16 



but the writer does not believe that in case the period had been longer 

 the general results would have been different, since the investigation 

 extended over the most critical season of the year, namely, the part of 

 the summer when the evaporation rates are relatively high and soil 

 moisture relatively low; and these are the most critical conditions 

 for the development and survival of plants. 



ACKNOWIvEDGMENTS 



Grateful acknowledgment is here extended to Dr. H. C. Cowles, 

 of the University of Chicago, for suggesting the problem and site for 

 study; to Mr. and Mrs. McLeish for their kindness in permitting 

 weekly visits to their estate, on which the ravine is located ; to H. 

 DeForest for photographs of vegetation in vicinity of stations, and to 

 Dr. Geo. D. Fuller, also of the University of Chicago, for his helpful 

 suggestions in overcoming the difficulties that arose in the course of 

 the investigation. 



LiTKRATURB CITED 



Atwood, Wallace W., and Goldthwait, James W. 



'08. Physical geography of the Evanston-Waukegan region. 

 Bull. 7, State Geol. Surv. 111. 



Briggs, L. J., and Shantz, B. L. 



'12. The wilting coefficient for different plants and its indirect 

 determination. Bull. No. 230, Bur. of Plant Industry, U. S. 

 Dept. Agr. 



Brown, Wm. H. 



'10. Evaporation and plant habitats in Jamaica. Plant World, 

 13 : 268-272. 



Cowles, H. C. 



'01. Plant societies of Chicago and vicinity. Bull. No. 2, Geogr. 

 Soc. Chicago. 



Fuller, Geo. D. 



'11. Evaporation and plant succession. Bot. Gaz., 52: 193-208. 



Livingston, B. E. 



'01. Operation of the porous-cup atmometer. Plant World, 



18: II 1-119. 

 '13. The resistance offered by leaves to transpirational water loss. 

 Plant World, 16: 1-33. 



