GROWING SEASON TEMPERATURES 241 



Acclimatization to Varying Amounts of Heat. — It is conceivable that 

 through acclimatization plants graduallj^ may require more or less heat 

 for a given function; evidence to this effect is cited by Bailey.^ Cuttings 

 of Concord grape from Maine, central New York and southern Louisiana 

 planted simultaneously under uniform conditions at Ithaca, N. Y., made 

 in a given time the following respective growths: 2.66 inches, 1.6 inches 

 and 1.3 inches. The seed potato trade of ]\Iaine is founded on the quick- 

 ened response to a given temperature by potatoes grown there. Data 

 already cited in this chapter show a tendency for plants in northern 

 sections to attain a given stage of development with less heat than in 

 southern sections. Elsewhere it is shown that plants accommodate them- 

 selves to a wide range of moisture, nutrient and light conditions; there- 

 fore it is not surprising that they show a corresponding adaptation to 

 various temperature conditions. 



In General. — It is possible that more detailed measurements, taken 

 perhaps on a different basis than that used by climatologists, would 

 secure more uniformity than the figures cited above. Temperatures 

 taken in sunlight would seem to be more reliable expressions of conditions 

 in buds and leaves than those taken in shade. Some writers have sug- 

 gested maximum temperatures as the basis for calculations. In any case, 

 however, it seems doubtful if temperature alone can be made the index 

 of plant activities. 



Schimper^"^ aptly points out that "different organs and functions require 

 very different amounts of heat, that unfavorable temperatures cause subsequent 

 inhibition, and that other factors besides heat, especially humidity, cooperate 

 and intervene. We need not, then, be surprised if there is very Uttle accord in 

 phaenological observations, and that the utmost one can do is to admit their 

 having a certain importance for purely descriptive geographical botany in the 

 characterization of certain districts. No importance, on the other hand, need 

 be assigned to the theoretical views, nor to the sum total of temperatures." 



OPTIMUM TEMPERATURES 



It is well known that some plants grow at lower temperatures than 

 others. The necessity of a certain amount of heat during the growing 

 season is recognized in the statement that in some regions the summers are 

 too cool for certain fruits. 



Variation within the Species or Variety.— In considerable areas of 

 north central Europe, peach growing is limited, not by the cold of winter 

 but by the low summer temperature. The same limitation, though 

 less obvious, probably applies to pears, as is indicated by the transition 

 from open exposures in the south of France to the trained and sheltered 

 trees in the north. Among plants of warmer climates the date palm 

 shows a heat requirement that is not satisfied in all sections where the 



