22 



Universiti/ of California Publications in Botany [Vol. 9 



At Summit, during a period of thirty-five years, July was the only 

 month with no snow. August showed only a trace in one year. The 

 snow season begins in September but, throughout that month and the 

 next, snow melts as fast as it falls, the snow-cover not appearing till 

 the first week in November. This appearance of the ground-cover 

 normally marks the beginning of winter and the complete cessation 

 of the vegetative period — at least for herbs and low shrvibs, as its dis- 

 appearance marks the beginning of the local "spring" for these 

 plants. The cover increases to a maximum in March when melting 

 becomes dominant and thereafter the snow-cover diminishes steadily 

 to zero in the first ten days in July (table 5). 



The snow-cover plaj^s such an important part in the biology of 

 the high mountain region that its fluctuations are of considerable 

 moment. The graph presented in table 5 shows the normal accumu- 

 lation and dissipation of the snow-cover at Summit. The data given 

 below show the average condition of the surface, at the first, middle, 

 and end of each month, from the beginning of the snow season to the 

 snow maximum in March, and, at the right, the varying condition of 

 the surface observed once or oftener on the same dates (data in 

 inches). Period, 1906-07 to 1917-18 inclvLsive. 



Summarizing the data for this element of the high mountain 

 habitat, we note that on the first of November, at all three stations, the 

 ground may either be bare of snow or may already have received the 

 beginning of the snow-cover. At all' three places in the majority of 

 years, the ground has not yet received its winter blanket by November 

 first. By the middle of November, in the majority of years, a light 



