CHAPTER III 



THE PLANT AS AFFECTED BY UNFAVORABLE 

 ENVIRONMENT 



181. Factors of Environment. The plant environment 

 is mostly comprehended under the terms, climate, soil, 

 animals and other plants. But as these are more or less 

 complex influences, it is well to analyze them and to con- 

 sider separately the component factors of each. 



SECTION I. THE PLANT AS AFFECTED BY UNFAVOR- 

 ABLE TEMPERATURE 



A THE PLANT AS AFFECTED BY EXCESSIVE HEAT 



182. Transpiration Increases with the Degree of Heat. 



The most common effect of heat upon plants is the droop- 

 ing 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 sufficient 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 as to appear dead, but unless the 

 heat has been sufficient to destroy their protoplasm, or 

 the heated period has been protracted, they will recover 

 when normal temperature and water supply are restored. 



(115) 



