CHAPTER III. 



THE PLANT AS AFFECTED BY UNFAVORABLE 

 ENVIRONMENT. 



180. Factors of Environment. The plant environ- 

 ment is mostly comprehended by 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 consider separately the component factors of 

 each. 



Section I. The Plant as Affected by Unfavorable 

 Tempeeatuee. 



A — The Plant as Affected by Excessive Heat. 



181. Transpiration Increases with the Degree of 



Heat. The most common effect of heat upon plants is 

 the drooping of the foliage, due to excessive transpira- 

 tion (74). 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 tempera- 

 tures, transpiration may be so much increased by an 

 overheated atmosphere that the roots are unable to sup- 

 ply the plant with sufficient water, hence the cells be- 

 come partially emptied and the foliage droops. Her- 

 baceous 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 suffi- 

 cient to destroy their protoplasm, or the heated period 

 has been protracted, they will recover when normal 

 temperature and water supply are restored. 



(118) 



