58 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



The maxima during the dry season would often be considerably 

 higher than those recorded here. Even in winter the day tem- 

 peratures are frequently quite high. Frosts are rare and slight. 

 During the winter of 1913-14 no atmometers were broken from this 

 cause — and these instruments are very sensitive to that danger. 



Table 10. — Atmospheric temperature. 



Wind. 



I have no data for Jasper Ridge, but a statement as to the sur- 

 rounding region as a whole will be of value. Throughout the Santa 

 Cruz Peninsula and northern Santa Clara Valley, except where 

 topography produces local differences, the prevailing direction of 

 wind is northwest. During the dry season this is almost universally 

 true. During the wet season the direction is much more variable. 

 Northwest winds are still the commonest, but the severe storms 

 that bring the rains are usually accompanied by gales from the 

 southwest. The north-facing slopes, therefore, receive most of the 

 dry summer winds, while the south-facing slopes receive the full 

 force of the rain-bearing winter gales. That the former may be 

 very severe in their effects I have shown in another paper (23, 

 p. 187). The actual vegetation cover of the north- and south- 

 facing slopes is evidence that in general the prevailing winds are 

 not important as locally controlling factors. 



The Atmospheric Moisture. 



Rainfall, cloud, and jog. — These topics have already been treated 

 (p. 31). They are of interest in consideration of the locality as 

 a unit, but have little influence upon the distribution of the plant 

 communities as determined by slope exposure. 



Relative humidity.— The effects of relative humidity upon veg- 



