Insectivorous Plants eBook

This eBook from the Gutenberg Project consists of approximately 462 pages of information about Insectivorous Plants.

Besides the glands which are borne on longer or shorter pedicels, there are numerous ones, both on the upper and lower surfaces of the leaves, so small as to be scarcely visible to the naked eye.  They are colourless and almost sessile, either circular or oval in outline; the latter occurring chiefly on the backs of the leaves (fig. 14).  Internally they have exactly the same structure as the larger glands which are supported on pedicels; [page 334] and indeed the two sets almost graduate into one another.  But the sessile glands differ in one important respect, for they never secrete spontaneously, as far as I have seen, though I have examined them under a high power on a hot day, whilst the glands on pedicels were secreting copiously.  Nevertheless, if little bits of damp albumen or fibrin are placed on these sessile glands, they begin after a time to secrete, in the same manner as do the glands of Dionaea when similarly treated.  When they were merely rubbed with a bit of raw meat, I believe that they likewise secreted.  Both the sessile glands and the taller ones on pedicels have the power of rapidly absorbing nitrogenous matter.

The secretion from the taller glands differs in a remarkable manner from that of Drosera, in being acid before the glands have been in any way excited; and judging from the changed colour of litmus paper, more strongly acid than that of Drosera.  This fact was observed repeatedly; on one occasion I chose a young leaf, which was not secreting freely, and had never caught an insect, yet the secretion on all the glands coloured litmus paper of a bright red.  From the quickness with which the glands are able to obtain animal matter from such substances as well-washed fibrin and cartilage, I suspect that a small quantity of the proper ferment must be present in the secretion before the glands are excited, so that a little animal matter is quickly dissolved.

Owing to the nature of the secretion or to the shape of the glands, the drops are removed from them with singular facility.  It is even somewhat difficult, by the aid of a finely pointed polished needle, slightly damped with water, to place a minute particle of any kind on one of the drops; for on withdrawing the [page 335] needle, the drop is generally withdrawn; whereas with Drosera there is no such difficulty, though the drops are occasionally withdrawn.  From this peculiarity, when a small insect alights on a leaf of Drosophyllum, the drops adhere to its wings, feet, or body, and are drawn from the gland; the insect then crawls onward and other drops adhere to it; so that at last, bathed by the viscid secretion, it sinks down and dies, resting on the small sessile glands with which the surface of the leaf is thickly covered.  In the case of Drosera, an insect sticking to one or more of the exterior glands is carried by their movement to the centre of the leaf; with Drosophyllum, this is effected by the crawling of the insect, as from its wings being clogged by the secretion it cannot fly away.

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Insectivorous Plants from Project Gutenberg. Public domain.
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