viii 



CONTENTS. 



PAGE 



The downward growth of the tree, or lengthening of the root, is 



simply by growth at the end of the root . . . . .81 

 By what agency is the head directed upward and the root down- 

 ward ? 81 



Turgescence, and the action of light on turgescence, probably direct 



the growth of the head of the plant , . . . . . 83 

 Cellular formation of the bark of green shoots ..... 83 

 How turgescence acts on the cellular formation . . . .83 

 How light acts on this turgescence 84 



Dutrochet, Knight, Davy^ &c., think that gravity directs the growth 



both of the head and roots of trees. Experiments in proof . . 85 

 Upward growth of lirst gemniule when deprived of light . . 88 

 Crane-neck growth of first gemmule of a double-seeded plant, to 



shield it while forced through the earth . . . . .89 

 Roots grow through the earth almost without force . . . .89 

 Provision to enable the gemmule of a single-seeded plant to thrust 



itself through the earth ........ 91 



Probable distinct organisation of the first gemmule . . .92 

 Strong downward determination of tap-root, and probable distinct 



organisation of it . . . . . . . . . .94 



Tap-root only proper to seedlings, and a contrivance for fixing them 97 

 That the growth of the head and root of a tree is directed by 



gravity disputed 101 



General growth of head towards light ; general growth of root to 



wherever it can find good soil . . . . . . . lOo 



CHAPTER IV. 



MISCELLANEOUS. 



Barked horse-chestnut at Esher ....... 108 



Best time for transplanting with the ball of earth . . . . ] 13 



Absurd notion that trees deradicate as well as defoliate . . .116 

 The growth in girthing descending from the head or any particular 

 branch is general round the stem ; but it is greater on the side 



proper to the branch . , . ' 118 



And the growth may be mecJianicaUy and continually turned from 

 one side of the stem to the other . . . . . . ,119 



Lateral upicard. growth of the root . . , . . . .119 



Origin of spurs and the swell of the roots 122 



A tap-rooted tree should have no spurs or swell of the root . . ] 24 

 Girthing of the stem dependent on the quantity of branches above it 125 

 There is a constant circulation of sap even in winter . . . 126 



