EFFECTS OF TRANSP1KATION. 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 by the diminished evaporation under the branches. Hence 

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

 is released slowlv by drainage. But if the trees are so scattered 



IS 



as not materially to reduce evaporation from the ground, the 

 effect of transpiration in diminishing the moisture of the soil is 

 readily shown. It is noted especially 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 

 successfully employed in the drainage of marshy soil by transpi- 

 ration probably the species of Eucalyptus J (notably E. globulus) 

 are most efficient. 



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

 that leaves which wilt during the daytime from slight dryness 

 of the soil may recover their turgescence during the night, for 

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

 water is very slight, so that there is a speedy readjustment of 

 the equilibrium which \vas disturbed during the day. It is stiil 

 a disputed point whether wilted leaves can absorb any appre- 

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

 Experiments by Duchartre- indicate that the amount must be 

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

 from the plant can absorb water through the leaves is well 

 known, and has been already alluded to. 



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

 Also an article by H. X. Draper in Chambers's Journal, Iviii. 193, reprinted 

 in Littell's Living Age, cxlix. 376. 



2 Ann. des Sc. nat. , ser. 4, tome xv., 1861, p. 109. 



