The free water of the soil. 199 



perfection when trained against the sunny side of a «all. 

 It is tlius that in the nortli of England pears and pkims 

 are raised in the most unfavorable seasons, and that the 

 vineyards of Fontainehleau produce such delicious Chas- 

 selas grapes fur the Paris market, the vines being trained 

 against walls on the Tliomery system. 



In the Rhine district grape vines are kept low and as 

 near the soil as possible, so that the heat of the sun may be 

 reflected back upon them from the ground, and the ripen- 

 ing is then carried through the nights by the heat radiated 

 from the earth. — {Journal Highland and Agricidtural 

 Society, July, I808, p. 347.) 



Vegetation. — Malaguti and Durocher also studied the 

 effect of a sod on the temperature of the soil. They ob- 

 served that it hindered the warming of the soil, and in- 

 deed to about the same extent as a layer of earth of three 

 inches depth. Thus a thermometer four inches deep in 

 green-sward acquires the same temperature as one seven 

 inches deep in the same soil not grassed. 



CHAPTER V. 



THE SOIL AS A SOURCE OF FOOD TO CROPS.— 



INGREDIENTS WHOSE ELEMENTS ARE OF 



ATMOSPHERIC ORIGIN. 

 I 



§ 1. 



THE FREE WATER OF THE SOIL IN ITS RELATIONS TO 

 VEGETABLE NUTRITION. 



Water may exist free in the soil in three conditions, 

 which we designate i-cspectively hydrostatic, capillary, 

 and hygroscopic. 



Hydrostatic or Flowing* Water is water visible as 



I. e., capable of flowing. 



