86 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



type (both red and yellow) and 42 of the rogue type (both red 

 and yellow). On the assumption that we have to deal with a simple 

 3 to I Mendehan segregation, the expectation would be 107 normals 

 and 36 rogues, and the numbers obtained are sufficiently near to 

 the expectation to suggest that simple segregation is taking place. 



The case is a particularly interesting one, for the differences between 

 the two forms are marked and complex, and the fact that the domi- 

 nance is complete is in itself very interesting. As we have said, the 

 change from maleness to femaleness is a rare one, but the results of 

 the experiment seem to show that in Cheiranthus femaleness is recessive 

 to maleness. 



The persistence of this rogue type in small numbers, even though 

 now great care be exercised in eliminating them from plants growing 

 for seed, may be readity understood, if we assume the rogue on 

 its first occurrence produced seed.* The seeds produced by it must 

 have been hybrids, since the rogue itself produces no pollen, but they 

 would doubtless have been sown among others from perfectly normal 

 plants, and the culture would consist of many true normals, and a few 

 hybrids, apparently normal, and quite indistinguishable from the 

 normals in structure. The normals would far outnumber the hybrids, 

 and the chances of interpolHnation among the latter would be cor- 

 respondingly small, with the result that, while hybrids would be pro- 

 duced with each succeeding generation, rogues — the pure recessives — 

 would rarely appear. 



We may show this graphically by the following diagrams, where 

 N stands for the dominant normal, r for the recessive rogue. 



Crossing the rogue with the normal (which can be done only one 

 way) we have : 



N (? X r ? 

 I 



Nr ^. 



(hybria) Fi 



Seed may be produced by the Nr plants either by intercrossing among 

 themselves or by crossing from the normals, and the results will be 

 different in these two cases : 



I. Where the hybrids intercross: 



Nr X Nr 



NN ^ Nr ? Nr ? rr ? 



(normal) (hybrid) (rogue) 



and rogues will reappear in the proportion of one to three, two of 

 which are hybrids. 



* Rogues allowed to grow among plants produce a few seeds without artificial 

 pollination. 



