214 PROPAGATION. 



edly controverts the idea that the new zone of wood 

 is formed by fibres, which descend from the buds of 

 the higher parts of the tree ; and secondly, we may 

 state our opinion, that the result showed that the 

 vital envelope of the sycamore was removed with its 

 bark, and that of the red maple put in its place, 

 otherwise no new wood of the latter could have been 

 formed beneath. Had the bark of the red species 

 been placed on the undisturbed envelope of the syca- 

 more maple, supposing this practicable, the new-formed 

 wood would have been that of the last-named tree. 



The difficulty about change of the colour of leaves 

 is easily solved by saying that the taint (or disease as 

 it is considered to be by botanists) is carried down by 

 some partial subsidence of the sap. And though 

 there may he rational doubts of the possibility of sap 

 convey in g forms from one part of the plant to another, 

 it may be admitted that it is capable of conveying 

 those chemical oxygenating qualities which may 

 change green to yellow coloured leaves. 



Certain influences have been attributed to the 

 stock as either improving or deteriorating the fruit 

 of the graft. It is said that pears from a quince stock 

 are more austere than such as are produced by the 

 common pear stock ; and there are other accounts 

 on record of apples being altered by the stocks on 

 which they are worked. But none of these reports 

 have been so far confirmed as to have any rule of 

 practice founded upon them. One eifect of double 

 working fruit trees has been proved by nurserymen ; 



