Chap. II.] 
COURSE OF THE SAP. 
65 
gooseberries, raspberries, currants, &c. Straw¬ 
berries make their great growth after ripening 
their fruit. 
Deciduous trees defoliate at the end of au¬ 
tumn, though this is very much an affair of 
temperature; that is, the same tree, in different 
latitudes, will keep its leaves later directly as 
warmth, but it will ripen its fruit earlier directly 
as the warmth of the climate. Evergreens shed 
one year’s leaves at the end of winter. But 
neither of these defoliations has the slightest 
reference to the ripening of the fruit; and the 
time of ripening of the fruit has no reference to 
any general chemical causes, but to the par¬ 
ticular constitution of the plant. 
Liebig also makes plants play fast and loose 
in reference to their carbonic acid and oxygen. 
In the light, they absorb carbonic acid, and 
give off oxygen; vice versd, in the dark. All 
plants throughout the globe are, in point of 
time, for six months in the year in the light, and 
for six months in the dark. Therefore, all ever¬ 
green plants and pastures absorb and give off 
each gas for equal periods of time; not in equal 
volumes, however, according to Liebig. 
“ The proper, constant, and inexhaustible 
sources of oxygen gas are the tropics and warm 
F 
