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Here we have the faculty of movement to a definite end, upon external irritation, of the same nature with that displayed by Dionaea and Drosera, although slower for the most part than even in the latter. But the movement of the hour-hand of the clock is not different in nature or cause from that of the second-hand.
In the Dionaea Muscipula there is a still more wonderful contrivance to prevent the depredations of insects: The leaves are armed with long teeth, like the antennæ of insects, and lie spread upon the ground round the stem; and are so irritable, that when an insect creeps upon them, they fold up, and crush or pierce it to death.
The evidence from experiment, shortly summed up, is, that insects alive or dead, and also other nitrogenous bodies, excite these glands to increased secretion; the secretion then becomes acid, and acquires the power of dissolving solid animal substances that is, the power of digestion in the manner of Drosera and Dionaea.
But the direct evidence of this is furnished only by the related carnivorous plant, Dionaea, from which the secretions, poured out when digestion is about to begin, may be collected in quantity sufficient for chemical examination.
Observations on the Irritation of Vegetables, by T. E. Smith, M. D. Addition to the note on Silene. I saw a plant of the Dionaea Muscipula, Flytrap of Venus, this day, in the collection of Mr.
As there are various plants upon whose glandular hairs or glutinous surfaces small insects are habitually caught and perish, it might be pure coincidence that the most effectual arrangement of the kind happens to occur in the nearest relatives of Dionaea.
We do not hesitate to class amongst vegetables the Drosera, the Dionaea, the Pinguicula, which are insectivorous plants. On the other hand, the fungi, which occupy so considerable a place in the vegetable world, feed like animals: whether they are ferments, saprophytes or parasites, it is to already formed organic substances that they owe their nourishment.
A small fly is held so fast, and in its struggles comes in contact with so many of these glutinous globules, that it seldom escapes. The result is much the same to the insect, whether captured in the trap of Dionaea or stuck fast to the limed bristles of Drosera.
As to the Drosera, the Dionaea, and insectivorous plants in general, they are fed by their roots, like other plants; they too fix, by their green parts, the carbon of the carbonic acid in the atmosphere. Their faculty of capturing, absorbing and digesting insects must have arisen late, in quite exceptional cases where the soil was too poor to furnish sufficient nourishment.
Darwin, with the same results, and with a small but highly-curious additional one namely, that the fluid secreted in the trap of Dionaea, like the gastric juice, has an acid reaction. By a prick with a sharp lancet at a certain point, he has been able to paralyze one-half of the leaf-trap, so that it remained motionless under the stimulus to which the other half responded.
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