26 



ANIMAL LIFE IN DESERTS 



this figure is based on average readings for that 

 period, and the fluctuation would be even more 

 remarkable were figures available, not from Moham- 

 merah itself, which is on the Karun River among 

 date palms, but from a spot two or three miles from 

 it in bare desert country. 



Relative humidity varies very greatly within very 

 short distances. Observations taken among a few 

 palms, or in a cave or house, show a humidity 

 very much less variable and generally higher than 



6?..n. 8ajii lOam. IZfwon Zptm. 4 p.m. 6p.m. 



Fig. 9. — ^Mean Relative Humidity at Two -hourly Intervals for the 

 Months June, July, August, and September at Mohammerah, 

 Persian Mesopotamia. 



that which is prevailing a few yards away in open 

 desert. 



It is generally true that the greatest fluctuations 

 in relative humidity occur during summer, and this 

 depends largely on the fact that the temperature 

 fluctuates more during a summer day than a winter 

 day (page 19). Rapid and wide alterations in the 

 relative humidity are therefore one of the many 

 chmatic factors which combine to attack both plants 

 and animals in summer, in deserts. 



