Tissue Mixtures 263 



tubers when they were used as seed. Somewhat similar results are re- 

 ported by Gregory (1956), who also found that the tuber-forming stimu- 

 lus could be transmitted from all parts of the shoot by grafting. 



Some recent experiments on the graft transmission, or lack of trans- 

 mission, of plant traits are the following: 



In English ivy (Hedera helix) Doorenbos (1954) grafted scions from 

 the juvenile type (with lobed leaves) onto the adult, upright, flowering 

 form and found that the latter often lost its abilitv to flower and 

 showed other juvenile traits. 



Popesco (1949) reports that when Sophora japonica, a woody peren- 

 nial leguminous plant, is grafted to the common bean, the bean flowers 

 15 to 20 days later than it otherwise would and becomes perennial in 

 habit. 



Hybrids between Meliotus alba and M. dentata are deficient in 

 chlorophyll because of some gene interaction and die in a few days. If 

 such hybrids are grafted to sweet clover, however, they grow well, 

 flower, and bear seed (W. K. Smith, 1943). 



In spruce (Picea abies), Muller-Stoll (1947a) examined grafts of shoots 

 from the tops of old trees on young seedlings. After 3 years these 

 flowered abundantly, far earlier than they would have done otherwise. 

 Only female cones were produced, presumably because the branches 

 used as scions were from the top of the tree, which bears chiefly female 

 cones. This localization the author interprets as an instance of topophysis. 



Many cases have been described of the effect of stock on fruit size 

 in the scion. Bitters and Batchelor ( 1951 ) report such a case in the orange, 

 where Washington navel oranges were grafted on 32 different root- 

 stocks and Valencia on 26. Differences were found between stocks in 

 their effects on fruit size in the scion. These differences are not related 

 to those in tree size or in number of fruits. 



An incompatible graft is reported in cucurbits by Wellensiek (1949). 

 Grafts of muskmelon on Cucurbita ficifolia grew for a time and then 

 suddenly wilted and died. Muskmelon as an interstock between cucum- 

 ber and C. ficifolia has the same effect. If a few leaves are left on the lat- 

 ter, however, the graft with muskmelon is successful. The reciprocal graft 

 thrives, so that incompatibility is in only one direction. The author 

 believes that muskmelon fails to give the stock of C. ficifolia a sub- 

 stance necessary for its growth and that this is provided if a few leaves 

 are left on it. 



Yampolsky (1957), in the dioecious Mercurialis annua, grafted male 

 and female plants together in a variety of ways but found no alteration 

 in the sexual character of either. 



Of particular interest for genetics are those cases where there is a 

 known genetic difference between scion and stock. Hijoscijamus niger, 



