Climate, Soils and Rotation 91 



rado, in 1911, there is no way of avoiding the heat by 

 early or late planting. In intermediate sections like those 

 from Long Island through to Iowa, growers avoid the 

 effects of summer heat to some extent by planting 

 either very early or very late. 



Another method used more or less unconsciously by 

 growers to prevent the effec ts of summer, is the use of 

 heat-resistant varieties. The ^IcCormick or Late Hoosier 

 is used in Vfrglhia and ^Maryland in summer because of 

 its peculiar ability to produce crops in weather too hot 

 for any other variety. The Rural or Blue-Sprout type 

 is the one which is grown more than any other in the 

 United States. It owes much of its popularity to the 

 fact that it will yield well in hot and dry seasons. The 

 use of the Green ^Mountain or ^^'^lite-Sprout type is 

 mainly confined to the cooler sections, like ]Maine, because 

 of its inability to stand heat as well as the Rural type. 

 The Triumph, Cobbler and Early Ohio types are used to 

 avoid extreme heat by growth in early spring rather than 

 by heat resistance. 



Heat is such a decisive factor in the growth of potatoes 

 in most of the L^nited States that growers must ever keep 

 its effects in mind if they are to succeed with the crop. 

 Many of these methods of culture now used have been 

 forced on growers unconsciously by the influence of heat 

 on the plant. ]\Iuch is to be expected in the future from 

 further investigations. Straw mulches have been found 

 very beneficial in the hot regions of the western plains to 

 insure coolness in the soil. It has been proved that 

 thorough spraying wkh bordeauxjuixture greatly reduces^ 

 the injury froln~heat. This is shown by some of the 

 gain from spraying in hot seasons when blight and insect 

 injury are absent. A possibility is in the use of over- 



