206 a “ HOW CROPS FEED. 
completely dry, or they had been fora long time acted 
upon by a powerful sun. Since, however, the sail was 
moist, the wilting could only arise from the inability of 
the roots to absorb water as rapidly as it exhaled from 
the leaves, owing to the low temperature. Further ex- 
periments showed that warming the soil in which the 
wilted plants stood, restored the foliage to its proper tur- 
gidity in a short time, and by surrounding the soil of a 
fresh plant with snow, the leaves wilted in three or four ; 
hours. 
Cabbages, winter colza, and beans, similarly circum- 
stanced, did not wilt, showing that different plants are un- 
equally affected. The general rule nevertheless appears to 
be established that within certain limits the root absorbs 
more vigorously at high than at low temperatures. 
_ The Amount of Loss of Water of Vegetation in Wilt- 
ing has been determined by Hesse (Vs. St., I, 248) in 
case of sugar-beet leaves. Of two similar leaves, one, 
gathered at evening after several days of dryness and sun- 
shine, contained 85, 74°|, of water; the other, gathered 
the next morning, two hours after arain storm, yielded 
89.57°|,. The difference was accordingly 3.8°|,. Other 
observations corroborated this result. 
Is Exhalation Indispensable to Plants ?—It was for 
along time supposed that transpiration is indispensable 
to the life of plants. It was taught that the water which 
the plant imbibes from the soil to replace that lost by ex- 
halation, is the means of bringing into its roots the min- 
eral and other soluble substances that serve for its nutri- 
ment. 
There are, however, strong grounds for believing that 
the current of water which ascends through a plant moves 
independently of the matters that may be in solution, 
either without or within it; and, moreover, the motion of 
soluble matters from the soil into the plant may go on, 
