224 BOOKS AND CURRENT LITERATURE 



irrigation might be predicted by this method of testing leaves, long 

 before wilting is evident. 



Probably the most valuable point brought out in this article, and 

 certainly the most interesting one to ecologists, relates to an ecological 

 classification of plants based upon foliar transpiring power as shown by 

 this method. The diurnal transpiring powers were determined for a 

 large number of plants growing under irrigation. Plants which are un- 

 questionable mesophytes exhibited indices of diurnal foliar transpiring 

 power of 0.70 or higher, while all plants exhibiting similar indices of 

 0.30 or less would be pronounced xerophytic without hesitation, on the 

 basis of simple observation. Although much more work must be done 

 before a relative scale of xerophytism or of mesophytism can be erected, 

 this preliminary study makes it certain that the method here employed 

 offers a simply applied means for an ecological classification based upon 

 quantitative measurements. Drought resistance in cultivated crops, 

 in S3 far as water withholding capacity is concerned, can also be meas- 

 ured by this method, as Bakke shows by experiments upon two very 

 different varieties of alfalfa and upon two forms of Sorghum halepense, 

 Johnson grass, and Sudan grass. Further work in this direction should 

 prove very interesting and valuable for economic purposes. 



The paper here reviewed merits the attention of those engaged in 

 studies in pure physiology, as well as of those investigating plants in 

 the field, from either the agricultural or ecological point of view; the 

 method seems to be very promising. — Samuel F. Trelease. 



