Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] Leaf of sundew closing over captured insect. trap. Each margin cf the leaf is provided with a row of hairs; there are also three central hairs on each side of the midrib. The hairs are sensitive to a stimulus from without. The blade is so constructed that the slightest stimulus causes a closing of the leaf along the midrib. The surface of the leaf is provided with many tiny glands, which pour out a fluid capable of digesting proteid
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] Leaf of sundew closing over captured insect. trap. Each margin cf the leaf is provided with a row of hairs; there are also three central hairs on each side of the midrib. The hairs are sensitive to a stimulus from without. The blade is so constructed that the slightest stimulus causes a closing of the leaf along the midrib. The surface of the leaf is provided with many tiny glands, which pour out a fluid capable of digesting proteid food. Thus an in- sect, caught between the halves of che leaf blade, is held there and slowly digested. Sundew. — In the sundew the leaves are covered with long glandular hairs, each of which is extremely sensitive to the stimulus of any nitrogenous substance. These hairs exude a clear, sticky fluid which first ren- ders more difficult the escape of the insect caught in the hairs, and then digests the nitrogenous parts of the insect thus caught. Charles Darwin, in a series of experi- ments, found that these hairs do not respond to the stimu- lus of falling raindrops, but that a bit of hair weighing only y 8 y JO- of a grain is enough to cause the slight bending of the hairs. Pitcher Plants. — The common pitcher plant has an urn-shaped leaf which is modi- fied to hold water. Many small flies and other insects find their way into the pitcher and are eventually drowned in the cup. Whether the plant actually makes use of the food thus obtained is a matter un- settled. In a tropical form, called Nepenthes, the petiole of the leaf forms the pitcher, the blade of the leaf forming a kmd of lid. In the fuU- grcwn plants this lid stands Pitcher plant; a, leaf; 6, cross section; c, longitudinal open, perhaps as an attrac- section. Note the insects at the bottom, and the -• j. • x tt i ^ inward-pointing hairs at the top. tion to msects. Honey glands
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