution of isin- glass 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-nitro- genous 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

nitrogenous matter by the glands of the tentacles on the disc. Some of the leaves which were not affected by the non-nitrogenous fluids were, as above stated, imme- diately afterwards tested with bits of meat, and wer« 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 move- ment 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.