260 The Phenomena of Morphogenesis 



of dwarfing is that produced in some plants by growth from seeds that 

 have not been afterripened. A case of this sort in the peach where the 

 dwarfs retained their dwarf character when grafted on normal plants 

 was studied by Flemion and Waterbury ( 1945). The roots of such dwarfs 

 were able to support normal shoot growth, so that the seat of the dwarfing 

 seems to be in the shoot. There is no evidence of a stimulating substance 

 produced in the normal plant or of an inhibiting one in the dwarf. 



Some varieties are incompatible in grafting and so do not thrive to- 

 gether even though the graft union between them may be good or a 

 variety compatible to both is inserted as an interstock ( Sax, 1953, 1954 ) . 

 Tukey and Brase present evidence that not only the character of stock 

 and scion and their compatibility are important in determining tree size 

 but also the effect of environmental factors on each partner and on their 

 combination. 



Aside from purely quantitative effects of stock on scion in horti- 

 cultural plants, other traits have been reported to be transmitted from 

 one to the other. McClintock ( 1937) found that leaves of the Grimes apple 

 grafted on Virginia crab stock have a greater green weight and are 

 physiologically different in some respects from those of the same va- 

 riety on other stocks. Blair (1938) grafted Bramley Seedling apple on 

 French crab but in a number of cases inserted between stock and scion 

 a 9-in. piece of one of three other varieties, Mailing II, IX, and XIII. Even 

 though here stock and scion were the same, the effect of these middle 

 pieces on the tree that grew out of them was markedly different in 

 each case, as shown in leaf poise, general habit of branching, leaf color, 

 and time of defoliation. The effect of the various middle pieces on the 

 root was also evident. Rogers, Beakbane, and Field (1939), however, 

 found that intermediate pieces from different sources had relatively little 

 effect on the rootstocks. By grafting apple scions from various sources on 

 roots, Swarbrick and Roberts (1927) found that the character of the 

 root tended to be like that of the variety which contributed the piece of 

 stem just above it, whether this was scion or middle piece. Amos, Hatton, 

 and Hoblyn ( 1930 ) dispute this conclusion and believe that the effect of 

 scion on root is simply quantitative. 



In citrus fruits Halma ( 1934 ) reports that Eureka lemon scions grafted 

 on sour-orange roots greatly modify the form and color of the latter. 

 In the reciprocal graft, only the color of the root was changed. These 

 changes were observed in grafted but not in budded trees. 



Early work on the stock-scion relationship is reviewed by Swarbrick 

 (1930), and Garner (1949) has presented the subject from a practical 

 point of view. 



The mixture of tissues by grafting and the relation between the graft 

 partners pose problems of wider interest than for horticulture alone. It 



