VEGETATIVE MULTIPLICATION. 617 



a shoot is caused to root high above ground, by surrounding one or more of 

 its nodes with a mass of earth kept moist by wet bandages or other 

 means. 



The artificial process of layering, practised commonly with Pinks, Ver- 

 benas, Aucuba, &c.,is analogous to the natural propagation of the Straw- 

 berry by runners. 



In all the cases comprehended in the above remarks, the adventitious 

 roots are formed most readily in the vicinity of buds, at the nodes, just 

 as we see them naturally occurring chiefly in those situations in creeping 

 plants, such as the Sand-Sedge (fig. 25), Mint, many Grasses, &c., which 

 root at every joint that comes into contact with moist soil, or in the 

 climbing Ivy, in which the adventitious roots forming its organs of attach- 

 ment to foreign bodies are produced in tufts a little below the leaves. 



Grafting. In the operations of budding and grafting, the parts of the 

 parent plant are caused to assume a kind of parasitical condition, in 

 which they stand in the same relation to a strange " stock " as they would 

 have held to their parent if left in their natural condition. The detached 

 bud or shoot is made to contract an organic union with the cambium- 

 region of a foreign stem, of which it becomes, as it were, a branch, deriving 

 its supplies of root-nourishment from it, and subsequently sending down in 

 return elaborated juices to contribute to the sustenance of its foster parent. 

 It is important to note, however, that in the case of distinct plants 

 thus combined they usually exercise no appreciable influence over each 

 other in regard to modifying the morphological characters of each ; the 

 connexion merely affects the scion and stock in the degree of activity of 

 the general physiological processes of nutrition, &c. Scions grafted on 

 stocks of more enduring character acquire greater vigour and fecundity ; 

 but the products of the buds of the scion, in the great majority of cases, 

 resemble in kind those of their parent, while the stock continues to grow 

 in its own way. The influence of the scion on the stock, is rendered 

 less noticeable in practice from the fact that buds or branches of the stock 

 are always removed after the scion has " taken," in order to concentrate 

 the sap in the latter; and if allowed to develop, the branches of the 

 stock formed below the scion mostly remain unaffected by the stranger 

 which has settled above them. 



Influence of Stock on Scion. A certain amount of physiological influence 

 of the stock over the scion is shown to exist by such facts of horticultural 

 experience as the dwarfing of certain varieties and their earlier or increased 

 productiveness according to the stock, as in the case of Apples on the Para- 

 dise stock, the fact that the fruit of the Pear is smaller and more highly 

 coloured when " worked on " the Quince or Medlar than when grafted on 

 Pear-stocks, and is earlier when worked on the Mountain Ash. It is not clear 

 here whether the alteration is attributable to greater or less vigour of the 

 stocks, or to an influence obstructing the return of elaborated sap towards 

 the roots, arising out of difference of texture of the wood. 



Influence of Scion on Stock. On the other hand, the scion has been in a 

 few cases observed to affect the stock. It is well known that the variety of 

 the Yellow Jasmine with variegated leaves, budded on a plant with 

 healthy green leaves, causes the gradual appearance of variegation through- 



