EFFECTS OF TRANSPIRATION. 283 



755. Effect of transpiration upon the soil. The amount of 

 ■water taken from the soil by the trees of a forest and passed into 

 the air by transpiration is not as large as that accumulated in the 

 soil b}- tlie diminished evaporation under the branches. Hence 

 there is an accumulation of water in the shade of forests which 

 is released slowly )\y drainage. But if the trees are so scattered 

 as not materially to reduce evaporation fi'om the ground, the 

 effect of transpiration in diminishing the moisture of the soil is 

 ]-eadilj shown. It is noted especiall3- in case of large plants 

 having a great extent of exhaling surface, such, for instance, 

 as the common sunflower. Among the plants which have been 

 snccessfullj- emploj-ed in the drainage of marshj' soil by transpi- 

 ration probably the species of Eucalj-ptus '■ (notably E. globulus) 

 are most efficient. 



756. Do leaves absorb aqueous vapor 2 It is everywhere known 

 that leaves which wilt during the daytime from slight dryness 

 of the soil ma}- recover their turgescence during the night, for 

 then transpiration is reduced to a minimum, and the demand for 

 water is ver}' slight, so that there is a speedy readjustment of 

 the equilibrium which was disturbed during the day. It is still 

 a disputed point whether wilted leaves can absorb any appi'e- 

 ciable amount of water from the dew which falls upon them. 

 Experiments by Dnchartre ^ indicate that the amount must be 

 very small, if indeed auj- at all. That leafy branches detached 

 from the plant can absorb water through the leaves is well 

 known, and has been already alluded to. 



^ See a very interesting account by Mueller in Eucalyptographia, 1881. 

 Also an article by H. N. Draper in Chamljers's Journal, Iviii. 193, reprinted 

 in Littell's Living Age, cxlix. 376. 



2 Ann. (les Sc. uat, ser. 4, tome xv., 1861, p. 109. 



