Ch. Ill, 6] TRAXSPIRATIOX FROM PLAXTS 



47 



ing the question as to the 

 relation between the two 

 processes. While closely 

 related, they are not iden- 

 tical, as shown by the 

 modem studies on rela- 

 tive TRAXSPIRATIOX, that 



is, the ratio between tran- 

 spiration and the contem- 

 poraneous evaporation, as 

 determined by suitable in- 

 struments. In brief, tran- 

 spiration is evaporation 

 affected considerably by 

 the structm-e and physi- 

 ologj' of the leaf. 



The profound effect of 

 external conditions upon 

 transpiration has many 

 important consequences. 

 Thus, a conjunction in 

 high degree of light, heat, 

 drjTiess, and ■ndncls, as 

 happens at times in our 

 gardens, can cause wilting 

 in some plants even when 

 the}' have ample soil 

 water, because the roots 

 cannot absorb, or the 

 stems conduct, water as 

 fast as transpiration re- 

 moves it. In such cases 

 a check in the transpira- 

 tion, by the coming of 

 night or a spraying by the 

 gardener, is promptly fol- 



