268 KARL B. KRISTOFFERSON 



reciprocal crosses — about 20 individuals — were of the same 

 shape. 



In Fn a segregation appeared in plants with normal green leaves 

 and in plants with white-spotted. The latter ones were white-spotted 

 in a very different degree; some petals were almost pure green and 

 other were strongly white-spotted just as in the case of selfed albo- 

 maculata. 



From the cross between normal green and albomaculata 209 nor- 

 mal green and 65 white-spotted were obtained in F^; thus the ratio 

 3,22 : 1 or pro 4, 3,05i : 0,949. The theoretical value is 3 : 1 4= 0,i048. The 

 observed value lies thus within the limits of the theoretical. 



In the reciprocal cross, where consequently the albomaculata- 

 form w^as the female parent, 153 normal green and only 12 albo- 

 maculata were obtained. The observed ratio was 12,75 : 1 or pro 4, 

 3,709:0,291. The theoretical ratio is 3 : 1 d=0,i356. The deviation was 

 more than thrice its standard error; thus it exceeds the statistically 

 allowed range for a monohybrid segregation. The observed ratio pro 

 16 is 14,8364 : 1,1636. Here the deviation is less than the standard 

 error. 



Thus, it appears as would one of the reciprocal crosses give a 

 monohybrid segregation and the other a dihybrid one. Of course, 

 these different segregations may be explained by the assumption of 

 different Mendelian factors in the germ cells of the green parent. If 

 this plant had one factor for normal green in the female germ cells 

 and two factors in the male germ cells, the albomaculata-form being 

 recessive in both, the segregation would correspond to the observed 

 one. The explanation of the matter is much more simple, however. 

 The 7^\-generation of the cross normal green X albomaculata was 

 grown on the experimental field together with the other cultures. As 

 it was not sufficiently large I was obliged to plant the reciprocal cross 

 on a plot a little way off. As I was out travelling a great part of the 

 summer 1917 when Fo was grown and therefore unable to look over 

 the work on the field, this plot was forgotten at the weeding of the 

 experimental field. When I returned I found this culture quite over- 

 grown of weeds. About half of the plants had died. It is obvious 

 that the white-spotted ones, being much weaker than the normal 

 green, would first become eliminated. 



Thus the difference between normal green and white-spotting 

 w^ould be due to one single factor A. When this factor is present 

 the plant becomes green; when absent it becomes white-spotted. The 



