PLANT GEOGRAPHY 131 



crops grown with considerable difficulty owing to droughts, frosts 

 and other factors. 



Light. This is also an important factor which is very 

 generally recognized. Our attention has been called to the 

 fact that plants turn to the light and that their foliage is ad- 

 justed to receive the light to the best advantage. (Chapter IV.) 

 But a little careful observation will show us that while some 

 plants thrive best in the direct rays of the sun others are always 

 found growing in the shady places. It is now well known that 

 some of our agricultural crops thrive much better in the shade 

 than in the open. Coffee is very generally grown in the shade 

 of larger trees and many plants are grown in an artificial shade 

 produced by slat coverings or by large cheesecloth tents. 



These and many other factors of nature which influence the 

 spread of plants have given rise to that phase of botany known 

 as Plant Geography. 



PLANT GEOGRAPHY 



Plant geography is so closely associated with Ecology that 

 it is practically impossible to separate the two subjects by well- 

 defined boundaries. In our early study of geography we learned 

 that the earth was divided into five zones: Arctic, North Tem- 

 perate, Torrid, South Temperate and Antarctic, and we soon 

 learned to associate these zones with cold, temperate and hot 

 climates. But a little later we learned that countries in the 

 same parallels of latitudes did not necessarily have the same 

 temperature; mountainous regions in the torrid zone might 

 be cold as Iceland ; the Gulf current makes England much 

 warmer than points on our Atlantic coast which are much farther 

 south. It is very evident that elevations, mountains and water 

 barriers and the ocean currents exert very pronounced influences 

 on the temperature of a country and its plant growth. 



