FIFTEEN- AND SIXTEEN-CHROMOSOME OENOTHERA MUTANTS 95 
than is apparent, for two gametes having the same number of chro- 
mosomes, or nearly so, may be represented by entirely different chro- 
mosomal combinations. Yet Gates's assertion that "it is at present 
unknown whether the number alone determines the viability, or 
whether particular chromosome combinations will, owmg to incom- 
patibility, fail to produce an embryo afte- fertilizadon " voices a 
quesiion which is still unanswered, if we believe that each of the 
14-chromosome mutant types produced directly by 0. Lamarckiana 
is represented by a chromosomal combination differing from that of 
the parent, then in crossing these various types one would expect to 
find some of the 7+7 combinations resulting less compatible than 
that of O. Lamarckiana, selfed. All 14-chromosome forms which have 
been tested by the writer have been found to produce an abundance 
of seed when selfed or crossed wdth other 14-chromosome forms; further- 
more, relatively larger percentages of these seeds (compared with those 
derived from forms having more than 14, but fewer than 28, chromo- 
somes) were found to be capable of germinating. No evidences of 
incompatibility have been observed thus far; indeed fertility appears 
to be associated with the 14-chromosome condition wherever found. 
Ordinarily only a small percentage of the few seeds derived from 
vselfed 2 1 -chromosome forms are capable of germinating in the few 
months commonly allowed them in seed pans. De Vries ('09, Vol. I, 
p. 261) has shown that Lamarckiana seeds may lie in the ground for 
two or more years before germinating, and the writer has recently 
verified these results. If so many 14-chromosome seeds may germinate 
late one may be led to inquire whether certain 14 +-chromosome 
seeds may not be even more inclined to germinate tardily. In the 
opinion of the writer, the lower percentage of germination commonly 
exhibited by seeds of most 14 +-chromosome forms is due to the total 
inability of many 14 +-chromosome seeds to germinate, rather than 
to a greatly increased tendency on the part of these seeds to germinate 
late. It is furthermore probable that, ordinarily, a larger percentage 
of the products of selfed 14+-, than of selfed 14-chromosome forms are 
merely seed-like structures, and therefore incapable of germinating. 
Particularly is this probably true of the products of selfed triploid 
individuals, for one frequently finds that a large percentage of the few 
seeds obtained are small, flat and unpromising appearing. 
Regarding the relative percentages of 14-, 15- and i6-chromosome 
offspring derived from selfed 15-chromosome forms, it is possible that 
