56 
COURSE OF THE SAP. 
[Part II. 
give off water, from all parts which are exposed 
to drought. 
Liebig tells us that “ leaves, twigs, and 
branches, when completely matured, as they do 
not become larger, do not need food for their 
support.” Why, then, do they droop when the 
supply is cut off, and revive when the roots only 
are watered ? Let any physiologist of this 
school apply this reasoning to his own “ com¬ 
pletely matured ” body, and cease to supply it 
with food because it has ceased to become larger. 
But if leaves 11 do not become larger,” the plants 
which bear them do. The formation of the 
bud, the downward growth, the growth in girth¬ 
ing, and the growth in elongation of the roots, 
are in full tide when the leaves have ceased “ to 
become larger;” and the leaves are doubtless 
essential to this increase. Suppose a gardener 
were to take Liebig’s word, and to refuse to 
water his pot greenhouse plants when turned 
out for the summer. Not one would survive. 
And why do they require watering when plants 
in the open ground do not ? Because the earth 
in the pots is exposed all round to drought from 
sun and air, while the upper surface only of the 
ground is exposed. If pot-plants are not 
watered, even in our moist English summer, 
