1916] Dice: Land Vertebrates of Southeastern Washington 325 



The growing season of southeastern Washington is comparatively 

 long. At Prescott it is often possible to plant the seeds of hardy vege- 

 tables in the open ground in the first week of March or earlier. The 

 frostless season is also comparatively long (Table 3), although irregu- 

 lar frosts late in spring often do considerable damage to fruit and 

 garden crops. 



TABLE III 

 FROST DATA 



Columbia Basin sagebrush area Columbia Basin prairie area 



Station Kennewick Touchet Walla Walla Dayton 



Length of record 7 5 23 5 



Average date first frost in 



Autumn Oct. 15 Sept. 13 Nov. 3 Oct. 13 



Average date last killing 



frost in Spring Apr. 28 Apr. 23 Apr. 1 Apr. 25 



Earliest date of killing frost 



in Autumn Sept. 25 Aug. 25 Sept. 28 Sept. 23 



Latest date of killing frost 



in Spring May 25 May 8 May 3 May 8 



Average season between 



frosts days 170 143 216 171 



Frostless season days 123 109 148 138 



No records of humidity are available from the various habitats of 

 Walla Walla and Columbia counties, but in Whitman County, Wash- 

 ington, and in the Thatuna Hills of Idaho, Weaver (1914) has ob- 

 tained records of the rate of evaporation as determined by a porous- 

 cup atmometer during the summer. These records show that the rate 

 of evaporation is highest in the rocky-slope habitat and that in the 

 other habitats it decreases in the following order: prairie, S.W. ex- 

 posure ; prairie, N.E. exposure ; yellow pine ; fir-tamarack ; cedar. The 

 sagebrush habitat was not included in these observations. 



The prominent features of the climate of the sagebrush area is the 

 small annual precipitation and the high temperature of summer. No 

 records of wind velocities are available from these stations, but it is 

 known that the area is subject to strong winds which act powerfully to 

 drift the sandy soil. 



The prairie area as a whole shows a lower average temperature and 

 particularly a lower temperature in the summer months than is found 

 in the typical part of the sagebrush area as recorded at Kennewick. 

 Also the prairie area shows a greater rainfall and this rainfall is 

 greater the more closely the Blue Mountains are approached. It may 



