406 



PLANT PHYSIOLOGY 



varieties of apples may be grafted into the crown of a wild apple 

 tree, and each of them will preserve all its specific properties and 

 will produce fruit of a quality characteristic of the particular 

 variety. Preservation of the characteristic of a variety is only 

 possible because the reciprocal effects between the stock and scion 

 are very insignificant. 



''Chimeras/' which at one time were called ''graft hybrids," 

 supply the most evident proof of the fact that each constituent 

 of a graft preserves its own characteristics in spite of their close 

 connection. They have been studied in detail by Winkler. By 

 chimeras are meant plants that are sometimes obtained as a 



^Xrf 



12 3 4 



Fig. 127. — Black nightshade and tomato chimeras. 1, Leaf of a normal black 

 nightshade; 2, leaf of an antichnal chimera, 3, leaf of a periclinal chimera; 4, leaf 

 of the tomato {redrawn from Winkler) . 



result of grafting one plant upon another and securing a com- 

 bination of tissues of both. At first it was supposed that in 

 these cases a fusion of cells had taken place, similar to that 

 occurring in fertilization; hence the name, graft hybrids. Wink- 

 ler's investigations, however, have shown that this is not so. 

 He determined with accuracy both the nature of chimeras and 

 the method of obtaining- them. Chimeras are easily secured 

 from various species of Solanum, especially Solarium nigrum and 

 Solarium lycopersicum. The latter may be joined to. the former 

 by cleft grafting. A stump of the nightshade plant, Solanum 

 nigrum is split, and into it is inserted a wedge-shaped tomato 

 scion. They are then left to unite. When they have grown 

 together, the scion is cut near the union. This results in the 

 formation of adventitious buds on the cut surface. Those formed 

 from the surface of the stump will develop shoots of Solanum 

 nigrum, while those rising from the wedge will produce tomato 

 shoots. Sometimes buds are formed at the point of junction of 



