222 APPLICATION OF PBINOIPLES. 



though the cellular horizontal system, through which 

 union by the first intention takes place, may be alive 

 on all parts of the section of a branch, yet that it is in 

 the bark, and in the space between the bark and 

 wood, that its developement is most rapid, and its 

 tendency to growth most easily excited and main- 

 tained. 



It is not, however, to be supposed that these opera- 

 tions can be performed indifferently, between any two 

 species, although such was formerly so general a 

 belief that it was asserted that roses became black 

 when grafted on Black Currants, and oranges crim- 

 son if worked on the Pomegranate* In point of 

 fact, the operations are successful in those cases only 

 where the stock and scion are very nearly allied ; and 

 the degree of success is in proportion to the degree of 

 affinity. Thus, varieties of the same species unite the 

 most freely, then species of the same genus, then 

 genera of the same natural order ; beyond which the 

 power does not extend, unless, in the case of parasites 

 like the Mistletoe, which grow indifferently upon 

 totally different plants. For instance, Pears work 

 freely upon Pears, very well on Quinces, less willing- 

 ly on Apples or Thorns, and not at all upon Plums 

 or Cherries ; while the Lilac will take on the Ash, 

 and the Olive on the Phillyrea, because they are 

 plants of the same natural order. M. Be Candolle 



* Et steriles platani malos gessgre, valentes 

 Castanese fagos, ornusque incamiit albo 

 Flore py ri, glandemque sues freg&re sub ulmis. 



Qeorg. lib. ii 



