24 University of California Publications in Botany [Vol. 9 



From the studies of J. E. Church*^ it appears that the densitj'- 

 of the snow-cover increases with altitude and method of deposition, 

 i.e., whether wind-laid or in sheltered drifts. At 8,000 feet in Jones 

 Pass on Mt. Rose, Church found a protected drift with a density of 

 26.6 ; at the summit (10,800 feet) a wind-laid deposit showed a density 

 of 39.5. The weight of the snow-cover mechanically influences the 

 growth-forms of high mountain plants. This weight increases as the 

 season advances and is greatest near the end of March, when melting 

 has begun to raise the water content of the snow. At Summit in 

 January, 1916, weighings made on the twenty-fourth and twenty- 

 seventh of different levels in a cover of 168 inches showed increasing 

 weights per cubic foot as follows : 



First cubic foot (surface) 10 lbs. 



Three feet from surface, cubic foot 14 " 



Six feet from, surface, cubic foot 18 " 



Ten feet from surface, cubic foot 22 " 



Bottom of cover, cubic foot 28 " ** 



In March the water content of the snow has greatly increased and 

 the bottom of the cover is a slush that weighs heavily upon the vege- 

 tation beneath ; in March, 1916, the cover was ten feet thick, the first 

 foot contained 56 per cent of water ; at the depth of five feet the snow 

 was 63 per cent water, and at the bottom, 66 per cent. 



In the boreal region snow conditions are complicated by several 

 factors : the diminished precipitation decreases the total snow ; the 

 usually bold relief favors the accumulation of drifts on lee sides of 

 peaks and crests but increases the power of wind to sweep large areas 

 bare ; the increased direct insolation plus the large amount of heat 

 reflected from the snow-fields below often causes the high peaks and 

 ridges to exhibit spring phenomena before the lower levels. 



The relative effect of protection from wind and sun is indicated 

 by certain measurements taken at Tahoe City (6,225 feet) in the 

 winter and spring of 1910 :*^ 



Treeless Meadow Pine-Fir Foresi Fir Forest 



Jan. 7 snow 24.6 inches 23.8 inches 25.0 inches 

 Jan. 19 41.6 " 40.4 " 



Mar. 11 29.8 " 31.4 " 30.4 " 



Mar. 21 20.0 "- 24.0 " 24.5 " 



Apr. 10-13 0.0 " Apr. 20 1.3 " Apr. 20 7.1 " 



At the beginning of the period the three types of surface had approxi- 

 mately equal amounts of snow ; at the end the meadow had been bare 



