Bi EFFECTS OF FOREBTS ON HUMIDITY. 



fact that under trees or plants the moisture spreads for several 

 inches, eighteen or twenty it may be, over and through the banks 

 towards the tree, while at exposed places between the trees the 

 moisture spreads not above one or two inches from the surface 

 of the water. Btit this, so far from proving what was alleged, 

 may be adduced as evidence of the correctness of ray view of the 

 matter. The avatar spreads from the stream by what is called 

 capillary attraction, and spreads in all probability quite as far in the 

 exposed as in the covered spots, but where it is exposed it is con- 

 tinuously evaporated by the heat of the sun's rays, so that, excepting 

 during the night and early in the morning it never becomes visible in 

 the darkened hue of the soil, while under the shade of the trees it 

 has been protected from evaporation. There the water which has 

 spread so far is retained with very little loss. But at the exposed 

 parts of the bank there is a constant drain throughout the day. 

 Water evaporates ; more rises to supply its place ; but this is carried 

 off in like manner, till the setting of the sun suspends for a time this 

 wasteful process. So far from the tree stealing the water, it takes up 

 no more than it retains in the structure of its sap, wood, flowers, 

 fruit, and green leaves ; the heat is the thief, if thieving there be. 

 The tree has not stolen away the water which occasions the moisture 

 seen under its shade. The soil did that, and it did the same all 

 along the water-course ; and the tree, like the faithful dog. has 

 watched over and protected that portion from the heat of the direct 

 rays of the sun, by which it would otherwise have been conveyed away 

 and transported by the air to regions, it may be, far remote." 



While I adhere to the statement thus made, I may add that in 

 the remark which called it forth there is — as there often is in popular 

 remarks — a mixture of truth and error ; it was neither absolutely 

 correct nor absolutely erroneous : the tree had actually withdrawn 

 moisture from the streamlet, for thence it was that the moisture re- 

 tained in its structure and the moisture evaporated by its leaves had 

 mainly been obtained ; but the blackness and dampness of the soil 

 between the streamlet and the tree to which it was that my attention 

 was called had not tlius been produced, — that moisture had not been 

 occasioned by the vegetation of the tree but by the capillary attrac- 

 tion of the soil. Tl>e shade of the tree had prevented the direct rays 

 of the Bun falling upon this as they did upon the ground around • 

 thus an evaporation, such as had dried the ground beyond, had been 

 prevented ; and in the same way is the desiccation of a road retarded 

 where it is overshadowed by trees. 



