Page:An introduction to physiological and systematical botany (1st edition).djvu/238

 208 appear about the veins on their under sides, and the cuticle scales off. Succulent leaves, though so thick and firm as many of them are, have been observed to be peculiarly sensible to light, while other plants, as Mallows, according to Bonnet, are much less so. The Miseltoe, Viscum album, ''Engl. Bot. t.'' 1470, the two sides of whose leaves are alike in appearance, and both equally, in general, presented to the light, are not found to turn upon any change in the posture of the branch. Neither do upright sword-shaped leaves alter their position, because in them both sides must be presumed to perform the same functions with respect to light as well as air.

Mr. Calandrini found vine-leaves turned to the light when separated from the stem and suspended by a thread. Of this any one may be easily satisfied, provided the experiment be made with sufficient care and delicacy. It is important, as demonstrating the turning to be accomplished by an impression made on the leaf itself, and not upon its footstalk.

Nor is this effect of light peculiar to leaves alone. Many flowers are equally sensible to