58 ANIMAL LIFE IN DESERTS 



the deserts of America there are two rainfalls : that 

 which occurs in December and January is followed 

 by crops of flowers of winter annuals: as soon as 

 the cold weather is passed : these then dry up and 

 perish. The summer rains come and soak the ground, 

 but the seeds of the winter annuals do not germinate ; 

 instead, there comes up a crop of summer annuals 

 which ripen seed soon after midsummer ; this seed 

 lies dormant all through the cold weather, even 

 though it is saturated by the winter rains. Whether 

 the desert has one rainy season or two these annual 

 plants add very greatly to the number of species 

 and of individual plants occurring in an area ; in 

 fact, a richness of flora is produced which for the 

 moment far exceeds the inroads made upon it by 

 the larger herbivorous animals : their number is 

 Umited by their abiUty to exist through the long 

 dry seasons. The smaller forms of animal Hfe, for 

 instance, the insects, increase in numbers enormously 

 as the annual vegetation grows, and Uke it rest in 

 various ways for the rest of the year. 



The second large biological group contains plants 

 which exist beneath the ground during the dry 

 months in a dormant condition, and which produce 

 leaves, stems, and flowers after rain has fallen. The 

 perennial part of the plant is a bulb, corm, tuber, or 

 fleshy root. It is essentially an organ for storing 

 food, and it is by drawing upon these reserves that 

 the plant is able to respond rapidly to rainfall and 

 send up its flowers and leaves : there is no occasion 

 for the storage of water, for these plants are active 

 only at a season when water is abundant. Plants 



