3 8 A Study of the Vegetation of 



termine the relation between this factor and succession. Read- 

 ings at depths of 2 and 10 inches respectively, were taken at the 

 same stations and at the same time that soil samples for moisture 

 determinations were secured. In addition to these a large number 

 of readings near the soil surface, in the soil surface, and at depths 

 of one and two feet respectively, were made from time to time. 

 Many of the temperature readings were made simultaneously, and 

 in all cases recorded the interval between the readings at the 

 various stations was so short that the error thus introduced is 

 almost negligible. This possible error was further reduced by 

 taking the readings in the various habitats at any set of stations in 

 varying sequence. 



An examination of these data shows almost uniformly a de- 

 crease in soil temperature as the climax communities are ap- 

 proached. The following tables, selected as representative from 

 these data, are illustrative : 



TABLE V 



SHOWING THE RELATION OF SOIL TEMPERATURE TO PLANT SUCCESSION 

 Coljax, Wash., 



* Readings taken at a depth of 4 inches. 



38 



