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University of California Puhlicaiions in Botany [Vol. 5 



two adjacent plants of IIF0H24P34, one tall and of the general habit 

 of alha, and the other short and of the general habit of macrophylla. 

 The classification for height is given in table 18. Obviously no satis- 

 factory Mendelian formulation can be deduced from these data. 



As regards flower color, however, the classification is more definite. 

 Four more or less distinct shades were distinguishable, viz., red, pink, 

 light pink, and white. The pink and light pink shades merged into 

 each other, consequently they have not been separately recorded in 

 table 18. Bearing in mind the previous behavior of red and pink, as 

 shown in the angustifolia-macrophylla and calycina-virginica series, 



TABLE 18 



¥2 SEGREGATION IN THE ALBA-MACROPHYLLA SERIES. 



it would appear that we are here dealing with dihybrid populations 

 in which a pair of allelomorphs for color versus white is concerned in 

 addition to that pair upon which the contrast of pink versus red was 

 found to depend. The pair of allelomorphs for the pink versus red 

 contrast has been represented by R and r, respectively. If we repre- 

 sent the contrast of color versus white by W and w, respectively, the 

 two parents in this series would possess the following genotypes : 



Alia = RRww 



Macrophylla = rrWW 



The light pinks of the previous series would then be RRWW, and the 

 factor R might be regarded as a dominant diluter. According to this 

 formulation, F^ of the alha-macrophylla series would be RrWw, pink, 

 and Fo should segregate in the ratio 3 red : 9 pink : 4 white. The 

 expected result in the classification of ninety-seven plants in whole 

 numbers is 18 red : 55 pink : 24 white. Agreement is thus fairly close. 

 A check on the results above noted for the 1911 sowings of the Fo 

 population was made by growing in 1916, five additional Fo popula- 



