86 WEATHERWAX: GAMETOGENESIS IN ZEA Mays 
results of the reciprocal crosses were not due to a failure of the 
sperm to fuse with the polar nuclei, as Webber had suggested 
(25, pp. 34-37) in explanation of a similar occurrence. Therefore, 
they were forced to conclude that two applications of the one 
factor may dominate one application of the other. 
Results leading to the same conclusions have since been se- 
cured with color combinations. If a plant heterozygous for 
purple aleurone be selfed, four types of endosperm should be 
produced, depending upon the number of times the factor combi- 
nation for purple is present. And when such an experiment is 
made, there are produced, besides the proper number of white 
seeds, visibly different types of purples, appearing in significant 
ratios. Emerson (8) has recently given a detailed report on a 
number of experiments of this kind. 
It may be said, therefore, that the solution proposed by Cor- 
rens was a valid one, although it did not apply to the problem that 
he had in hand. By taking advantage of the triple parentage of 
the endosperm, this series of experiments provided the first direct 
evidence of the cumulative effect of repeated applications of the 
same factor, which is the basis of the multiple factor hypothesis. 
But these theoretical conclusions have all been based upon 
the assumption of certain cytological facts not hitherto demon- 
strated. If, in the formation of the maize embryo sac, all four 
megaspores functioned, which the writer (24, p. 492) at one time 
thought probable, the two polar nuclei, coming respectively from 
the two nuclei resulting from the heterotypic division, would be 
genetically different in a hybrid plant. Therefore, a sweet-starchy 
hybrid, crossed with pure sweet, should produce all starchy seeds, 
since the two polar nuclei together would represent an entity 
unaffected by segregation and always carrying the dominant factor. 
But, as a matter of fact, when a cross of this kind is made,ai:!I 
ratio is produced. The assumption that only one megaspore 
survived had good precedent in Koernicke’s work (15) on Triticum, 
recently verified by Jensen (13); but now it is definitely known that 
the same is true of maize. 
_ In some crosses of white varieties with purple or red, a mottled 
aleurone is produced; and in sweet-strachy crosses a few seeds 
have been found with the endosperm bilaterally divided—one 
