THE SOIL AND WATER 



121 



Light. More water is transpired in the light than in darkness. 

 For example, Deherain 1 determined the water evaporated per 

 hour and 100 grams of leaf, to be as follows: 

 WATER EVAPORATED. 



On the other hand, excess of light may diminish transpiration. 



Composition of the Soil or Solution. The solution brought in 

 contact with the roots or stem of a plant exerts a decided influence 

 upon the amount of water transpired. According to Burger- 

 stein, 2 small quantities of acid added to distilled water increase 

 transpiration, alkalies retard it, and the effects of salts depend 

 upon the nature and concentration of the solution. With single 

 salts, transpiration increases with the concentration of the solu- 

 tion, until a maximum is reached. The effect of mixtures of two 

 or more salts depends upon the nature of the salts used. Of 

 greater agricultural importance is the fact that a complete nutri- 

 tive solution decreases transpiration. The following table gives 

 some examples : 



The fertility and nature of the soil also appear to exert an 



1 Jahresber. f. Agr. Chem., 1868, p. 273 

 * Jahresber. f. Agr. Chem., 1875, p. 388. 

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