54 
COURSE OF THE SAP. 
[Part II. 
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 lower surfaces; 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. 
I have only had opportunity of seeing these 
theories of M. Bonnet quoted. According to 
this class of physiologists, of which the great 
chemist Liebig is the modern oracle, when trees 
are in full leaf they receive their entire nutri¬ 
ment through their leaves from the atmosphere, 
and “ the complete dryness of the soil ” would 
not then injure them. If this were so, if a 
branch were cut in full leaf, and suspended from 
those among which it grew, it should remain 
alive till the fall of the leaf; or when trees were 
cut down at Midsummer, till the fall of the leaf 
the heads would remain alive, and the roots 
would immediately die. The reverse of this is 
