Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/152

 140 of Asclepiadacex, and Martynia, one of the Pedalinex, have also been described as insectivorous, as well as Caltha dionsefolia and several Aroids. Even Anomoclada, a South American liverwort, and a fern (Elaphoglossum glutinosum) have been described by Spruce as capturing numerous insects. All these cases, however, require much further investigation. The connate leaves of Dipsacus frequently enclose water in which insects are drowned, and Francis Darwin has discovered protoplasmic filaments which are emitted by the cells of certain glands within these cups, and which appear to absorb the products of decomposition. A similar process has recently also been shown by Ludwig to occur in Silphium, an allied genus. Conclusion. When Mr Darwin s work appeared, nume rous objections were made to accepting his conclusions, on the a priori ground that digestion was too purely an animal function to be conceivable of plants. Morren demolished these by showing that digestion the conversion of insoluble and indiffusible proteids, fats, and amyloids into soluble and diffusible compounds by means of appropriate ferments is not confined either to animals or to carnivorous plants, but is a universal property of living beings, in fact the necessary preliminary of all assimilation. Not only are all the important animal digestive ferments represented among plants, but vegetable physiologists have made us acquainted with several ferments synaptase, erythrozyme, myrosine, &amp;lt;fec. which have no known analogues in the animal kingdom. It is merely the exudation, not the existence, of the ferment, then, which is remarkable in carnivorous plants, and this Darwin suggests might begin by an exosmose accompanying the absorption of animal matter by any plant possessing viscid glandular hairs, and, once set up, would be perfected by natural selection. Insectivorous plants too are not the only ones which exhibit peculiarities of nutrition. The true parasites absorb the juices of the plants which they infest, and, not to mention the fungi, many of which subsist partly or wholly on animal matter, the phanerogamous saprophytes (Neottia, Monotropa, &c.) live by absorbing the partially decomposed materials of other plants ; and from the absorption of vegetable to that of animal matter the transition is easy. The reciprocal case too occurs in the animal kingdom ; animals possessing chlorophyll have been shown to nourish themselves like plants, without feeding, by decomposition of carbonic acid and the formation of starch in sunlight, and thus carnivorous plants trespassers into the animal kingdom are paralleled by vegetating animals. Thus, then, we have only to change our standpoint, and look, not at the anomalous plant or animal, but at the essentially similar cells, and the yet more essentially similar protoplasm of which both are composed, to see that their apparent anomalies are but additional proofs of the unity of nature. But a more serious criticism affected the completeness of Darwin s work. Though Knight in 1818 had thought plants of Dionxa on which he placed morsels of beef grew more luxuriantly than others not so treated, many observers have since failed to see any improvement on insectivorous plants when regularly fed, or any disadvantage when pre vented from obtaining animal food altogether ; while others have even asserted that animal food was hurtful, having injured or killed their plants by feeding. In the latter case the explanation was of course that the feeding was excessive, but to meet the objections of the former a very careful research was undertaken by Francis Darwin. He took six plates full of thriving plants of sundew, and divided off each by a transverse bar. Then, choosing the least flourishing side of each, he placed, on June 12, 1877, roast meat, in morsels of about -^ of a grain on the leaves, and renewed the dose occasionally. The plants on the fed sides were soon clearly greener than those on the starved sides, and their leaves contained more chlorophyll and starch, In less than two months the number of flowerstalks was half as numerous again on the fed as on the unfed sides, while the number and diameter of the leaves and the colour of the flowerstalks all showed a great superiority. The flowerstalks were all cut at the end of August, when their numbers were as 165 to 100, their total weight as 230 to ,100, and the average weight per stem as 140 to 100 for the fed