in?rrDiNc systi-ms 



is enough to fertilize every egg and so give a full crop of fruit. 

 This second type, half-and-half, is always found in the relationship 

 o( parent and offspring. 



^1^2 



'<% 



Vs 'z%',% 



c/ 



2 



{EARLY BLACK 

 BEDFORD PROUf/C 

 BLACK TARTARIAN 

 EARLY RIVERS 

 fSCHRECKEN 

 FRO GM ORE B/C. 

 WATERLOO 

 j NAPOLEON 

 \ EMPEROR FRANC/S 

 [ KENTISH B/C. 

 ( ELTON 

 \g OYER NOR WOOD 



X 



I 



Ha 









Ui Q) OQ li] O) 



5 1 



§ 



I 

 I 



Fig. 58. — The compatibility relations of 12 varieties of sweet cherry, falling into 

 5 incompatibility groups. + indicates successful pollination, — unsuccessful pol- 

 lination, and a blank that the pollination has not been tried. The compositions of 

 the varieties relative to the S gene are shown above (after Crane and Lawrence, 

 1947). 



These results give us the clue to the genetic problem. The half- 

 and-half types of pollen are obviously produced by single gene 

 heterozygotes. Since the parent's style rejects all its own pollen and 

 only half that of its offspring, the rejected pollen must be that which 



244 



