64 THE NURSERY-BOOK. 



sing sex in dioecious trees, or a variety with more potent pollen 

 as practiced in some of the native plums. All these uses of 

 graftage fall under three heads 1 i. Ta perpetuate a variety. 

 z. To increase ease and speed of multiplication. 3. To pro- 

 duce some radical change in nature or habit of cion or stock. 



Probably all exogenous plants those which possess a distinct 

 bark and pith can be grafted. Plants must be more or less 

 closely related to each other to allow of successful graftage of 

 the one upon the other. What the affinities are in any case can 

 be known only by experiment. As a rule, plants of close 

 botanical relationship, especially those of the same genus, graft 

 upon each other with more or less ease ; yet this relationship is 

 by no means a safe guide. A plant will often thrive better upon 

 a species of another genus than upon a congener. The pear, 

 for instance, does better upon many thorns than 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 

 cannot 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 out- 

 grows the stock a weak tree is the result. 



Graftage can be performed at almost any time of the year, 

 but the practice must be greatly varied to suit the season and 



