seeds are often blown on to the viscid leaves of plants growing in a
state of nature; but this can hardly fail sometimes to occur, as we
shall hereafter see in the case of Pinguicula. If so, Drosera will
profit to a slight degree by absorbing matter from such seeds.]
A Summary and Concluding Remarks on the Digestive Power of Drosera.
When the glands on the disc are excited either by the absorption of
nitrogenous matter or by mechanical irritation, their secretion
increases in quantity and becomes acid. They likewise transmit [page
129] some influence to the glands of the exterior tentacles, causing
them to secrete more copiously; and their secretion likewise becomes
acid. With animals, according to Schiff,* mechanical irritation excites
the glands of the stomach to secrete an acid, but not pepsin. Now, I
have every reason to believe (though the fact is not fully
established), that although the glands of Drosera are continually
secreting viscid fluid to replace that lost by evaporation, yet they do
not secrete the ferment proper for digestion when mechanically
irritated, but only after absorbing certain matter, probably of a
nitrogenous nature. I infer that this is the case, as the secretion
from a large number of leaves which had been irritated by particles of
glass placed on their discs did not digest albumen; and more especially
from the analogy of Dionaea and Nepenthes. In like manner, the glands
of the stomach of animals secrete pepsin, as Schiff asserts, only after
they have absorbed certain soluble substances, which he designates as
peptogenes. There is, therefore, a remarkable parallelism between the
glands of Drosera and those of the stomach in the secretion of their
proper acid and ferment.
The secretion, as we have seen, completely dissolves albumen, muscle,
fibrin, areolar tissue, cartilage, the fibrous basis of bone, gelatine,
chondrin, casein in the state in which it exists in milk, and gluten
which has been subjected to weak hydrochloric acid. Syntonin and
legumin excite the leaves so powerfully and quickly that there can
hardly be a doubt that both would be dissolved by the secretion. The
secretion
* Phys. de la Digestion, 1867, tom. ii. pp. 188, 245. [page 130]
113