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Page:Popular Science Monthly Volume 65.djvu/434

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THE POPULAR SCIENCE MONTHLY.

sun-dew had their origin in the course of the evolution of the plant world? Such a question will ever remain a mystery, and on its solution we shall be able merely to throw an occasional ray of light. Very many plants have their stems or flower-stalks beset with glandular hairs secreting sticky substances; an example in point, the clammy cuphea of our fields which sticks to the fingers tenaciously if we attempt to pluck its flowers. So far as known, the sticky secretions serve the plant in no way other than making it unpleasant browsing for herbivorous animals and ridding it of marauding ants, which become stuck to the glands and seldom escape. Might not such a condition have existed in the ancestors of the sun-dew? Might not the accidental catching of insects in this manner have formed the starting-point for the habit which is now so essential to the plant? Pitchered leaves are found too in many plants, and in many of them catch insects by pure accident, for example, the Dischidia of the East Indies. It is quite possible that further study of such cases may reveal new examples of the insectivorous habit, or may discover plants which have an imperfect or partial dependence on insect food, and any such discoveries would throw light on the development of the habit in its full-fledged possessors.

Marvelous as are the adaptations of the insectivorous plants, they have not been all these years upon the earth without certain crafty insects having learned not only to escape falling a prey to them, but to use them to their own ends. The pitchers of the Californian pitcher-plant are the home of a small moth which is provided with sharp spurs on its middle legs, which enable it to crawl easily over the slippery surfaces of the interior. So fearless has the moth become that it even lays its eggs in the interior of the pitcher, and here, protected from all the manifold dangers of the outside world, they hatch out in security. The young caterpillars spin a web over the slippery surfaces and the projecting hairs, making a safe path for themselves to the outside. There is a blow-fly which is able, too, to crawl over the slippery surfaces by aid of peculiar claws which give it a good sure footing. The grubs of this fly hatch out in the water of the pitcher and, far from yielding themselves up as food, they live here their brief term of larval life, and escape by boring a hole in the side of the pitcher.

In the South African hills grows a sort of bushy sun-dew, known locally as the 'fly-bush' (Roridula). This plant is a large consumer of insect food, owing to its size and the completeness with which twigs and leaves and even parts of the flower are covered with glandular hairs. Among its branches a spider has been found to spin its web. Not content with the supply of flies from its web. however, the spider goes forth upon the twigs of the fly-bush, and walking about in safety