456 A TEXTBOOK OF GENERAL BOTANY 
evergreen leaves; while still others are deciduous and have 
mesophytic leaves during the rainy period. 
The appearance of deserts varies greatly according to the kinds 
of plants found in them. In many places the plants are largely 
shrubs (Fig. 513), while in other regions succulents are con- 
spicuous (Figs. 512, 514). In parts of the American desert cacti 

Fria. 512. Arizona desert with large Opuntia 
predominate, while in parts of Africa, particularly in the south, 
there are numerous euphorbias with a general appearance similar 
to that of certain cacti. 
The appearance of deserts also changes according to the 
seasons; during a dry period the vegetation is very scanty and 
has a gray or rather dirty green color, while in the rainy period 
the vegetation is much more luxuriant, owing to the presence 
of the annuals and of the mesophytic foliage on the deciduous 
perennials. At the same time flowers are frequently found to be 
very numerous. 
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