62 TREES ATTRACTORS OP HUMIDITY. 



elm iii full leaf affords a good example of this 

 supposed power ; but in the winter of the year, 

 when trees are perfectly denuded, this faculty of 

 creating moisture about them is equally obvious, 

 though not so profusely. A strongly marked 

 instance of this was witnessed by me, when ascend- 

 ing a hill in the month of March. The weather 

 had previously been very fine and dry, and the 

 road in a dusty state ; but a fog coming on, an ash 

 tree hanging over the road was dripping with 

 water so copiously, that the road beneath was in 

 a puddle, when the other parts continued dry, and 

 manifested no appearance of humidity. That 

 leaves imbibe moisture by one set of vessels and 

 discharge them by another is well known ; but 

 these imbibings are never discharged in falling 

 drops : the real mystery was, the fog in its progress 

 was impeded by the boughs of the tree, and gradu- 

 ally collected on the exposed side of them, until it 

 became drops of water, whereas the surrounding 

 country had only a mist flying over it. Thus in 

 fact the tree was no attractor, but a condenser ; the 

 gate of a field will in the same manner run down 

 with water on the one side, and be dry on the 

 other ; as will a stick, or a post, from the same 

 cause. It is upon this principle that currents of 

 air will be found under trees in summer, when little 

 is perceived in open places ; and the under leaves 

 and sprays will be curled and scorched at times, 



