300 PRINCIPLES OF BOTANY, ETC. 
lowing manner: The root takes up moisture and a 
small quantity of gas from the ground, and carries 
them, properly digested, to the stem. ‘This, as long 
as green, mhales air and particles dissolved in it, and 
variously prepares it in its vessels. - The leaves im- 
bibe air and moisture, and again transpire gaseous 
fluids and moisture, and carry what. they have pre- 
pared from those principles to the young bud, or 
the evolving part of the plant, as its food. That 
buds are nourished by means of the leaves needs 
no further proof than that in tender twigs, if we 
take off the leaves at the time when they ought to 
nourish the buds, these last cease to grow and to 
unfold themselves. If the leaves are taken off from 
branches which are already ligneous, they may be 
restored by the accumulated quantity of at in the 
cellular texture. 
The sap of plants we know, (§ 237), has some 
likeness to the blood of animals. Plants collect a 
great quantity of it, to be provided against all pos- 
sible accidents. Bulbs take up much sap, and with 
it form, at the time of flowering, all necessary parts. 
Du Hamel with Grew calls the sap of plants cambium. 
He could perceive no connexion betwixt the wood 
and the bark of a willow-tree, but found there a 
fluid, which became in the open air gelatinous and 
tenacious. He deprived a cherry-tree the whole 
length of its stem of the bark, when it was in full 
blossom, and covered it with a thick layer of straw ; 
the tree bore no fruit, lost many of its leaves, and 
even some boughs. ‘The next year it had not yet 
recovered, but in the third a new bark was formed 
from 
