THEORY OF GRAFTING 85 



apply with a stiff bristle brush. On exposure to the air 

 the alcohol evaporates and the wax hardens. 



Theory of Grafting. The fundamental principle on 

 which the practice of grafting is based is purely a question 

 of plant physiology. Plants have a more or less definitely 

 organized circulatory system. The food is taken in through 

 the roots and passes upward through the outer or sap 

 wood. It is then carried into the leaves where it is converted 

 into the more highly organized compounds and made avail- 

 able for plant growth. Part of this material passes down 

 the trunk of the tree on the line between the bark and the 

 wood. This constitutes the return flow of sap and is known 

 as the cambium layer. This layer forms the wood cells 

 on the inside, and the bark cells on the outside, and the point 

 from which a union must be made when a cion is inserted. 



When a union is made between two different varieties 

 of fruit this does not change the function of the cells of 

 either stock or cion. Each cell performs its usual duties 

 up to the point where the sap is passed on to the other 

 wood. The work is then completed by the cells of the cion. 

 If the cells of the stock are not able to supply the sap as 

 fast as the cion can use it, the resulting tree will be dwarfed. 

 This fact is made use of in nursery practice by grafting 

 pear on quince stock to reduce the stature of the tree. 

 If the cells of the cion are radically different from those 

 of the stock, they will not be able to utilize the sap and no 

 union will result. The limits of grafting then, depend more 

 upon the closeness of the relationship of the stock and cion 

 than upon any other one thing. 



Any one who is doing grafting work will have several 



