62 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



resentative stations (Nos. 2, 3, and 7) are given. These, as pre- 

 sented, denote the average daily evaporation in cubic centimeters 

 for each observation period, reduced to the official standard main- 

 tained by the Laboratory of Plant Physiology of Johns Hopkins 

 University. The conclusions may be very simply stated. The high 

 rate of evaporation for the dry season and the low for the rainy 

 season are immediately evident. A rainless period in December 

 caused a sharp rise. The relative positions of the three lines are 

 maintained throughout the period of observation almost without 

 change, the Adenostoma habitats having the highest rates and the 

 forest the lowest. The absolute maximum attained was 51.4 c. c. 

 in station 2, Adenostoma chaparral, for the week ending September 

 19. This period included some of the hottest days recorded for the 

 region. The absolute minimum was attained on January 9, 3 c. c. 

 daily evaporation for the period of 6 days preceding. 



Evaporation 



R +* J To P °* Vegetation CUnity) 

 Katl ° V Surface of Ground 

 Dry Season Wet Season 

 49 days 114 days 

 June 8 to July 27 7 Nov. 10, 1913, to 

 1913 March 4, 1914 

 Sta. 2 Adenostoma 

 I J 



.53 



Arctostaphylos 



Forest 



J 



.69 



Fig. 16. — Ratio between evaporation at top of vegetation and at surface of ground, 

 in three representative stations at Jasper Ridge. 



In figure 15 the average daily evaporation for each station is 

 given, for both wet and dry seasons, readings from the upper series 

 of instruments being used. During the dry season the Adenostoma 

 stations have regularly the highest rates. Station 2, located on 

 the topmost point of Jasper Ridge, exposed to winds from every 

 direction, naturally has the highest of all. Stations 1, 4, and 5, 

 on gentle south-facing slopes, come next, and station 9, on the 

 steep south-facing slope of an abrupt ravine, is last, falling slightly 

 below the Arctostaphylos stations. The latter (stations 3 and 6) 

 are closely alike, and fall between the Adenostoma and the forest 

 stations, but nearer the former. The forest stations are decidedly 

 below the others. Evaporation during the wet season averages 

 about 30 per cent of the dry-season rate in the stations studied. 

 The figure also shows rates of evaporation during the most extreme 

 conditions of the year. The figure for station 8 seems abnormal. 



