248 FUNDAMENTALS OF FRUIT PRODUCTION 



observations in sections where these fruits flourish; the growing season 

 temperatures thus indicated range from 54°F. for the gooseberry, 59°F. 

 for the apple, and 65°F. for the peach to 85°F. for the mango. Goff^'' 

 found that root growth begins very early in most fruit plants in Wisconsin, 

 starting in most cases in advance of the buds. When currant buds were 

 but little swollen some of the new roots were 3 inches long. Goff stated, 

 however, that warmer temperatures did not accelerate root growth as 

 much as might be expected from the early start. Comparison of the 

 growth of young apple trees under various systems of culture, with accom- 

 panying differences in soil temperature, has shown that the two systems 

 inducing the greatest extremes in temperature resulted in practically 

 the same growth. ^^^ xhe extremes, however, were not widely separated. 

 It would seem that in some cases when a choice of stocks is possible 

 the adaptability of the several stocks to soil temperatures should be 

 considered, along with other factors. It appears rather illogical, for 

 example, to plant prune trees on peach roots in a soil so cold that it 

 would not be considered suitable for peaches. An instance of at least 

 partial adaptability to soil temperatures has been reported in Baluchistan, 

 where plums, peaches, etc., on Black Damask and Mazzard roots repeat- 

 edly failed to thrive, though the same combinations are satisfactory 

 in Great Britain. ^^ Using other stocks such as Mariana, Myrobolan 

 and Mahaleb, that apparently are better adapted to hot, dry soils, much 

 better results were secured. 



INDIRECT TEMPERATURE EFFECTS 



Finally, another limiting effect of growing season temperatures should 

 be considered, namely, that on fungous diseases. Apple scab, for example, 

 has a generally northern range, suggesting adaptability to cool summers, 

 while blotch is confined to sections with rather warm summers. Pear 

 blight is distinctly a warm weather disease; brown rot is favored by 

 high temperatures in conjunction with humidity. All these diseases take 

 toll of the fruit grown where they are present; brown rot, in conjunction 

 with curculio, makes plum growing a hazardous occupation in the south- 

 east United States and blight practically prohibits the commercial 

 production of the European pear in the southeast and in the Mississippi 

 valley. 



Summary. — Functional activity and growth of any kind in a plant 

 have definite temperature requirements. Within the limits between 

 which the growth processes can proceed development is slowest near each 

 extreme — that is, close to the lower and close to the upper hmit. Growth 

 is most rapid at an optimum temperature somewhere between the two 

 extremes, but usually nearer the upper than the lower limit. Further- 

 more the optimum for certain growth processes is quite different from 

 that for others within the same plant and the extremes hkewise may 



