Chap. II.] 
COURSE OF THE SAP. 
67 
that the “ immeasurably luxuriant vegetation ” 
is drawn by the roots from the soil, not by the 
leaves from the exotic carbonic acid imported 
on so grand a scale by Liebig from the north 
and south? 
Then, the oxygen evolved by plants is essential 
to the breathing of man and animals. And 
“ thus, cultivation heightens the healthy state of 
a country,” and a previously healthy “ country 
would be rendered quite uninhabitable by the 
cessation of all cultivation.” It appears here 
that we poor beasts grow our air from our 
plants, as well as our plants from our air. But 
has Nature no plants without cultivation? And 
in countries where she has no plants, as on sandy 
deserts, or in regions of eternal snow, is the air 
impure and unwholesome ? Or does more ma¬ 
laria hang over the wide wide sea than over tro¬ 
pical swamps, which are “the proper, constant, 
and inexhaustible sources of oxygen gas”? 
In deciduous trees, and in the greater part of 
English evergreens, if each leaf does not form a 
bud, at least each leaf is accompanied by a bud. 
And I imagine that one essential office of the 
leaf is the formation and summer nutriment of 
the ivinter- bud. Each bud forms a shoot, or a 
flower, or both, the next year. This is the 
Second office of 
leaves, forma¬ 
tion of the 
winter-bud. 
