SAPROPHYTISM AND SYMBIOSIS 



777 



remaining attached to a small piece of bark is inserted in a T-shaped 

 incision in the stock (figs. 1085, 1086). The grafting of fruit trees is 

 of great commercial advantage, since most horticultural varieties do 

 not reproduce true to seed, and since even those varieties which " come 

 true " can be brought into bearing some years sooner by grafting than 

 by growing from seed. In the Rosaceae, grafting commonly is possible 

 only among closely related plants, as among the species of a common 

 genus; for example, plums, peaches, and apricots may be readily inter- 

 grafted, as may apples, pears, and quinces, while intergrafting is im- 



1086 



Figs. 1085-1088. — Budding and grafting: 1085, 10S6, shield-budding, the name 

 being derived Irom the shield-shaped piece of bark with the removed bud, b; 1086, the 

 stock in which a T-shaped incision (i) is made; the bud is then inserted and the whole 

 tied securely; 1087, 1088, cleft-grafting; 1087, represents two scions (6) wedge-shaped 

 below, which are inserted into a cleft in the stock (a), and then fixed in place by grafting 

 wax, as in 1088. — From Bailey. 



possible between apples and plums; sometimes closely related species 

 cannot be intergrafted (e.g. Prunus Padus and P Laurocerasus). In 

 the Solanaceae and the Compositae many instances are known where 

 different genera can be intergrafted, and cases are on record of inter- 

 grafting between different families. The latter phenomenon does not 

 seem strange, when it is remembered that successful grafting depends 

 upon similarities between vegetative characters, and that these are not 

 necessarily correlated with the reproductive characters upon which 

 plant relationships are based. 



At the juncture of the graft symbionts there is developed a callus, in 

 which xylem and phloem elements arise, uniting the two plants so that 

 they appear as one. However, in spite of the close union, the two plants 



