124 INCREASE OF HEAT. 



diately after the conclusion of the work a heavy 

 shower fell, and on the next day the difference was 

 very marked in their relative dryness. The land 

 was all planted with the same crop, and the returns 

 from those sections which were aerated was esti- 

 mated to be one-half more. 



Prof. Stockhardt, in his "Agricultural Chemistry," 

 as translated by Dr. Henfry, thus enumerates the 

 effects of drainage: 



" Wet soils become drier. All our cultivated 

 plants are land plants, and these require for vig- 

 orous growth a soil which has moisture, but not in 

 that liquid form which it presents in standing water. 

 When the latter is the case, the roots can only 

 penetrate the earth to the depth at which the water 

 stands, and aquatic plants are likely to make their 

 appearance and displace those of land growth. 



" Some peaty soil becomes too mellow, because air 

 enters it, where the water had previously been, and 

 makes the humus produced by putrefaction decay 

 in too soft a state. 



" Cold soil becomes ivarmei\ for it now retains the 

 heat of the sun and air, which previously was in 

 great measure expended in producing evaporation. 



" Heavy soil becomes looser, more easihj crumbled, 

 and softer ; when it dries, finer cracks are formed 

 iLan in the undrained, tenacious soils, and it is 

 more readily worked. 



*' Sluggish soil becomes more active and powerful; 



