PLANT PROPAGATION 113 



Decaying organic matter furnishes some heat to the soil. For 

 example, manure heats the soil to a limited extent when it is spread 

 on the surface and plowed in. ... The sun is by far the most 

 important source of heat for the soil. When its rays are nearly 

 vertical there is tropical heat ; when its rays are withheld, the land 

 is locked in snow and ice. The heat received at the surface passes 

 downward by conduction." l 



125. Cultivation of the soil. A moment's thought will 

 convince us that since all the food of man is ultimately de- 

 rived from plants, any measures that tend to improve crops 

 and reduce the cost of crop 

 production are of vital in- 

 terest to all of us. In the 

 past, before much was 

 known in regard to scien- 

 tific principles, farmers 

 put their seeds in the 

 ground, cultivated them 



relatively little, and trusted Nature to do the rest. In 

 recent times, however, man has learned a great deal in 

 regard to soils, crops, and methods of cultivation, so that 

 the modern farmer is often able to double the yield of a 

 given area. The investigations of the National and State 

 Departments of Agriculture have done much to make farm- 

 ing a science, and the future will doubtless see far greater 

 improvements. 



For the cultivation of plants the first requisite is a suitable 

 preparation of the soil. This involves, in the first place, 

 plowing, which turns under any weeds or other plants that 

 may have grown there before and which prepares for the work 

 of the harrow, an implement which pulverizes the soil so that 



1 Bailey's "Cyclopedia of American Agriculture," Vol. I, "Farms," 

 pp. 355, 356. 



