270 



MUTATION AND PLANT BREEDING 





Figure 5. — X-ray-induced mutations in Williams pear zoitlt irregularly 

 furrowed fruits. Three normal pears above. 



which two are shown in Figures 10 and 11. In Cox's Orange, Figure 



10, (gamma-irradiation), a whole branch carrying apples with dis- 

 tinctly increased color has originated. In Cox's Pomona (after pile 

 neutrons), one branch, represented by the first two rows in Figure 



11, is still sectorial in constitution, practically all fruits being sectored 

 with deep red. The other two branches formed on the same irradiated 

 tree, represented by the apples of the other two rows of Figure 1 1, are 

 quite normal. 



The chlorophyll-deficient shoot shown in Figure 4 (X-rays on 

 summer buds) is induced in the pear clone Striped Williams (43). 

 This Striped Williams, itself a spontaneous mutant very similar to 

 the one of Gardner et al. (38), is most probably an endochimaera 

 (Figure 12) that, besides "mutating" back to normal Williams, also 

 gives rise to numerous such white shoots when irradiated. Thus, these 

 changes are probably not true, original mutations, only tissue 



