BOTANICAL GEOGRAPHY 325 



regions very abundant (over sixteen feet of rainfall in a 

 year) or sometimes, in desert areas, almost lacking. We 

 find here, accordingly, the greatest extremes in amount 

 of vegetation, from the bare sands or rocks of the Sahara 

 desert (Fig. 229) to the densely wooded basin of the 

 Kongo and of the Amazon. Xerophytic plants, many of 

 them with extremely complete adaptations for supporting 

 life for long periods without water, are characteristic of 

 tropical deserts, while many of the most, decided hydro- 

 phytes among land-plants are found in the dripping sub- 



FIG. 229. Hills of Drifted Sand in the Sahara. 



tropical forest interiors. Throughout a large part of the 

 zone, reaching five degrees each way from the equator, 

 there are daily rains the year round. 



397. Vegetation of the Temperate Zones. We are all 

 familiar in a general way with the nature of the plant 

 life of the north temperate zone ; that of the south 

 temperate is in most ways similar to our own. Most of 

 the annuals and biennials are of a medium type, not 

 decided xerophytes nor hydrophytes, and the perennials 

 are mainly tropophytes. There are no desert areas so 

 large or so nearly destitute of plants as those found in 

 subtropical regions, neither are there any such luxuriant 



