358 EXPERIMENTS WITH PLANTS 



of the same devices for preventing evaporation which 

 we have seen in desert plants : the strong light, rare- 

 fied air and the constant winds tend to promote 

 evaporation, while the coldness of the ground hinders 

 absorption. 



Owing to the short time which such plants have 

 for flowering and fruiting, they perform these opera- 

 tions very rapidly, often in half the time needed by 

 similar species in the lowlands. 



The plants of northern latitudes resemble alpine 

 plants in most respects, and especially in the last- 

 mentioned feature, i. e., early -flowering and fruiting. 

 Gardeners take advantage of this to get early varie- 

 ties by importing seed from northern regions. Some- 

 times seed is sent to such regions to be grown until 

 the desired earliness has been obtained. 



Of the plants familiar to you, which are most sensi- 

 tive to cold? which are least sensitive ? Do you find 

 differences in individual branches of the same tree in 

 this respect f 



In view of the facts which we have just discussed, 

 we may realize vividly that the life of every plant is a 

 continual and delicate adjustment to its surroundings. 

 Some plants possess the power of adjustment to a 

 greater degree than others; but all must exercise it 

 constantly in order to survive; and this is a funda- 

 mental characteristic of all living organisms. 



We may illustrate this further by considering a tree. 



