330 Plant Physiology 



of trunk above and below the region of the graft, and 

 this difference becomes more pronounced with age. Im- 

 proper, or difficult, union, if it does not result in im- 

 mediate death, will inhibit the transfer of material be- 

 tween shoot and root, and may lead to an abnormal 

 swelling in the region of the union. 



194. Scion propagation. As referred to in the dis- 

 cussion of reproduction, vegetative propagation is often 

 desirable, and propagation by buds or scions possesses a 

 variety of advantages, some of the most important of 

 which are as follows : (1) for the maintenance of varietal 

 characters, especially when the plant is of uncertain or 

 hybrid origin, when a return to the seed would yield an 

 unknown progeny, (2) for the more rapid propagation of 

 desirable species and varieties, and (3) for certain advan- 

 tages of growth or hardiness which may result by placing 

 the scion on roots other than its own. 



195. Relation of stock to scion. Commonly there is 

 believed to be relatively little direct formative influence 

 of the stock upon the scion, and an analysis of the facts 

 thus far demonstrated makes it clear that, as a whole, the 

 relations between stock and scion are very complex. The 

 effect of the stock upon the total amount of growth is 

 most evident in dwarf varieties, such varieties of the pear, 

 for example, are obtained by grafting pear scions upon 

 quince stocks. The scion is then furnished, in all proba- 

 bility, by a root system less active in absorption, and the 

 effects of this are evident not only in diminished size, but 

 also in slight modifications of leaves and sometimes of 

 fruit. Waugh has called attention to certain differences 

 in vigor of growth as well as in size and serration of leaves 



