CHAPTER IIL. 
THE PLANT AS AFFECTED BY UNFAVORABLE 
ENVIRONMENT 
181. Factors of Environment. The plant environ- 
ment is mostly comprehended under the terms, climate, sovl, 
animals and other plants. But as these are more or less 
complex influences, it is well to analyze them and to consider 
their component factors separately. 
Section I. Tur PLANT AS AFFECTED BY UNFAVORABLE ~ 
TEMPERATURE 
A —TuHeE PLANT AS AFFECTED BY EXcESSIVE HEAT 
182. Transpiration Increases with the Degree of 
Heat. The most common effect of heat upon plants is the 
drooping of the foliage, due to excessive transpiration (75). 
With insufficient water, this may occur at a temperature that 
is normal for the plant. But with a water supply that is 
sufficient at ordinary temperatures, transpiration may be so 
much increased by an overheated atmosphere that the roots 
are unable to supply the plant with water, and as the result, 
the cells become partially emptied and the foliage droops. 
Herbaceous plants in an overheated greenhouse or hotbed 
are sometimes so prostrated from excessive loss of water 
from their tissues as to appear dead. But unless the heat 
has been sufficient to destroy their protoplasm, they will 
recover when their normal temperature and water supply 
are restored. | 
