CHAPTER XXII 

 GRAFT-HYBRIDS AND OTHER CHIMERAS 



A graft-hybrid, as its name implies, is a shoot or plant which is pro- 

 duced by grafting one kind of plant upon another and whose characters 

 are intermediate between the characters of the two components. None 

 of the so-called graft-hybrids are really hybrids at all; they are merely 

 mixtures of tissues from two kinds of plants which can live in unison. But 

 each kind of tissue is distinct in its every cell, i.e., there has been no fusion 

 of cells or blending of germ plasm as in the case of sexually produced 

 hybrids. Some difference of opinion still exists regarding a single case 

 which will be referred to again, but the above statement certainly applies 

 to all other graft-hybrids that have been investigated. As Buder says, 

 a graft-hybrid is nothing else than a special form of graft-symbiosis. 

 Thus all graft-hybrids are chimeras (p. 271). A conception of how chi- 

 meras originate naturally may be gained by learning how graft-hybrids 

 have been produced experimentally. 



Tomato -nightshade Graft-hybrids. Some members of the night- 

 shade family are easily grafted even though they belong in different 

 genera. Thus it is possible to double work nightshade on tobacco on 

 tomato. Reciprocal grafts of tomato and potato are easily made and 

 Heuer has grafted tomato on egg plant and tomato on bittersweet. 

 In recent years Winkler has produced four different chimeras and another 

 form which he considers a true hybrid by grafting tomato on nightshade 

 or vice versa. The four Solanum chimeras are shown in Fig. 151. Wink- 

 ler's method is to graft on a scion by one of the ordinary methods and 

 soon after it has united with the stock to cut it off taking pains to make 

 the cut pass through the united tissues of stock and scion as shown in 

 Fig. 152. Most of the adventitious buds pushed out are either night- 

 shade or tomato. But occasionally a bud will be formed on or near the 

 line of union. In such cases either one of two combinations of the graft- 

 components may result depending on the relations of the two kinds of 

 callous tissue. If the two masses meet as in a of Fig. 153, the young 

 shoot will consist of sectors of nightshade and tomato, but should one of 

 the cell-masses grow over the other tissue producing the condition shown 

 in 6, the young shoot in this case will be composed entirely of tomato 

 inside but will have an envelop of nightshade cells surrounding it. The 



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