46 



COURSE OF THE SAP. 



PT. ir. 



some to leaf is to absorb moisture. M. Bonnet tells us that the 



absorb the 



plants! ^^^^ formed to absorb, chiefly from the lower part, 

 because dew ascends. But as dew is a condensation of 

 moisture which is suspended in the atmosphere, it can- 

 not be said to ascend more than to descend ; and the 

 physiologist forgets that rain descends. But I do not 

 think that M. Bonnet's facts are more to be depended 

 on than his reasoning. He states that if leaves are 

 floated on water on their upper surfaces, they will die 

 as soon as if they were not put in water, but if they are 

 floated on their lower surfaces they will remain alive 

 as long as if their stalks were immersed in water. I 

 tried this experiment in 1836, and found that the 

 leaves floated on their upper surfaces remained alive as 

 long, or rather longer, than those on their low^er sur- 

 faces ; one remained in part alive for six weeks. But 

 the fact that detached leaves or branches placed on 

 water, but with the ends of their stalks out, will remain 

 alive much longer than if suspended in the air, proves 

 lateral absorption. And on this assumption the wetted 

 hay-band is placed round the stem of trees packed for 

 long journeys. 



Errors of I havc ouly had opportunity of seeing these theories 



Liebig. 



of M. Bonnet quoted. According to this class of phy- 

 siologists, of which the great chemist Liebig is the 

 modern oracle, when trees are in full leaf they receive 

 their entire nutriment through their leaves from the 

 atmosphere, and ' the complete dryness of the soil ' 

 would not then injure them. If this were so, if a 



