78 



intense dryness, in which every motion stirs up a copious, fine, 

 penetrating dust which keeps one covered as long as he remains 

 in it. At this time, the landscape is almost unvaryingly bare 

 and of various shades of gray, brown and red. Flowers are 

 almost wanting, although this is a favorite blooming time with 

 many cactuses, and there are some other succulents, such as 

 jatrophas, which then begin to bloom. 



Not only does the period of rains differ greatly in different 

 parts of this arid region, but the amount of rain shows remarkably 

 wide limits of variation. Even where there is but little, a 

 surprising change occurs in the aspect of the country after its 

 occurrence. Within a month, the ground acquires a more or 

 less nearly complete covering of grasses and is carpeted in 

 patches, often large ones, with solid masses of bloom, and the 

 appearance of the surface is abundantly broken by patches of 

 flowering shrubs. 



The most conspicuous objects on these plains are yuccas, 

 agaves, fiat and cylindrical jointed opuntias, covilleas, Proso- 



FiG. I. The Balsas River. 



pis, and artemisias. The opuntias grow almost everywhere, 

 yuccas of some species are almost as generally distributed, 



