XX11 INTRODUCTION. 



new layers of wood instead of subterranean fibres. The 

 success of such practices, however, depends upon other 

 causes than those which influence the growth of cuttings. 

 It is necessary that an adhesion should take place 

 between the scion and the stock, so that when the 

 descending fibres of the buds shall have fixed themselves 

 upon the wood of the stock, they may not be liable to sub- 

 sequent separation. No one can have studied the economy 

 of the vegetable kingdom without having remarked that 

 there is a strong tendency to cohesion in bodies or parts 

 that are placed in contact with each other. Two stems 

 are tied together for some purpose : when the ligature 

 is removed, they are found to have grown into one : two 

 Cucumbers accidentally placed side by side, or two 

 Apples growing in contact with each other, form double 

 Cucumbers or double Apples ; and most of the normal 

 modifications of the leaves, floral envelopes, or fertilis- 

 ing organs, are due to various degrees of cohesion in 

 contiguous parts. This cohesion will be always found 

 to take place in the cellular tissue only, and never in the 

 vascular tissue. In the stems of all such trees as are 

 grafted by orchardists, the cellular tissue is found alive 

 only in the medullary rays and the liber ; it is therefore 

 essential, in the first place, that those parts, both in the 

 stock and the scion, should be placed in contact. In 

 regard to the medullary rays, these are so numerous and 

 so closely placed that it is scarcely possible that a portion 

 of one stem should be applied to another without the 

 medullary rays of both touching each other at many 

 points. No care, therefore, is required to ensure this, 

 which may be safely left to chance. But in regard to 

 the liber, as this is confined to a narrow strip in both 

 stock and scion, great care must be taken that they are 

 both placed as exactly in contact with each other as 

 possible, so that the line of separation of the wood and 

 bark should, in both stock and scion, be accurately 



