THE FREE WATER OF THE SOIL. 205 
vessel containing the plant and solution was closed above, 
around the stem of the plant, by glass plates and cement, 
so that no loss of water could occur except through the 
plant itself, and this loss was ascertained by daily weigh- 
ings. The result was that all the solutions mentioned, 
except that of free nitric acid, quite uniformly retarded 
transpiration to a degree varying from 10 to 90 per cent, 
while the free acid accelerated the transpiration in a cor- 
responding manner. 
Sachs experimented also with four tobacco plants, two 
situated in coarse sand and two in yellow loam. The 
plants stood side by side exposed to the same temperature, 
etc., and daily weighings were made during a week or 
more, to learn the amount of exhalation. The result was 
that the total loss, as well as the daily loss in the majority 
of weighings, was greater from the plant growing in loam, 
although through certain short periods the opposite was 
noticed. 
J. The temperature of the soil considerably affects the 
rate of transpiration by influencing the amount of absorp- 
tion at the roots. Sachs made a number of weighings up- 
on two tobacco plants of equal size, potted in portions of 
the same soil and having their foliage exposed to the same 
atmosphere. After observing their relative transpiration 
when their roots were at the same temperature, one pot 
‘was warmed a number of degrees, and the result was in- 
variably observed that elevating the temperature of the 
soil increased the transpiration. 
The same observer subsequently noticed the entire sup- 
pression of absorption by a reduction of temperature tc 
41° to 48° F. A number of healthy tobacco and squash 
plants, rooted in a soil kept nearly saturated with water, 
were growing late in November in a room, the tempera- 
ture of which fell at night to the point just named. In 
the morning the leaves of these plants were so wilted 
that they hung down like wet cloths, as if the soil were 
