Insectivorous Plants

The utricles contained much dbris or dirty matter, which seemed organic, though no distinct organisms 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.

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 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.

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.

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.

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 antennae 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 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?

CONCLUSION. – 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.

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 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.

notes

1

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, [] 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.

2

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."

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.

3

Nitschke has elaborately described and figured these papillae, 'Bot. Zeitung,' 1861, pp. 234, 253, 254.

4

'Bot. Zeitung,' 1860, p. 246.

5

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 [] 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.)

6

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.

7

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."

8

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.

9

With respect to plants, Sachs, 'Trait de Bot.' 3rd edit., 1874, p. 864. On blood corpuscles, see 'Quarterly Journal of Microscopical Science,' April 1874, p. 185.'

10

According to Hofmeister (as quoted by Sachs, 'Trait 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.

11

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 ('Trait de Botanique,' 1874, pp. 772, 854) that the most different kinds of plants all perish if kept for 10 m. in water at 45o to 46 °Cent., or 113o to 115o Fahr.; and he concludes that the protoplasm within their cells always coagulates, if in a damp condition, at a temperature of between 50oand 60 °Cent., or 122o to 140o Fahr. Max Schultze and Khne (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 [] altered by a very brief exposure to a temperature of 118 1/2o 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 168o Fahr.; Humboldt, at 185o Fahr.; and Descloizeaux, at 208o Fahr.)

12

Sachs states ('Trait 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 47o to 48 °Cent., or 117o to 119o Fahr.

13

'Trait de Bot.' 1874, p. 1034.

14

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.

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 85o Fahr. At 95o the muscles become rigid, and the animal dies in a stiffened condition.

15

Mucus from the air-passages is said in Marshall, 'Outlines of Physiology,' vol. ii. 1867, p. 364, to contain some albumen.

Mller's 'Elements of Physiology,' Eng. Trans. vol. i., p. 514.

16

Watts' 'Dictionary of Chemistry,' vol. iii., p. 568.

'Leons sur la Phys. de la Digestion,' tom. i, p. 379; tom. ii. pp. 154, 166, on legumin.

17

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.

18

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.

19

In all my numerous experiments on the digestion of cubes of albumen, the angles and edges were invariably first rounded. Now, Schiff states ('Leons 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."