THE FKEE WATEll OF THE SOIL. 205 



vessel containini^ the plant and solution was closed above, 

 around the stem of the jilant, by glass plates and cement, 

 so that no loss of Mater could occux* except through the 

 l^lant itself, and tliis loss Avas ascertained by daily weigh- 

 ings. The result was that all the solutions mentioned, 

 excejit that of free nitric acid, quite imiformly retarded 

 transpiration to a degree varying from 10 to 90 i)er cent, 

 "Nvhile the free acid accelerated the transpiration in a cor- 

 responding manner, 



Sachs experimented also with four tobacco plnnts, two 

 situated in coarse sand and two in yellow loam. The 

 plants stood side by side exposed to the same temperature, 

 etc., and daily weigliings were made during a week or 

 more, to learn tlie amount of exI)alation. The result was 

 that the total loss, as Avell as the daily loss in the majority 

 of weighings, was greater from the plant growing in loam, 

 altliough through certain short 2>eriods the opposite was 

 noticed. 



f. Il^e 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 Aveighings up- 

 on tAvo tobacco plants of equal size, potted in portions of 

 the same soil and liaving their foliage exposed to the same 

 atmosphere. After observing their relative transpiration 

 when their roots Avere at the same temperature, one pot 

 Avas Avarmed a number of degrees, and the result Avas in- 

 variably observed that elevating the temjserature 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 43° F. A number of healthy tobacco and squash 

 plants, rooted in a soil kept nearly saturated Avith Avater, 

 were gioAving 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 Avere so wilted 

 that they hung doAvn like Avet cloths, as if the soil Avere 



