30 Genetical and Cytological Studies on Pisum 



TABLE I. 



F^ ex B.A. X Th. 615Y26 showing the distribution of fertile and semifertile plants 

 among the three classes, homozygous and heterozygous rounds, and wrinkled. 



230 233 230 233 230 233 Total 



-cTi (FertUe 11 5 „ JFertUe 7 2 ^ (Fertile 10 6 41 



"^^jSterUe 2 1 ^ jSterUe 23 5 "^ jSterile 3—34 



In Table I, F^ families from 230 and 233 are set out according to 

 their gametic constitution for round wrinkled, and according to their 

 fertility or partial sterility. The pollen of a number of F^ plants was 

 examined, and whereas in 230 and 233 plants with half the poUen grains 

 empty had been found, in the rest of the families all the plants examined 

 had good pollen. At harvest the plants with 50 per cent, shrivelled pollen 

 were easily detected in the rows, for the ovules were also affected, and 

 each aborted ovule causes a constriction in the pod. The aborted ovules 

 also numbered approximately half the total number. It has since been 

 learnt that a constriction in the pod is always the result of gametic 

 failure, and is never brought about solely by zygotic failure (Pig. 2). 



In Table I a relation between the factors for round and wrinkled and 

 fertihty is shown, both in 230 (F^ ex D.A. rogue x Th. 7) and in 233 

 {F2 ex D.A. type x Th. 7). The total numbers for the two groups are: 

 RR, fertile 16, half-sterile 3; Rr, fertile 9, haK-sterile 28; rr, fertile 16, 

 half-sterile 3, giving 41 fertile : 34 half-sterile. The numbers point to 

 there being about equal chances of fertiles occurring among Rr as of 

 half-steriles among RR and rr, so that half the total number of plants 

 are fertiles, and half, half-steriles. This indication is confirmed by the 

 Fg families raised from the F2 haU-steriles (Table II). 



TABLE 11. 



Eight Fg families from half -sterile F^ plants; the first seven from 230/28, 

 the last from 233/28. 

 RR Rr rr Germina- 



