FIFTEEN- AND SIXTEEN-CHROMOSOME OENOTHERA MUTANTS 1 01 
a diverse progeny of dwarfs, not a single individual of which resembled 
the mother. While it appears that we are entitled to regard this form 
as inconstant, Professor Bartlett, in discussing this question by letter 
says, "The fact must not be overlooked, however, that this particular 
individual of Oe. pratincola mut gigas belonged to a mass mutating 
strain." 
Gates ('15a, pp. 189-190) described the meiotic distributions of 
the chromosomes of a 22-chromosome offspring of O. gigas X 0. lata 
rubricalyx, presumably resulting from a 9 i^-i-r^ S union. Here he 
found that ''the arrangement in the heterotypic telophase i - disiirc tly 
not into two equal groups of 11 each, but usually (and apparently with 
much regularity) into 10 and 12." In addition to these, 9-, 11-, and 
13-chromosome groups were observed and certain other irregularities 
of distribution, but these were apparently uncommon. ''Hence," he 
says, "we conclude that a considerable number of the pollen grains will 
contain only nine chromosomes, although the majority will probably 
contain 10, 11, or 12." 
The behavior of O. lata has shown us that although male reduction 
in a plant may form daughter groups containing different numbers 
of chromosomes, it does not necessarily follow that more than one type 
of pollen grain, capable of functioning, will be produced. Thus, Gates 
and Miss Thomas ('14) have shown that male reduction in 0. lata 
usually results in 7-8 distributions of chromosomes, yet there is much 
to indicate, as we have seen, that only 7-chromosome pollen grains, 
capable of functioning, are produced by this form. Hence the ap- 
pearance of 9-, 10-, II- and i2-chromosome groups at various stages 
of the male reduction process in the 22-chromosome hybrid does not 
assure us that more than one type, or that any type of pollen grain, 
capable of functioning, was produced by this form.^^ Gates Ci^a, 
p. 213) studied a sample of pollen from this hybrid containing 281 
grains and found that 11.4 percent of the grains were "good." It is 
quite possible that all but one type of grain were eliminated and that 
only one type of female gamete, capable of functioning in union with 
45 The 22-chromosome offspring of 0. lata X 0. gigas sometimes produce small 
quantities of pollen containing about the same percentage of seemingly good grains 
as the pollen from Gates's hybrid. I have repeatedly attempted to self these plants, 
but in every instance have failed to secure a single seed. These results may have 
been brought about by incompatibility of fertilization combinations, or it may be 
that the "seemingly good" grains were just as incapable of functioning as the 
shriveled and distorted ores. 