and unfed sides respectively. The total numbers of seed capsules were as 194 to 100, or nearly double, and the average number of seeds in each capsule as 12 to 10 respectively. The superiority of the fed plants over the unfed was even more clearly shown by comparing their seeds, the average weights per seed being as 157 to 100, their total calculated number as 240 to 100, and their total weight as 380 to 100. The fed plants, though at the commencement of the experiment in a slight minority, at the end of the season exceeded the unfed by more than 20 per cent., while the following spring the young plants which sprang up on the fed side exceeded those on the other by 18 per cent, in number and by 150 per cent, in total weight, so that, in spite of the relatively enormous quantity of flowerstalk produced by the fed plants during the previous summer, they had still been able to lay up a far greater store of reserve material. It is to be remarked that the beneficial effect of feeding, although distinct in the vegetative system, is much more remarkable in the reproductive, a fact which explains the unfavourable opinion of previous observers. These results were also independently arrived at by three German observers, Rees, Kellerman, and Von Eiiumer, who used aphides instead of roast meat. The question of the utility of the carnivorous habit may thus be considered as no less indisputable than its existence. Bibliography. Besides Darwin, Insectivorous Plants, 1875, and Hooker, Brit. Assoc. Report, 1874, p. 102, the reader may with advantage consult the following authorities. From them he can easily obtain complete references to the minor papers, which are too numerous for mention here. General Subject : Planch on, &quot;Les Plantcs Carnivores,&quot; Rev. d. Deux Monties, February, 1876; Dodel- Fortjlttustrirtcs PJlanzcnleben, Zurich, 1880 ; Morren, La Theoric cles Plantcs Carnivores et Irritablcs, 2d cd., Liege, 1876 ; Cramer, Ucb. d. InscJctfressenden Pflanzen, Zurich, 1877 ; Driide, in Encyc, d. Natunoissenschaften, &quot; Bot.,&quot; bd. i., 1879; Magnin, Bull. Soc. d. Etudes Sci. de Lyon, No. 2, 1877. Droscra: Trecul, &quot; Organ d. Glandes Fed. des Feuilles d. D. rot.,&quot; Ann. Sc. Nat. Bot., 1855; Nitschke, &quot;Anat. d. Sonnenthaublattcs,&quot; Bot. Zeit., 1861, and other papers in Bot. Zcit., 1860-61 ; Morren, &quot;Note sur le Droscra binata,&quot; Bull, de I Acad. Roy. de Belgique, 1875. Dionxa: San derson, Proc. Roy. Soc. Lond., No. 147, 1873, and Nature, x., 1874 ; C. de Candolle, &quot; Sur la Struct, et les Mouvements des Feuilles du D. inusdpula,&quot; Archives des Sci. de Geneve, April 1876 ; Kurtz, &quot;Anat. d. Blattes d. D. muscipula,&quot; Archiv f. Anat. . Physiol., 1876; Munlc, &quot;Dieelekt. u. Bewegungserschein,&quot; &c., Archiv f. Anat. u. Physiol., 1876; Fraustadt, &quot;Anat. d. Veget. Organe v. D. muscipula,&quot; Com s Bcitr. a. Biol. d. Pfl., 1876 ; T. A. G. Balfour, &quot;Exp. on D. mutcipula,&quot; Trans. Bot. Soc. Edin., 1874-5, and Nov. 1878. Aldrovanda, Utricularia, PinguicuJa : Duval-Jonve, &quot; Notes s. q. plantes dites inscctivorcs,&quot; Bull. Soc. Bot. Fr., Ixxiii., 1876 ; Benisch, &quot;Ueb. V. mtlgaris,&quot; Dcnlcschr. d.k. lot. Gescllsch., bd. iv., 1859; Cohn, &quot;Ueb. d. Function d. Blasen v. Aldrovanda u. Utricularia,&quot; Bcitr. z. Biol. d. Pfl., bd. i. ; Morren, &quot; Observ. s. 1. precedes insecticides du Pinguicula,&quot; Bull. Acad. Roy. dc Bclcj., 1875; Klein, ^Pinguicula Alpina,&quot; Bcitr. z. Biol. d. Pfl., bd. iii., lift. 2. Sarraccnia, Darlinglonia, Ccplialotus, &c. : Law- son Tait, &quot;On Structure of Pitcher Plants,&quot; Midland Naturalist, 1879; Dickson, &quot;On the Morphology of the Pitcher of Cepkalotus,&quot; Journ. of Bot., May 1881 ; Spruce, &quot;On Anomoclada,&quot; Journ. of Bot., 1876; Heckel, Bull. Bot. Soc. Fr., 1876. Digestion and Absorption: Rees u. Will, &quot;Einige Bemerk. ii. fleischfr. Pflanz en,&quot; Bot. Zcit., 1875 ; Bennett, &quot;On Absorptive Glands of Car nivorous Plants,&quot; Monthly Micro. Journ., 1876 ; Clark, &quot;On Ab sorption by Leaves of Carniv. PI.,&quot; Journ. of But., 1875 ; Lawson Tait, &quot;On the Digestive Princ. of Plants, &quot; Phil. Soc. Birminyh., 1878 ; Morren, &quot;La Digestion Vegetale,&quot; JSztZZ. Acad. Roy. deBclg., 1875 ; Geddes, &quot;On the Physiol. and Histol. of Convoluta,&quot; Proc. Roy. Soc. Lond., 1879 ; F. Darwin, &quot;Exp. on Nutrition of Dro scra,&quot; Journ. Linn. Soc, Bot., 1878. (P. GE.)