CONTENTS. 



Vll 



PAGE 



First otlice of the leaf, transpiration and excretion . . . .44 



Leaf supposed by some to absorb the food of plants . . .45 

 Errors of Liebig .......... 46 



Second office of the leaf, the formation of winter-bud . . .58 

 Third office of the leaf, the changing of the sap from the upward 



conduit, the wood, to the downward conduit, the bark . . 58 

 The growth in girthing is from the downward sap, or dependent on 



it ; proof by experiment 58 



And supposed to be deposited from the bark . . . . .59 



But elaboration certainly takes place before the sap reaches the leaf 61 

 And also after it quits the leaf ....... 61 



Received theories of growth in girthing . . . . .61 



The pith or medulla, and medullary rays or silver grain . . .62 

 Medullary rays longitudinal plates, only bounded in length by the 



height of trees and length of branches and roots , . . .63 



The shake, and cup-shake 64 



Lateral as well as longitudinal flow of sap through the whole wood 65 

 The longitudinal pith-channels extend throughout the tree, from the 



pith of the original seedling to the finest ramifications of the roots 



and branches of the largest tree which is entirely alive . . 66 

 Diminution in the size of the pith and its disappearance vulgar errors 67 

 Whether the pith is the conduit of the upward sap or not . , 68 

 Do the central piths of budded buds, of grafts, and of the shoots of 



coppice-wood, communicate with Dutrochet's concentrical piths ? . 69 

 Office of the pith unknown ........ 72 



As the sap-channels are general, not peculiar, pruning increases the 



supply to the leader ......... 72 



A new layer of bark is formed every year . . . . .73 



That roots have no piths an error 76 



There is no true circulation of the sap like that of the blood of 



animals 78 



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 ......... 80 



The upward growth of a tree, or lengthening of its shoot, is by the 

 enlargement of all the parts of that shoot j and all these parts 

 progress bodily upward 80 



