114 University of California Piiblications in Botany [Vol. 5 



weights, but seed which is uniform in size and in weight for 

 each parent — we obtain from the matured ovaries seed ap- 

 proximately 1/4 of which is heavy, 14 ^^ which is light, and i/^ 

 of which is intermediate in Aveight between the heavy and light 

 seed. Now upon growing the F2 plants from the heavy weights 

 of this Fi hybrid seed, we obtain 31 plants, the appearance of 

 which approximates that of the macrophylla parent as against 

 seven plants which resemble virginica. Among the Fo individuals 

 produced by the light seed, eleven plants resemble virginica 

 and six plants resemble macropliylla. Finally, from the seed 

 intermediate in weight, approximately 25 per cent of the F, 

 plants resemble one parent and 25 per cent the other parent. 

 Thus the fact of segregation, to the extent to which it has taken 

 place, becom.es apparent when the Fo plants are grown, in that 

 for the heavy seed one parent is "dominant," for the light seed 

 the other parent is "dominant"' and from among the medium 

 weight .seed 50 per cent each of the two parents are produced. 

 In addition the "dominance" seems to follow the weights of the 

 parental seed in each case, since the heav3'-seeded parent appears 

 in Fo in greatest number among the plants grown from heavy 

 seed and the light-seeded parent from the light F^ hybrid seed 

 (see, in this connection, Waldron, 1910, p. 56 ; also Harris, J. A., 

 1912 a). 



In this connection the following suggestion is tentatively ad- 

 vanced. There may be such an organization of the developing 

 pollen from the anthers of the hybrid in F^ that the generative 

 nucleus in each mature pollen grain bears one of two influ- 

 ences. The first constitutes a "determiner" (Davenport, '08), 

 functioning to produce the outward appearance of the macro- 

 pliylla parent. The second influence may be one which functions 

 for the production of the outward characteristics which dis- 

 tinguish the virginica parent. The tube nucleus may, like- 

 wise, bear any one of two influences. The first is one which 

 functions for the production of heavy seed, after its union 

 with the fusion nucleus in the embryo sac and the second 

 functions for the production of light seed. Corresponding 

 conditions may be present within the embryo sac in the case 

 of the e^^ nucleus and in the case of the fusion nucleus 



