1913] EAST—CROSSES OF NICOTIANA 187 
Summary 
Concluding, the following points may be again emphasized: | 
1. The inheritance of size complexes is so intricate that it is 9 ......% | 
necessary to simplify an experiment upon them in every possible. 
manner. The material used in this investigation, Nicotiana for- okie pou 
getiana Hort. Sand. and N. alata grandiflora Comes, lacks three of “~* all aLianks atuh, . 
the complicating features that usually ensnarl such work. They *-&: 
are almost always naturally self-fertilized, and through numerous 
generations of self-fertilization have become automatically as 
homozygous in their characters as may be expected in Sas 
_reproduce sexually. | Their fecundity is so great that practically 
any quantity of F, individuals can be produced from a single F, 
plant. A plant character was investigated upon which the effect 
of environment is so small as to be negligible, namely corolla size. 
2. These self= species, which are perfectly fertile imier se, 
gave self-sterile progeny. This fact did not affect the production 
of an F, generation, as the F, plants from homozygous parents are 
alike in gametic constitution, and these were perfectly fertile 
inter se. 
3. N. forgetiana with a mean corolla length of 25.6 mm. crossed 
with WN. alata grandiflora with a mean corolla length of 78.8 mm. 
resulted in an intermediate F, generation with a mean variability 
of 44.3 mm. 
4. The variability of the F, generation was very small, being 
about the same as that of the remarkably constant parental species. 
The F, generation, on the contrary, was very variable and both 
grandparental types were reproduced. 
5. It is shown that the F, generation is what would be expected 
if the difference in corolla length shown by these two species were 
represented by the segregation and recombination of four cumu- 
lative but independent pairs of unit factors, dominance being 
absent. 
6. The coincidence of theory and result is as great in this 
case as it is in qualitative characters of like complexity. If the 
Mendelian notation is useful to describe complex qualitative in- 
heritance, it is similarly useful in describing the inheritance of 
quantitative characters. 
