R P. Gregory 97 



used, we are justified in assuming that all the other races which have 

 been used possess the factor F ; consequently, crosses between the full- 

 coloured stem and the faint colour merely exhibit the segregation of 

 the factor R, the effect of Q, which is present in all the offspring, 

 being masked when R is also present (Table, p. 98, III.). The same 

 applies to the crosses between the full colour and the green stem, 

 but in this case one-third of the offspring have clean green stems 

 (Table, p. 99. IV.). 



In the F^& from crosses between " Snowdrift " and races with fully 

 coloured stems " Sirdars " occur ; and if the factors inhibiting flower- 

 colour be absent, the F^ is found to contain approximately, in every 16 

 plants, 9 with fully coloured stems and flowers, and 3 " Sirdars " ; while 

 of the remaining 4, 3 may have faint colour in the petioles, or they may 

 all be devoid of colour in the stem, according to the presence or absence of 

 the factor for faint colour in the coloured parent. The total numbers 

 obtained in these crosses (Table, p. 99, V. C) show some divergence 

 from the expectation set forth above, in giving an excess of " Sirdars." 

 The divergence is however almost entirely due to the results obtained 

 from the first two families raised, which gave 142 full, 75 "Sirdar" 

 and 67 faint and green. In the later experiments a close approximation 

 to the theoretical proportions has been maintained, the numbers 

 obtained being 329 full, 110 " Sirdar," 134 faint and green. In crosses 

 between " Snowdrift" and red-stemmed dominant whites, the "Sirdar" 

 character cannot be determined with any accuracy in those offspring 

 which have white flowers. In these F^s the observed numbers of full- 

 coloured stems and light stems (including " Sirdars ") approximates very 

 closely to the expected ratio of 9 : 7 (Table, p. 99, V. B). 



There remain however cases in which the 9 : 7 ratio is clearly 

 indicated in F^s from which " Sirdars " are absent (Table, j). 98, I.). 

 Only two such cases have been met with, but the result strongly 

 suggests that, in Primula, as elsewhere, at least two complementary' 

 factors are necessary for the production of colour. In one of the cases, 

 the character of faint stem- colour was not recorded separately, and we 

 only know that the family consisted of 51 fully coloured and 33 light 

 or green stems. In the other case, the coloured parent was a dominant 

 white, and the offspring consisted of 49 fully coloured, 13 with colour 

 in the petioles, and 25 devoid of colour, or 49 fully coloured, 38 light 

 stems (.9 : 7 = J^8•9^ : 38-06). In so far as reliance can be placed upon 

 the distinction between plants with faint colour in the petioles and 

 those devoid of colour, this result further suggests that one comple- 



