90 The Potato 



not all know that the direct effect of great heat is per- 

 haps even more harmful than the lack of water. The 

 results of unchecked attacks of insects like the Colorado 

 potato-beetle or of the late blight and rot> are other 

 familiar examples. The potato-grower who would raise 

 good yields every year through a series of years must 

 study very carefully every factor which enters into the 

 growing of potatoes . under his particular conditions, 

 with the idea of making sure that no one condition 

 will limit the results of his labor in other directions. 

 Such care counts heavily in increasing the income of the 

 farm, because seasons in which a crop is generally poor 

 from any cause are the ones in which prices are high. 



Heat 



Numerous experiments have shown that temperatures 

 in the soil above certain limits injure the vitality of the 

 potato plant. The extent of the injury depends on the 

 degree of heat and on other injurious factors, as drouth 

 and insect injury. The effect varies from reduction in 

 yield to practical failure with tubers ruined for use as 

 seed. Potatoes are not grown in the South in midsum- 

 mer. When grown in the months of late winter and spring, 

 the vitality of the tubers for use as seed is ruined by the 

 heat at the time the tubers mature. The "second-crop" 

 for seed in the South is planted in July or August and 

 forms its tubers in the cool weather of late fall. At this 

 time seed of good vitality is obtained. Near the Canadian 

 line and in the Rocky Mountain region there is little more 

 time in the whole growing season than is needed by the 

 late main-crop varieties. When hot seasons occiu* there, 

 as at Ottawa, Canada, in 1906-7-8. and at Greeley, Colo- 



