REPRODUCTION BY STEMS AND LEAVES 89 



covering all exposed parts well with grafting wax. Root graft- 

 ing has the advantage that it results in a tree with trunk and 

 branches wholly of the desired variety of apple. Tongue 

 grafting of small branches does not interrupt the growth of 

 the tree and is done with very little trouble. Top grafting is 

 mainly resorted to in order to renew old trees that are not 

 bearing the desired variety of apple. 



The main object of budding and grafting is to propagate 

 the varieties of fruit which the horticulturist desires. This 

 cannot be done merely by growing seedling trees, since every 

 seedliag of hundreds grown from any valuable kind of apple 

 or pear may differ from all the others of the same lot and not 

 one of them be worth cultivating. 



Grafting often succeeds on plants of different species,^ as 

 the peach on the plum, the apple on the pear, and the pear 

 on the quince. Sometimes it succeeds between different 

 genera i of the same family,^ as the tomato on the potato and 

 the Spanish chestnut on the oak. 



Many technical details must be attended to in order to bud 

 or graft successfully, and these are best learned from a practical 

 horticulturist. 



80. Reproduction by leaves. Not very many plants can re- 

 produce themselves by means of their leaves. The best-known 

 examples are begonias, which are largely propagated by cut- 

 ting off leaves, slitting them, and then laying them on moist 

 sand under a bell glass until buds and roots are produced 

 at one or more points of the cut surface. A not uncommon 

 greenhouse plant of the Live-forever family, the Bryophyllum, 

 is still more easily propagated, as the leaflets readily produce 

 buds and roots at the notches along their margins when placed 

 on moist earth. 



1 For the definition of the terms "species," "genus," and "family," see 

 Chapter X. 



