CH. v.] THE SAP. 177 



species on which it will take, and then moving it, 

 with some of the stock attached to another stock 

 still more remotely allied, that a graft may be made 

 to succeed, though supplied with sap from roots of 

 a very dissimilar species. Thus some pear scions 

 can hardly be made to unite with a quince stock ; 

 but if they be gi^afted upon a young shoot of a pear 

 that can be so united to the quince, and this young 

 shoot be aftei-wards inserted in a Cjuince stock, 

 they grow as freely as if inserted in a seedling pear 

 stock. 



The reason for this unusual difficulty in the way 

 of uniting kindred species arises from one or more of 

 these causes. First, the sap flowing at discordant 

 periods; secondly, the proper juices being dis- 

 similar ; or thirdly, the sap vessels being of inappro- 

 priate calibre. 



It is quite certain that the ancient Romans were 

 skilful gi'afters, for Cato, in his De Re Paisticd, gives 

 very full and accurate dkections on the art. If 

 it be true, as he asserts, in common with Varro, 

 Palladius, Virgil, Columella, Pliny, and other writers, 

 contemporary as well as more ancient, that they en- 

 grafted any kind of tree upon any stock, though of an 

 entirely different genus, as the apple upon the plane, 

 and the \due or the fig on the cherry, then, indeed, is 

 there another added to the list of lost arts. But 

 there is just reason for concluding that the ancients 



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