CHAPTER III.
CHAPTER III.
UPWARD GROWTH OF THE HEAD, AND DOWNWARD GROWTH OF THE ROOTS.
Upward growth of the head, and downward growth of the roots, considered together
The upward growth of a tree, or lengthening of its shoot, is by the enlargement of all the parts of that shoot; and all these parts progress bodily upward . . . . , . ,
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The downward growth of the tree, or lengthening of the root, is simply by growth at the end of the root. .
By what agency is the head directed upward and the root down- ward P , ; ‘
Turgescence, and the action of light on turgescence, probably direct the growth of the head of the plant,
Cellular formation of the bark of green shoots.
How turgescence acts on the cellular formation
How light acts on this turgescence .
Dutrochet, Knight, Davy, &c., think that gravity directs the growth both of the head and roots of trees. Experiments in proof .
Upward growth of first gemmule when deprived of light
Crane-neck growth of first gemmule of a double-seeded plant, to shield it while forced through the earth
Roots grow through the earth almost without force .
Provision to enable the gemmule of a single-seaded plant to thr ust itself through the earth .
Probable distinct organisation of the first gemmule
Strong downward determination of tap-root, and probable distinct organisation of it.
Tap-root only proper to seedlings, and a contrivance for fixing them
That the growth of the head and root of a tree is directed by gravity disputed .
General growth of head: towards light ; ‘general growth of root to wherever it can find good soil , . ;