SECTION III 



TEMPERATURE RELATIONS OF 

 FRUIT PLANTS 



Of the four great factors of plant environment, moisture, soil, light 

 and temperature, the fruit grower can modify two considerably. He 

 can irrigate or drain, he can fertilize, if necessary; he can, to some extent, 

 modify soil texture; light and temperature he must take as they come. 

 The object of the present section is to indicate how, though temperatures 

 cannot be changed, except in certain minor respects, fruit growing can be 

 modified to capitalize favorable temperatures or to minimize the unfav- 

 orable effects. Knowing the various effects of heat or its lack the grower 

 is able to chose fruits best adapted to existing conditions, to avoid 

 attempting the impossible or the very hazardous, to pick favorable 

 sites and so to manipulate his plants that they will have the best possible 

 adjustment to the various temperature conditions of their environment. 



Temperatures influence plants in several ways bearing directly on 

 fruit growing: (1) they delimit zones beyond which the growing of specific 

 fruits becomes commercially hazardous because of low winter tempera- 

 tures; (2) they delimit zones beyond which the growth of certain fruits 

 becomes unprofitable because of high summer temperatures; (3) they 

 make certain areas unprofitable for some fruits because of low summer 

 temperatures; (4) they render much good land of doubtful value for 

 several fruits because of danger from spring frosts; (5) within areas ordi- 

 narily safe for growing certain specific fruits an occasional deviation 

 from normal may cause considerable damage; (6) some insects and 

 diseases are more or less dependent on proper temperatures for their 

 optimum development. 



Lest this statement should give an unpleasant connotation to tem- 

 perature relations, it should be stated conversely that these very limita- 

 tions predicate the presence at some places of temperatures favorable 

 to fruit growing. The existence of fruit growing at all is obvious proof. 

 Unfortunately attention is centered rather on the Umitations, so that, 

 though many unfavorable conditions are fairly closely understood, 

 optimum temperatures for the various fruits are not defined so clearly. 



Schimper,^^* commenting on the difficulty of temperature investigations, 

 states: the "existence of such action on vegetable organisms is less clearly 

 recognizable than is that of water. We can directly observe the ingress of water 

 into a plant and its egress, we can explain physiologically the effects caused by 



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