Tissue Mixtures 265 



and darker leaves. When grafted as a scion on A. siculum stock, the 

 stem is somewhat . shorter and bears abnormal flowers but is otherwise 

 unchanged. The tomato mutant is dwarf, has scanty chlorophyll, and 

 lacks branches and flowers. When grafted as a scion on tomato stock 

 its chlorophyll remained deficient but its growth became approximately 

 normal as to height, branching, and flower development. The particular 

 interest of these cases lies in the fact that the various effects of a gene 

 here seem to be separated, some of them passing across the graft union 

 and others not doing so. Such material offers a favorable opportunity 

 for the study of gene action. 



Rick (1952) found a tomato mutant, wilty dwarf (wd), which differed 

 from normal in having fewer and shorter internodes, smaller leaves, thin- 

 ner stems, blue-gray leaf color, and a tendency to wilt in summer. This 

 was grafted in various ways on homozygous normal ( + ) lines differing 

 from wd in only this one gene. Control grafts of wd on wd and of + on -}- 

 showed no modification. Reciprocal grafts of -f- on wd and wd on + had 

 their leaf dimensions and stem lengths shifted markedly toward the 

 character of the stock. In double graft combinations, wd/ -\- /wd and 

 -h /wd/ +, the top scion was unaltered but the middle piece was changed 

 in the direction of the stock. The author concludes that the effect of 

 stock on scion here is not due to factors in the stem or leaves but in the 

 root system of the stock. 



Kostoff ( 1930Z? ) observed irregular meioses in the pollen cells of tobacco 

 grafted to other genera, and such scions produced much abortive 

 pollen. If flowers on them were selfed, various chromosomal aberrants 

 appeared in the progeny but none in the controls. 



In Petunia, Frankel ( 1956 ) grafted fertile scions to stock showing 

 cytoplasmic male sterility and found sterility in the offspring of such 

 scions, suggesting that cytoplasmic sterility determinants had passed 

 from stock to scion. The author recognizes the possibility that nutri- 

 tional changes induced by grafting may have been responsible for these 

 effects. 



Wagenbreth ( 1956 ) made grafts between a number of species of 

 legumes and found by inoculation experiments that, although bacteria 

 specific for the stock would produce nodules in such plants, bacteria 

 specific for the scion would not. 



Common experience has shown that strictly qualitative characters such 

 as shape are usually gene-controlled and not influenced by grafting, 

 despite early claims to the contrary. A few pieces of positive evidence, 

 however, have been reported in recent years. Heinicke (1935) observed 

 that Mcintosh apples borne on defoliated scions grafted into Northern 

 Spy, and thus grown from material produced by Northern Spy leaves, 

 tended to be modified in the direction of the latter variety. Southwick 



