Insectivorous Plants

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."

20

Sachs remarks ('Trait 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.

21

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.

22

'Leons phys. de la Digestion,' 1867, tom. ii. pp. 114-126.

23

'Leons phys. de la Digestion,' tom. ii. p. 145.

24

Dr. Lauder Brunton, 'Handbook for the Phys. Laboratory,' 1873, pp. 477, 487; Schiff, 'Leons phys. de la Digestion,' 1867, p. 249.

25

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.

26

'Leons,' &c. tom. ii. page 151.

27

Dr. Lauder Brunton, 'Handbook for Phys. Lab.' p. 529.

28

'Leons' &c. tom. ii. page 153.

29

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.

Watts' 'Dict. of Chemistry,' vol. ii. 1872, p. 873.

30

Watts' 'Dictionary of Chemistry,' vol. ii. page 874.

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.

31

See, for instance, Schiff, 'Phys. de la Digestion,' 1867, tom. ii., p. 38.

32

'Leons phys. de la Digestion,' 1867, tom. ii., p. 304.

33

'Phys. de la Digestion,' 1867, tom. ii. pp. 188, 245.

34

See the classification adopted by Dr. Michael Foster in Watts' 'Dictionary of Chemistry,' Supplement 1872, page 969.

35

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.

36

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.

37

Miller's 'Elements of Chemistry,' part ii. p. 107, 3rd edit. 1864.

38

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.)

39

Miller's 'Elements of Chemistry,' 3rd edit. pp. 337, 448. inflection. After describing the experiments, a few concluding remarks will be added.

40

See articles on Glycerine and Oleic Acid in Watts' 'Dict. of Chemistry.'

41

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;

42

Miller's 'Elements of Chemistry,' part i. 1867, p. 87.

43

'Quarterly Journal of Microscopical Science,' April 1874, p. 185.

44

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.

45

Dr. Fayrer, 'The Thanatophidia of India,' 1872, p. 150.

46

'Proceedings of Royal Society,' Feb. 18, 1875.

47

'Gardener's Chronicle,' 1874, p. 671. Nearly similar observations were made in 1798 by B. S. Barton.

48

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.

49

Dr. Fayrer, 'The Thanatophidia of India,' 1872, p. 4.

50

Sachs, 'Trait de Bot.' 1874, pp. 846, 1037.

51

'Bot. Zeitung,' 1860, p. 234.

52

'Bot. Zeitung.' 1860, p. 437.

53

'Bot. Zeitung,' 1860, p. 240.

54

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.

55

'Videnskabelige Meddelelser de la Soc. d'Hist. nat. de Copenhague,' Nos. 10-12, 1872, woodcuts iv. and v.

56

Sachs, 'Trait de Bot.' 3rd edit. 1874, p. 1038. This view was, I believe, first suggested by Lamarck. Sachs, ibid. p. 919.

57

'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.

58

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.

59

'American Naturalist,' December 1873, page 705.

60

'Gardener's Chronicle,' 1874, p. 209.

61

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.

'Gardener's Chronicle,' 1874, p. 464.

62

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."

63

According to Dr. Curtis, in 'Boston Journal of Nat. Hist,' vol. i 1837, p. 123.

64

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.

65

Proc. Royal Soc.' vol. xxi. p. 495; and lecture at the Royal Institution, June 5, 1874, given in 'Nature,' 1874, pp. 105 and 127.

66

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.

I am greatly indebted to this distinguished naturalist for having sent me a copy of his memoir on Aldrovanda, before its publication in his 'Beitrge zur Biologie der Pflanzen,' drittes Heft, 1875, page 71.

67

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.

68

Sachs, 'Trait de Bot.,' 3rd edit. 1874, p. 1026.

69

The distinction between true absorption and mere permeation, or imbibition, is by no means clearly understood: see Mller's 'Physiology,' Eng. translat. 1838, vol. i. p. 280.

70

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.

71

'Comptes rendus,' June 15, 1874. A good abstract of this paper is given in the 'Gardener's Chronicle,' July 11, 1874.

72

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.