. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 128 BOTANY tend to droop or fold after a much shorter exposure to the dark ness. These changes in position have been called sleep move- ments. Charles Darwin suggested that the leaves of a plant which take this position secure protection from injury by frost. In most cases the movement may be accounted for when we remem- ber that leaf blades naturally turn their upper surfaces toward the light. In the absence of light the leaf blade might easily be in- fluenced to droop or even fold by the
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 128 BOTANY tend to droop or fold after a much shorter exposure to the dark ness. These changes in position have been called sleep move- ments. Charles Darwin suggested that the leaves of a plant which take this position secure protection from injury by frost. In most cases the movement may be accounted for when we remem- ber that leaf blades naturally turn their upper surfaces toward the light. In the absence of light the leaf blade might easily be in- fluenced to droop or even fold by the counter stimulus of gravity. Sensitiveness to Contact. — Leaves of some plants are also sensi- tive to the stimulus of contact. The sensitive plant (Mimosa pudica) is the best-known example. Here the leaflets of the com- pound leaf respond to the slightest touch by folding and drooping. Under normal conditions the leaf soon returns to its original posi- tion. Changes in temperature and moisture may totally prevent this movement, showing that the living matter in the plant is most delicately attuned to the influences of its immediate surroundings. The Sun a Source of En- ergy. — We all know the sun is a source of most of the energy that is released on this earth in the form of heat or light. Solar engines have not come into any great use as yet because fuel is cheaper. Actual experiments have shown that vast amounts of energy are given to the earth. When the sun is in the zenith, energy equivalent to one hun- dred horse power is received by a plot of land twenty-five by one hundred, the size of a city lot. Plants receive and use much of this energy by means of the leaves. In which Part of a Variegated Leaf does Starch Exist P — Leave two plants, such as the Coleus (variety with red-colored leaves) or Tradescantia (the white-striped leaf variety) and another Coleus or Tradescantia with the. A hydrangea plant, upon the leaves of which disks of cork have been pinned in order
Size: 1524px × 1639px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., boo, bookpublishernewyorkamericanbookcompany, booksubjectbiology
