Cannon : Transpiration of Fouquieria 401 



at night-time exceed 28 per cent. In the daytime it was always 

 low (figure 2). 



A certain peculiarity of the changes in the relative humidity, 

 which may have to be taken into account when the biological 

 significance of the absorption of water by the aerial parts is con- 

 sidered, may be pointed out. I refer to the fall of the humidity 

 which ordinarily occurs soon after a storm has passed. This is 

 illustrated in figure 3. On Wednesday night, Thursday and 

 Thursday night a small rainfall (.04 in.) occurred. During the 

 rain the humidity was rather high even in the laboratory where 

 the hygrograph was placed, but within twelve hours after it ceased 

 the humidity w^as nearly as low again as previous to the storm. 



The humidity remains high, however, for several days follow- 



* 



ing a long storm, and since the most rain ordinarily falls in sum- 

 mer this peculiarity cannot fail to be of great importance to the 

 desert plants. 



As regards the temperature it will not be necessary for the 

 present purpose to go into this phase of the climate of the year 

 more than to mention certain striking characteristics. 



The annual as well as the daily range was relatively large. 

 During the driest portion of the summer, in June, the maximum 

 for the year, 107° F., was recorded. The temperatures were 

 somewhat lower after the rains of summer had come. (See fig- 

 ure I, which shows the mean maximum temperature for 1904.) In 

 the colder part of the year, December to March, the thermometer 

 reached the freezing point or below each month, and in January a 

 temperature of 15° F., which was the minimum for the year, was 

 reported. The range of temperature for the year was therefore 



92° F. 



Fifty degrees Fahrenheit was the greatest daily range. This 

 was recorded in April in the midst of a rainless period. In Au- 

 gust, on the other hand, during the summer rains, a daily range of 

 but 31° F. was noted — this was the least of the year. 



Fouquieria splendens 



Fouquieria splendens, " ocotillo" of the native Mexicans, is 

 one of the most striking desert shrubs. It is well adapted, not 

 only in the mature condition b.ut as a seedling as well, to endure 



