Insectivorous

Collier's New Encyclopedia (1921)

CARNIVORor OUS PLANTS, plants which deviate from the usual plant method of obtaining nutriment from the soil and the air, and feed or subsist on insects or other small animals, which they capture by ingenious contrivances. In these respects they make an approach to the animal class of nutriment and modes of food getting, setting traps, as it were, to catch their prey. These traps consist in the leaf, which is modified in some peculiar way to adapt it to the purpose. Among the insect-catching plants, one of the most notable is the Venus fly-trap (Dionæa muscipula) of the Carolinas, the separated halves of whose leaves close instantly when their surfaces, which bear irritable hairs, are touched. The edges bear 12 to 20 long teeth, which closely interlock, the whole forming a live insect trap. The fly or other insect which has caused the closure is held till its soft parts are digested and its juices are absorbed by the leaf, when the latter opens again. A digestive secretion is thrown out, and the closed leaf acts as a true stomach, the work of digestion going on for a week or two. The sundews (genus Drosera, of which there are about 100 species) are notable for their power of capture. In these the leaves are thickly studded with hair or tentacles, which secrete a clear liquid, which is extremely viscid, holding any insect which touches it. Of a different character are the pitcherplants, of which there are many kinds in various parts of the world. In these the leaf takes the form of a vase, cup, or tube, with a hood or cover at the top by which the entrance may be closed. Water gathers within these hollow leaves, and, in some cases at least, a liquid secretion from the plant. In some species sweet drops are found on the outside of the leaf leading upward to the mouth, within which other honeyed drops appear. These are arranged in a trail to lure the unsuspecting insect to enter the dangerous cage. On the hood and within the pitcher are stiff hairs or bristles pointing downward, and acting to prevent the prey from crawling out again. The California pitcher-plant has a bright-colored appendage hanging from the opening as a lure to the insect. In some cases the whole leaf is converted into a pitcher. In East India pitcherplants, Nepenthes, of which there are 31 species, are of this character. In these small cups flies and other insects are caught in large numbers. Some plants form their traps by uniting the bases of opposite leaves. Such is th the case with Silphium perfoliatum, the cup-plant of the Western prairies. The teasel has a similar structure. The bladderworts (Utricularia), of which there are about 160 species, are aquatic plants which bear curious little sacs, or bladders, on their dissected leaves, which float in the water. These have open mouths which are lined with bristles, and which, while offering ready entrance to_minute insects, prevent their return. When grown in the greenhouse these plants are found to flourish without insect food.