28 



PROPAGATION OF VARIETIES. 



branch, maintains its individuality by preparing its own proper nourish- 

 ment, or organizing matter, out of that general aliment the sap. In- 

 deed, according to De Candolle,* each separate cellule of the inner bark 

 has this power of preparing its food according to its nature ; in proof of 

 which a striking experiment has been tried by grafting rings of bark, of 

 different allied species, one above another, on the same tree, without 

 allowing any buds to grow upon them. On cutting down and examining 

 this tree, it was found that under each ring of bark was deposited the 

 proper wood of its species, thus clearly proving the power of the bark in 

 preserving its identity, even without leaves. 



On the other hand, though the stock increases in size by the woody 

 matter received in the descending sap from the graft, yet as this descends 

 through the inner bark of the stock, it is elaborated by, and receives its 

 character from the latter ; so that, after a tree has been grafted fifty 

 years, a shoot which springs out from its trunk below the place of union 

 will always be found to bear the original wild fruit, and not to have been 

 in the least affected by the graft. 



But whilst grafting never effects any alteration in the identity of the 

 variety or species of fruit, still it is not to be denied that the stock does 

 exert certain influences over the habits of the graft. The most important 

 of these are dwarfing, inducing fruitfulness, and adapting the graft to the 

 soil or climate. 



Thus every one knows that the slower habit of growth in the Quince 

 stock is shared by the Pear grafted upon it, which becomes a dwarf ; as 

 does also the Apple when worked on the Paradise stock, and, in some 

 degree, the Peach on the Plum. The want of entire similarity of struc- 

 ture between the stock and graft confines the growth of the latter, 

 and changes it, in the case of the Pear, from a lofty tree to a shrub of 

 eight or ten feet in height. The effect of this difference of structure is 

 very apparent, when the Peach is grafted on the Plum, in the greater 

 size of the trunk above, as compared with that below the graft ; a fact 

 which seems to arise from the obstruction which the descending sap of 

 the graft finds in its course through the bark of the stock. 



To account for the earlier and greater fruitfulness caused by grafting 

 on a stock of slower growth, Mr. Knight, in one of his able papers, offers 

 the following excellent remarks : — 



" The disposition in young trees to produce and nourish blossom buds 

 and fruit is increased by this apparent obstruction of the descending 

 sap ; and the fruit, I think, ripens somewhat earlier than upon other 

 young trees of the same age which grow upon stocks of their own species. 

 But the growth and vigor of the tree, and its power to nourish a succes- 

 sion of heavy crops, are diminished, apparently, by the stagnation in the 

 branches and stock of a portion of that sap which, in a tree growing on 

 its own stem or upon a stock of its own species, would descend to nourish 

 and promote the extension of its own roots. The practice, therefore, of 

 grafting the Pear on the Quince, and the Peach on the Plum, when ex- 

 tensive growth and durability are wanted, is wrong ; but it is eligible 

 wherever it is wished to diminish the vigor and growth of the tree, and 

 its durability is not so important." 



In adapting the graft to the soil the stock has a marked influence. 

 Thus in dry chalky soils, where the Peach on its own roots will scarcely 



Physiologie Vegetable. 



