40 ANIMAL LIFE IN DESERTS 



commoner different types of soil of which the desert 

 may consist, and the various problems which have 

 to be faced by organisms which inhabit the sand, 

 or gravel, or rock, or mud. 



The sand is in many ways the most hostile of 

 all environments. Its surface is very smooth, and 

 offers little impediment to the wind. As has 

 been said already, winds in any desert tend to be 

 strong, sometimes violent : in sandy desert their 

 action is unchecked by any obstacle. These winds 

 are detrimental to the plants ; they break leaves 

 and branches, they greatly increase evaporation 

 from the soil and transpiration from the plant, 

 and they carry abrasive particles of sand and soiL 



As the surface of most sandy areas is frequently 

 in motion, even in the absence of sand-storms, it 

 is extremely difficult for plants to colonize them. 

 Young seedlings are overwhelmed, tender shoots 

 are damaged by blown sand, and roots are laid bare 

 to the sun. In certain places where the surface of 

 dunes is particularly unstable no vegetation of any 

 sort grows. In the Indian deserts, according to 

 Blatter and Halberg, the fairly copious monsoon 

 rains may temporarily consoUdate the surface of a 

 dune which at other seasons is unstable. SeedUngs 

 of various plants then spring up and, as the sand 

 dries, some individuals of certain species hold their 

 own, while the rest die. In all parts of the world 

 spots which are less wind-swept are colonized by 

 special plants, many of them grasses, which re- 

 semble the marram of our own coasts in their habit, 

 and after they have established themselves and to 



