THE CLIMATE OF WESTERN CANADA 25 



Table IV. — Temperature Necessary for Oermination and Growth* 



Crop Germination Growth 



Min. Opt. Max. Min. Opt, Max. 



Wheat 41 84, 108 32-40 77-88 88-98 



Barley 41 84 99 



Beans 49 93 115 Peas 



Corn 49 93 115 40-51 88-98 98-111 



Pumpkins 52 93 115 61-60 98-111 111-122 



Melons 60-65 88-98 



It will be observed that the grain crops and peas 

 will germinate and grow at relatively low temper- 

 atures, while corn demands more heat and truck crops, 

 like melons, still higher temperatures both for germina- 

 tion and for growth. 



15. The Measure of the Heat Supply. — The chief source 

 of heat is the sun, although the stars and the interior of 

 the earth also slightly increase the surface temperatures. 

 The sun's heat reaches the earth by direct radiation, by 

 radiation and conduction from the atmosphere, and by 

 warm rains. The soil temperature is affected also by the 

 heat given off from decaying plant tissues. The meas- 

 ure of the heat supply is the temperature, and the 

 temperature data that chiefly concern the farmer are, 

 (1) the average and extreme dates of the last spring 

 and first fall frosts, (2) the average temperature of the 

 growing season, (3) the extremes of temperature in the 

 growing season, and (4) the total amount of heat re- 

 ceived during the growing season. The time and 

 severity of the last spring and first fall frosts fix the 

 length of the growing season for cereals and together 

 ■ with the average temperature of the frost-free season 

 determine, approximately at least, the total units of 



As quoted by Lyon, Fippin & Buckman in "Soils, their Proper- 

 ties and Management." 



