THE FREE WATER OF THE SOIL. 199 
perfection when trained against the sunny side of a wall. 
It is thus that in the north of England pears and plums 
are raised in the most unfavorable seasons, and that the 
vineyards of Fontainebleau produce such delicious Chas- 
selas grapes for the Paris market, the vines being trained 
against walls on the Thomery 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 Agricultural 
Society, July, 1858, 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. 
§ 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 respectively hydrostatic, capillary, 
and hygroscopic. , 
Hydrostatic or Flowing * Water is water visible as 
* I. e., capable of flowing. 
2 
