140 THE CULTURE OF FARM CROPS. 



with the character of the land. It has been found that the 

 surface of the earth acquires a much higher temperature 

 when the rays of the sun beat down upon it, than the sur- 

 rounding air. A temperature of 110 or 120 degrees is quite 

 commonly acquired; while at times it rises to 150 ; while the 

 air is no warmer than 70 or 80 degrees in the shade. Thus 

 the soil is provided with a supply of heat which is of the 

 greatest importance to the growing crops: especially to 

 those subtropical plants, such as corn, which delight in this 

 genial warmth. Every farmer knows how his corn shoots 

 up in its growth on those warm moist nights, following hot 

 days, when the accumulated heat of the soil is retained, and 

 intensifies those chemical agencies which change the plant 

 food in the soil into vegetable tissue and thus force the sur- 

 prising growth which is noticed under such favorable cir- 

 cumstances. A corn plant has been known to increase in 

 height nearly 2 inches in the 8 hours between the light of 

 two days in August, at a season when the growth is most 

 luxuriant. 



This power of absorbing heat depends upon the color as 

 well as the texture of the soil. Every one knows how the 

 suns heat is absorbed by dark colored clothes, and that it*is 

 for this reason that light colored clothing is worn in the 

 summer ; also how a black kettle w T ill heat water over a fire 

 more quickly than a bright one. In the same way and for 

 the same reason a dark colored soil absorbs very much more 

 heat than a light colored one, and hence the vegetation upon 

 dark soils will be more luxuriant than upon light ones. 

 The black prairie soils of the Western States produce more 

 and better corn for this reason than the white or grey soils 

 of other localities, and when light sandy soils are darkened 

 in color by a liberal admixture of peat compost, they are 

 improved very considerably. 



This power of absorbing heat possessed by dark colored 

 soils, however, is not accompanied by a corresponding te- 

 nacity or power of retaining heat ; for black peaty soils will 

 cool as much in one hour after night fall as a light sandy 

 or clay soil will in three. This difference however does not 



