22 University 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 shrubs, 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 plays 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 inclusive. 



Nov. 189 06 032 034 



Fordyce Dam Dec. 9 28 39 35 60 74 



Nevada County Jan. 40 75 85 69 15 100 8 161 



6,500 feet Feb. 86 91 103 9 158 27 157 44 154 



Mar. Ill 108 103 45 165 58 154 67 154 



47 32 



70 32 



26 178 2 218 



27 240 23 215 

 38 276 50 262 



55 29 



101 8 125 



25 178 20 274 



45 407 42 434 



79 440 62 338 



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 m'ajority of years, a light 



