GENERAL SUMMARY AND CONCLUSIONS. 69 



ENVIRONMENTAL FEATURES OF THE FLORA OF ALGERIA. 



The physical en\'ironment of the plants of southern Algeria is, in a few 

 broad features, similar to that of the southwestern portion of the United 

 States. These regions have about the same latitude, both are separated 

 from a large sea by mountains, and the range in altitude is similar. There 

 are other features, however, particularly as regards the amount and the 

 distribution of the precipitation, in which the two widely separated regions 

 are very unlike, and a correlated difiEerence in the habit and composition 

 of the floras of the two regions is apparent. 



The Algerian climate as a whole is a mild, temperate one, but very 

 diverse. The latitude and topography taken in connection with the 

 presence of large seas to the north and west, and a large continent leading 

 away to the south are its chief determinants. The climate, therefore, of 

 the northern portion is coastal; that of the southern portion continental. 



Probably the most important of the secondary factors which modify the 

 climate of Algeria is its highly varied topography. An important moimtain 

 system, the Atlas, made up of many more or less detached groups and 

 secondary systems, a plateau or steppe lying 3,000 feet more or less above 

 the sea, and finally the northern edge of the Sahara, which has a very 

 diverse topography of its own — such is the surface of Algeria. 



Algeria is divided into three climatic provinces corresponding to the 

 leading topographical differences: the Tell, including the littoral, or por- 

 tion between the maritime Atlas and the Mediterranean; the High Plateau, 

 or steppe, which lies between the Tellian Atlas and the Saharan Atlas ; and 

 the desert. These provinces have marked individual differences in rain- 

 fall, temperature, and other climatic features. 



In the Tell and the High Plateau the winds from the sea deposit most 

 of their moisture. Along the coast as much as 700 mm. of rain is recorded, 

 while in other parts of the Tell it is about 570 mm. On the High Plateau the 

 yearly precipitation sinks to 310 mm. In the desert south of the Saharan 

 Atlas, however, where the altitude is lower and the temperature greater 

 than in either of the other provinces, the yearly rainfall is 200 mm. and less. 

 In some years, in fact, no precipitation whatever is reported in the desert. 



The seasonal distribution of the rains in any arid or semi-arid region is 

 of great importance as a factor in shaping the character of the vegetation. 

 For example, in the semi-arid region of the southwestern part of the United 

 States, in the Tucson region, there are two distinct rainy seasons — the rains 

 of winter and those of summer — and here the plants T\ith a water-balance 

 are an important feature ; but farther to the west, where there are no summer 

 rains, there are no succulents. In Algeria, also, there is but one rainy season 

 and it has already been noted that the absence of plants with water-storage 

 facilities is one of the leading characteristics of its vegetation. The seasonal 

 distribution of rains is as follows: In the Tell, in winter it is 42 per cent. 



