Page:Popular Science Monthly Volume 65.djvu/421

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417
SOME PLANTS WHICH ENTRAP INSECTS.

SOME PLANTS WHICH ENTRAP INSECTS.
By FORREST SHREVE,

THE JOHNS HOPKINS UNIVERSITY.

WE seldom give a thought to the fact that plants need food. They had such unite, motionless lives that it is difficult to believe that they have, like ourselves, a bread-and-butter problem staring them constantly in the face. We watch the geraniums and begonias of our window-garden grow and bloom with nothing to nourish them but a few handfuls of earth and a little water. Surely their food problem must be a simple one if the substances necessary to the formation of stem and leaves and blossom can all be got from so little earth. Wherein lies all the difficulty about poor soil which besets the farmer, and why must he buy tons of plant food and drill it carefully into the ground in order to get a remunerative crop of grain? The whole trouble for the farmer arises from the scarcity in the soil of two or three food elements which, although highly important, form I tut a small part of the total weight of growing plants. The foremost of these scarcer foods, nitrogen, has been a source of difficulty not only to man, but to a large number of plants as well, which have been forced to adopt a means of getting it which is radically different from all other methods of plant nutrition, so much so indeed that it was long looked upon as a mere meaningless 'freak of nature.' This method is the catching of insects.

Every one has heard of the pitcher-plant or perhaps seen its urnlike leaves half filled with water. Innocent looking as are these leaf-pitchers, and casual as may seem the presence of three or four drowned flies in the water which they contain, yet in truth each pitcher is a veritable trap, clever in design and effective in its purpose of alluring and drowning insects. Different in look, but to the same purpose, are the leaves of the sun-dew. Its bristling hairs bear beads of jelly, not for the mere splendor of their dazzling brilliance, but to allure, catch and hold fast gnats and mosquitoes, all to the same end as in the pitcher-plant,—supplying a shortage of nitrogen in the food. Not these two plants alone, but a large group of nearly four hundred species, are insect trappers, carnivorous or, as they are more commonly called, insectivorous plants. The varied devices which these plants possess for alluring insect prey, catching, holding and utilizing it furnish matter for one of the most interesting chapters in all botanical science.