ATJIO.SPUKKIC AIU AS TIIK FOOD OF I LANTS. oO 



Water then exists in the atmosphere during the periods 

 of vegetable activity as gas or vapor,* and as liquid. In 

 the former state it is almost perpe'tually rising into the air, 

 while in the latter form it frequently falls again to the 

 ground. It is thus in a continual transition, back and 

 forth, from the earth to the sky, and from the sky to the 

 earth. 



We have given the average quantity of water-vapor in 

 the air at one per cent ; but the amount is very variable, 

 and is almost constantly fluctuating. It may range from 

 less than one-hnlf to two and a half or three per cent, ac- 

 cording to temperature and othei- circumstances. 



When the air is damp, it is saturated with moisture, so 

 that water is readily deposited upon cool objects. On the 

 other hand, when dry, it is capable of taking up additional 

 moisture, and thus ficilitates evaporation. 



Is Atmospheric Water Absorbed by Plants 1— It has 



long been supposed that growing vegetation has the power 

 to absorb vapor of water from the atmosphere by its 

 foliage, as well as to imbibe the liquid water which in the 

 form of rain and dew may come in contact with its leaves. 

 Experiments which have been instituted for the purpose 

 of ascertaining the exact state of this question have, how- 

 ever, demonstrated that agricultural plants gather little or 

 no water from these sources. 



The wilting of a plant results from the fact that the 

 leaves suffer water to evaporate from them more rapidly 

 than the roots can take it up. The speedy reviving of a 

 wilted plant on the falling of a sudden rain or on the depo- 

 sition of dew depends, not so much on the absorption by 

 the foliasie, of the water that gathers on it, as it does 



* While there is properly no essential dift'orence between a gas and a vapor, 

 the former term is commonly applied more especially to aeriform bodies which 

 are not readily brought to the liquid state, and the latter to those which are easily 

 condensed to liquids or solids. 



