cii. ri. 



COUKSE OF THE SAP. 



59 



as permanently to lay bare the wood, and to intercept 



the return of the sap through the bark, as long as the 



branch lives it will continue to increase in girthing 



above the ring, but not below it ; and when such a 



branch is sawed in two, lengthwise, each additional 



annual layer may be counted above the ring, but none 



below it. But if the growth in girthing were deposited 



from the upward sap, the parts of a branch below the 



ring would be more favourably situated for it than the 



parts above the ring ; also, if notches are made up a 



stem, the new growth comes first on the highest, and 



descends in succession. From these facts it is believed and sup- 

 posed to be 



that, after the sap has been elaborated in the leaf, in its deposited 



^ -L from the 



descent through the bark it deposits the new growth 

 in girthing. If, however, the sap is elaborated solely 

 in the leaf, and if the growth in girthing is deposited 

 solely from the descending sap in the bark, the growth 

 in girthing of the plum-stock of a grafted peach-tree 

 should be peach ; but the stock remains still plum, its 

 roots plum, its shoots plum, and its suckers plum. On 

 the other hand, if the elaboration were wholly in the 

 root or stem, and the new grov/th in girthing from the 

 upward sap, the wood and leaves of the peach would 

 become plum. But purple beech* and variegated 

 sycamore grow for ever unchanged, though engrafted 

 on common stocks, as a single branch of a plant 

 accidentally variegated will for ever retain its character. 

 When peach-scions are grafted or budded on 



* Purple beeclies may be raised from seed. I have one which 

 I planted ont in 1837, and have them of all ages since that. 



