218 PROPAGATION BY GRAFTING. 



of the one, should meet and join with the bark and wood of the 

 other. If the operation succeeds, the stock and the graft become 

 so completely united together, as to form in time but one tree, in 

 \vhich all mark of the original separation has disappeared. The 

 stock draws up from the soil the fluid, which the leaves of the 

 graft require ; these obtain carbon from the air, and elaborate 

 the crude sap into proper juice, a portion of which is supplied by 

 the graft to the stock for the extension of its own tissues, just 

 as if the stem really belonged to it. 



349. To effect this object, it is generally necessary to choose 

 as the stock, a plant either of the same species with the graft, or 

 one very closely allied to it ; and the less the relationship, the 

 more care and precaution must be taken to secure a union, by 

 bringing the newest layers of bark and wood into contact. It is 

 customary to select for the purpose, some less valuable form of 

 the same species ; thus the cultivated varieties of Pears and 

 Apples are grafted upon the Wild Pear and Crab. Or a species 

 nearly allied will sometimes answer almost as well, and, from 

 being readily procured, is commonly employed ; thus, Peaches 

 and Apricots are grafted on the common Plum. The operation 

 does not always succeed, between two species of different genera; 

 and it fails entirely, if an attempt is made to unite individuals 

 of different families. Thus, for example, Pears answer well 

 upon Pears, nearly as well upon Quinces, less freely upon Apples 

 or Thorns, and not at all upon Plums or Cherries, which are of 

 a different family. The Lilac will take upon the Ash, notwith- 

 standing their great apparent difference, because they are of the 

 same natural family ; but the Olive, which also belongs to the 

 same family, cannot be profitably grafted upon the Ash, since 

 the vegetation of these is too different, to allow them to live 

 long together. 



350. From what has been said regarding the readiness of the 

 Misseltoe (which may be considered as a natural graft), to grow 

 upon various kinds of trees, and the great similarity of the 

 ascending sap in most of these, it is evident that the cause, 

 which thus restrains the gardener in the choice of his stock, 

 is not merely the difference in the properties of the fluids of the 



