CARNIVOROUS PLANTS. 
357 
be possible — and indeed this has been maintained by some — that 
these arrangements were merely a contrivance for facilitating 
the decay of the living insects or other entrapped organic sub- 
stances ; and that the nutrient matter . resulting from their 
decay, being carried to the ground, fed the plants through the 
ordinary medium of the rootlets. To Darwin must be assigned 
the merit of having for the first time clearly and unmistakably 
demonstated a true process of digestion carried on by the foliar 
organs of plants ; although Dr. Hooker and others had earlier 
given good reason for a belief in its existence in the case of 
Nepenthes and other pitcher plants. The viscid secretion from 
the glands of Drosera is, in the normal condition, nearly or 
quite neutral to test-paper. But as soon as it is excited by 
contact with any inorganic or organic substance, it becomes 
distinctly acid, and more strongly so after the tentacles have 
remained for some time closely clasped over any object. A 
small quantity of the substance thus obtained was sent for 
analysis to Professor Frankland, who found no trace of 
hydrochloric, sulphuric, tartaric, oxalic, or formic acid ; but, as 
far as could be determined from the very minute quantity sub- 
mitted to analysis, distinct indications of an acid belonging to 
the acetic or fatty series, probably propionic, with a possible 
admixture of acetic and butyric. A still more interesting result 
of Mr. Darwin’s experiments was the conclusion that in 
addition to the acid a substance analogous to pepsin, and acting 
as a ferment, is secreted by the glands, but only when excited 
by the presence of digestible, i.e. nitrogenous, matter. This 
singular result, affording so striking an analogy to the phe- 
nomena of digestion by the stomach of an animal, is in 
harmony with the observation of Dr. Hooker in the case of 
Nepenthes , that the fluid formed in the pitchers of that plant 
entirely loses its power of digestion when removed from the 
pitcher and placed in a glass vessel, although it is even then dis- 
tinctly acid. The following substances were found to be com- 
pletely dissolved in the secretion, viz., albumen, muscle, fibrin, 
areolar tissue, cartilage, the fibrous basis of bone, gelatin, 
chondrin, casein in the state in which it exists in milk, and 
gluten which has been subjected to the action of weak hydro- 
chloric acid ; while epidermic productions, fibro-elastic tissue, 
mucin, pepsin, urea, chitine, cellulose, gun-cotton, chlorophyll, 
starch, fat, and oil, are not acted on either by the secretion of 
Drosera, nor, as far as is known, by the gastric juice of animals. 
The power possessed by Drosera of obtaining nourishment 
through the leaves receives confirmation from a valuable series 
of experiments by Dr. Lawson Tait,* who announced, inde- 
See “Nature,” for July 29, 1875. 
