CHAPTER III. 



Disputed ajtd Secoxbaet Phexomzsa of Yvibeiatios. 



Bhsides the phenomena of vegetation which have been detailed 

 there are other allied phenomena, the import of which is more open 

 to question : amongst these may be reckoned the absorption of mois- 

 ture by the leaves of plants, the production of water by the plants 

 themselves, and the dropping of water fit)m the leaves of certain 

 trees. 



Sect. L — On the Absorption of Moisture by the Leaves of PlatUs. 



It is a prevalent opinion that moisture is absorbed by plants by 

 their leaves. I scarcely open a popular treatise on the subject in 

 which I do not meet with it ; but I have met with no evidence that 

 this is a normal action of leaves, excepting to a very limited and 

 easily defined extent. Abnormal action of leaves absorbing moisture 

 would prove as little as the abnormal absorption of moisture and 

 nutriment into the human firame by enemas and baths ; and the absorp- 

 tion of moisture by gigantic algae over the whole surface of their stalks 

 and their fronds proves as little. But this cannot be said of experi- 

 ments which have been made on the growth of epiphytes and of 

 mundane plants, which have grown and flourished when freed of all 

 soil; or of trees growing naturally and at the same time luxuriantly 

 on narrow ridges, on steep declivities, on partially decayed stumps 

 many feet above the ground, on waUs of high buildings, and on rocks, 

 in situations where the earth within reach of their roots could not 

 possibly, it is allied, contain the tenth part of the water which, 

 according to Sehleiden and Pfaff, they evaporate in a day. There 

 are, too, forests of great extent on high blofi^ and well-drained table- 

 lands wher^ it is said, " there can exist neither in the subsoil nor in 

 infiltration from neighbouring r^ons an adequate source of supply 

 for such consumption." 



These are &eta ratablished beyond all question ; but in r^aid to 

 what seems to be the natural condnsion, that in such cases the moia- 



