126 THE FITNESS OF THE ENVIRONMENT 



obscure, and in any case there seems to be 

 no immediate hope of bringing them into 

 connection with the science of biology. 



C 



SURFACE TENSION! 



Of all common liquids, except mercury, 

 water has the greatest surface tension. 



Table of Surface Tensions 



Water 75 



Carbonic acid 1.8 



Ammonia 41.8 



Mercury 436 



Benzene 28.8 



Methyl alcohol 23 



Ethyl alcohol 22 



Ether 16.5 



Glycerine 65 



Acetone 23 



Formic acid 37.1 



Acetic acid 23.5 



Chloroform 26 



This fact is of enormous moment in biology, 

 most obviously perhaps in its influence upon 

 the soil. For surface tension and density 

 determine the height to which a liquid will 

 rise in a capillary system, and thus it comes 

 about that the principal factor in bringing 

 water within reach of plants is the exceptional 

 surface tension of water. The nature of the 

 case is clearly explained by Hilgard. "The 



