1912] Goodspeed: Nicotiana Hybrids 113 



the presence of a Mendelian ratio within our limited experi- 

 mental material, and the following brief discussion in no way 

 attempts to exclude the possibility of such an interpretation. 

 Our effort is primarily to ally ourselves with those who feel that 

 "what is urgently needed is an accurate description of the 

 various waj's in which the characters of domesticated animals 

 and plants are inherited. It will be time enough to interpret 

 them when our knowledge of them is a great deal more perfect 

 than it is at present" (Darbishire, 1911, p. 240). 



The experimental results in general seem capable of explana- 

 tion on the assumption that we are dealing here, in the case 

 of the seed produced by the F^ hybrid, with an infinite series. 

 By growing plants from the two extremes, the heavy and the 

 light seed, we have produced a high percentage of plants re- 

 sembling the two parents — one parent from the heavy seed and 

 one parent from the light seed. Again, by using the medium 

 weights of seed we produce 50 per cent of plants intermediate in 

 appearance and 25 per cent each of plants resembling each of 

 the two parents. The fact that approximately 50 per cent of 

 the plants from each of the two extremes were "intermediate" 

 or "blends" may be due to the inaccuracy of the weighing or to 

 the small number of F^ generation plants grown. In other 

 words, had it been possible to weigh each seed separately or to 

 grow 1000 Fo plants, the percentage of plants from heavy seed 

 resembling N. Tabacum var. macrophylla and of plants from 

 light seed resembling N. Tabacum var. virginica, might have 

 been far higher. 



From another point of view, the occurrence in the F^ hybrid 

 seed of three readily distinguishable divisions according to weight 

 and size is significant, and especially so when we find a rather 

 marked uniformity in weight and in size among the seeds of both 

 parents. The possibility suggests itself that whatever segrega- 

 tion there may be has taken place in such a manner within the 

 ovary of the F^ hybrid that it (the segregation) becomes apparent 

 only in the physical characteristics of the seed which the F^ hybrid 

 plant produces. Thus on close fertilization of the F^ hybrid plants 

 of the cross N. Tabacum var. macrophylla ^yi N. Tabacioii var. 

 virginica 1^— these two parents producing seed of different 



