340 Introduction to Botany. 



rainfall averages less than 20 centimeters yearly, lie within 

 this region. A large part of western Europe and of 

 eastern North America has a rainfall of 60 to 130 cen- 

 timeters, while in some of our Southern states, and in parts 

 of Europe, the precipitation ranges between 130 and 200 

 centimeters annually. 



The low winter temperature of the greater part of the 

 temperate zones precludes the presence of many plants 

 which are at home in the tropics, but which have thus far 

 been unable to adapt themselves to low temperatures. 

 Thus palms, bamboos, bananas, etc., do not venture far 

 outside of the tropics, but in their stead we find pines, firs, 

 spruces, and other conifers, and forests of oaks, hickories, 

 walnuts, and beeches, which in the tropics have represen- 

 tatives, as a rule, only in the mountains. How the tropical 

 and temperate forms mingle in the southern part of the 

 north temperate zone is shown by Fig. 184, which repre- 

 sents dwarf sabal palms and pine trees occupying the same 

 ground. In Florida and Louisiana the boughs of forest 

 trees are often bedecked with luxuriant growths of Tilland- 

 sia usneoides, an epiphyte which is also native to tropical 

 forests (Fig. 185). 



The effect of the amount of annual rainfall on the char- 

 acter of the vegetation in the temperate zone may be seen 

 as one passes across the United States from east to west. 

 Along the Atlantic and Gulf coasts the rainfall, amounting 

 to more than 100 centimeters annually, is distributed 

 throughout the year, with the maximum amount in summer. 

 The rainfall gradually diminishes toward the west, until at 

 the Mississippi River the annual amount is about 60 centi- 

 meters. Along the coasts, and in the mountains of the 

 Atlantic states, the rainfall being sufficient to keep the soil 

 moist at considerable depths, forest trees abound, so that 



