46 



H. B. HUMPHREY AND J. E. WEAVER 



by September 5. The wilting coefficient of this soil free from 

 rocks is 10%, and. records show that after July 20 of 1913 no 

 moisture was available in the first 25 cm. of soil. During the 

 whole period from May 10 to September 5 the average daily 

 evaporation was 24 cc. and during the week ending August 29 it 

 ran as high as 44.8 cc. daily; and still the seedlings were not 





Fig. 9. The northeast side of the same butte shown in Figure 8. Douglas 

 fir and tamarack are the chief components of this forest. 



killed! In fact the soil mulch of needles and the shade afforded 

 by the parent trees kept down the evaporation considerably both 

 from soil and air, as compared with a prairie station a few meters 

 lower down the mountain slope. 



2 Weaver, John Ernst, Evaporation and Plant Succession in Southeastern 

 Washington and Adjacent Idaho. The Plant World, 17: 273-294, 1914. 



