A Comparison Between Two Mountain Sides. 137 



Greenland observation, - the daily light inaxi:.nu-.P- may be 

 reached about the sair.e tinie. As the sun disappears te.nper- 

 ature and moisture loss decline, and the day is considerably 

 shortened. On the west, little dew is left when the sun rises, 

 and the longer afternoon hours of sunshine contribute perhaps 

 considerably toward a warmer and drier day. But the soil on 

 both sides receives, daily, rays that are not far from the perpen- 

 dicular in mid-summer, and the number of hours of sunshine 

 are nearly the same. And, on the w^hole, the altitude is too 

 high to put much emphasis, as must be done in the desert, upon 

 the rigors of a long day as a limiting or directive factor of growth. 

 On the contrary, if it is true that growth takes place mainly at 

 night, as much of the inhibiting influence as may lie in tempera- 

 ture may be most active then, due to the low nocturnal tempera- 

 tures. 



In this connection may be given the results of comparative 

 data that were gathered on the temperature of the air and spring 

 water, and on precipitation, which it is hoped to give fully at 

 another time. Indicating here only the general trend, it was 

 found that the lowest nightly temperatures occurred on the west 

 side. Here, at Manning's Camp, the mercury first touched the 

 freezing point on October 6th, while at the eastern station, at 

 Miller's Cabin, only 500 feet (150 m.) lower, and two miles distant, 

 it had not fallen below 40° by the 24th. For a number of fair 

 days in the m.iddle of October the minima on the west ranged 

 from 32° to 38° F., while the same days on the east showed 48 - 

 56° F. During the same period the maxima for the west side 

 read from 57° to 67° F., while those on the east show- a range 

 of 56°-62°. The western station is therefore both slightly warm- 

 er in davtime and decidedlv colder at night, and it is indicated 

 that the two mountain sides possess a markedly different daily 

 range of temperature. 



While these data were taken at a date when the growing 

 season was practically over, there is nothing to indicate that 

 similar differences do not hold throughout the growing season. 

 In fact, in the latter part of August, this being near the height of 

 the vegetative season, a common maximum range at the eastern 

 station was 15° or 16° F., while but a few days later a daily 

 range of 33° was frequently reached on the west. On the desert 



♦Drude, Pflanzengeog, p. 20, 1890. 



