78 GRAFTAGE. 



upon the apple. Sometimes plants of very distinct genera 

 unite readily. Thus among cacti, the leafless epiphyllum 

 grows remarkably well upon the leaf-bearing pereskia. It 

 should be borne in mind that union of tissues is not a proof 

 of affinity. Affinity can be measured only by the thrift, 

 healthfulness and longevity of the cion. The bean has been 

 known to make a union with the chrysanthemum, but it 

 almost immediately died. Soft tissues, in particular, often 

 combine in plants which possess no affinity whatever, as we 

 commonly understand the term. Neither does affinity refer 

 to relative sizes or rates of growth of stock and cion, 

 although the term is sometimes used in this sense. It can- 

 not be said that some varieties of pear lack affinity for the 

 quince, and yet the pear cion grows much larger than the 

 stock. In fact, it is just this difference in size and rate of 

 growth which constitutes the value of the quince root for 

 dwarfing the pear. When there is a marked difference in 

 rate of growth between the stock and cion, an enlargement 

 will occur in the course of time, either above or below the 

 union. If this occurs upon the stem, it makes an unsightly 

 tree. If the cion greatly outgrows the stock a weak tree 

 is the result. 



General Methods. Graftage can be performed at almost 

 any time of the year, but the practice must be greatly varied 

 to suit the season and other conditions. The one essential 

 point is to make sure that the cambium layers, lying 

 between the bark and wood, meet as nearly as possible 

 in the cion and stock. This cambium is always present in 

 live parts, forming woody substance from its inner surface 

 and bark from its outer surface. During the season of 

 greatest growth it usually occurs as a soft, mucilaginous 

 and more or less unorganized substance, and in this stage it 

 most readily repairs and unites wounded surfaces. And for 

 this reason the grafting and budding of old trees are usually 

 performed in the spring. Later in the season, the cambium 

 becomes firmer and more differentiated, and union of woody 

 parts is more uncertain. It is also necessary to cover the 



