418 BULLETIN No. 127. [August, 



8. GRAFT-HYBRIDS 



We have in graft-hybrids another method in which there may be 

 a possibility of an improvement of the potato. 



There is still a great deal of argument as to the authenticity of 

 graft-hybrids which have been reported. The negative reasoning 

 being chiefly theoretical, owing to their present inexplicability. 



Darwin (21) collected a large number of cases where asexual 

 hybrids of the potato seem to have been made. He himself was 

 fully convinced as to their authenticity although he recognized the 

 fact that the scoffer might attribute them to bud variation induced 

 by the graft. He argues that the variation was always between the 

 parent forms. 



Daniel (19, 20) who has made by far the most extended study 

 of grafts, says that, "While formerly it was considered that grafted 

 scions lost none of their own characteristics and acquired no new 

 ones from the stocks on which they were grafted, recent work 

 indicates that this view must be modified." He states that hybrid- 

 grafts can be fixed and propagated ; and mentions the Edouard Le- 

 fort potato produced by vine graft of Majolin and Imperator and 

 partaking of the character of each. He believes, however, that 

 asexual hybridization is neither constant, regular nor very frequent. 



Biffen (n) grafted tubers with different characters, and while 

 convinced of the authenticity of the phenomenon, he states that 

 "Tubers in which two types are blended, never occur." In halving 

 the tubers transverely, each portion was indistinguishable from one 

 of its parents. Each half of the tuber showed all the characters of 

 one parent and not certain dominant ones. The graft-hybrid was in 

 this respect different from the seed hybrid. 



There is at present no cytological explanation of such a phe- 

 nomenon, but from the apparent ease with which hybrid-grafts are 

 made, or at least by which bud variations are caused through such 

 stimulus, this seems to be a very interesting field for investigation. 

 If in potato improvement we could in time learn to make a reason- 

 able percentage of successful hybrids and the characters would blend, 

 it might settle the quandary in which we are at present, in trying to 

 get crosses with many of the excellent varieties which produce little 

 or no viable pollen. On the other hand, if it finally proves that 

 there is not a true hybrid formed, this method may still prove valu- 

 able as a means of obtaining bud-mutations. 



