CHAP. II. 



OF THE CHANGES INDUCED ON THE AIR 

 BY THE VEGETATION OF PLANTS. 



23. IN the former chapter it was shewn, 

 that water was a first and essential requisite to the 

 germination of the seed, and numerous facts prove 

 it to be equally necessary to the future progress of 

 the plant ; for if completely deprived of water, the 

 plant withers and dies, although every other requi- 

 site be present ; nor does it afterwards revive, even 

 although water be supplied. The quantity of this 

 necessary fluid that is daily absorbed by plants, va- 

 ries greatly according to their structure and habits, 

 to the temperature of the season, the supply of wa- 

 ter, and the state in which vegetation is going on. 

 After its absorption, it is again given out in great 

 part by transpiration ; and the degree in which this 

 latter process proceeds, must depend on the quan- 

 tity previously absorbed : and conversely, whatever 

 restrains the freedom of transpiration, must abridge 



