THE NATURE OF GRAFT-HYBRIDS 



PROFESSOR DOUGLAS HOUGHTON CAMPBELL 

 Stanford University 



The possibility of hybrids arising as the result of 

 grafting long has been a mooted point and the subject has 

 given rise to much discussion. 



The history of the small number of graft-hybrids that 

 have hitherto been recorded is small and is not as com- 

 plete as might be wished; indeed it has been claimed re- 

 peatedly that these supposed graft-hybrids are not really 

 such but have been produced by the ordinary method of 

 cross-fertilization. The most famous of these graft- 

 hybrids is the much discussed Cytisus Adami which 

 originated at Vitry near Paris about 1826. This was 

 said to have been the result of grafting Cytisus pur- 

 puras upon C. laburnum. A series of supposed graft- 

 hybrids is also recorded resulting from grafts between a 

 thorn, Cratcpgus monogyna, and the medlar, Mespilus 

 germanicus. Throe of these graft-hybrids were secured 

 by Bronvaux. The hybrids in this case were not all alike 

 and were given special names and the genus Cratcego- 

 mespilus was proposed for these bi-generic hybrids. 



Of the recent opponents of the graft-hybrid theory the 

 best known is the distinguished botanist Professor E. 

 Strasburger, of Bonn. Strasburger made a careful cyto- 

 logical study of Cytisus Adami which has been retained 

 in cultivation ever since its origin some eighty-five years 

 ago. Strasburger came to the conclusion that Cytisus 

 Adami was a real sexual hybrid and not a graft hybrid. 

 He believes that if the latter were true the nuclei of the 

 hybrid would show a double number of chromosomes. 

 This, of course, implies that in hybrids arising otherwise 

 than sexually, assuming that a nuclear fusion would pre- 

 cede the formation of such a hybrid, there would be no 

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