OENOTHERA MUTANTS WITH DIMINUTIVE CHROMOSOMES 515 
of a V, formed by contact of the ends of two chromosomes. In 
several cells of each of the three plants the long chromosomes appeared 
to be sufficiently well separated to reveal the small body, had it been 
present, yet it was not found. In such cases it may have been absent, 
hidden by one of the longer chromosomes, or torn out of position by 
the knife in sectioning. Such figures were comparatively rare, how- 
ever, and the large number of cases in which the small body was recog- 
nized in groups of tangled chromosomes where one would expect it 
to be hidden, was one of the sti iking features of these plants. 
3. Origin of the Small Chromosome 
Gates and Miss Thomas occasionally found chromosomes frag- 
menting and degenerating on the heterotypic and homotypic spindles 
of 15-chromosome forms. Sometimes, also, a chromosome of the 
heterotypic group in a 15-chromosome form was seen to be pulling 
irregularly apart in the middle, leaving strands of chromatin matter 
trailing between the separating portions. The same peculiarity was 
observed in a 14-chromosome Lamarckiana-like offspring of a 15-chro- 
mosome plant. The authors believe that this indicated a pathological 
condition of the chromosomes concerned and that probably they would 
have degenerated later. 
The two 14+^-chromosome plants having identical vegetative 
characters (0. aberrans, Nos. 3878 and 4605) had the same type of 
small chromosome, namely, a body which was quite short and even 
more slender, it sometimes appeared, than the long members of the 
group. On the other hand, the 14+^-chromosome O. ruhrinervis had a 
different type of small chromosome — a body which was no longer 
than the small chromosome of the two preceding plants, but which 
seemed to be even broader than the other members of the group, at 
least in some instances. These conditions are particularly interesting, 
in view of the fact that these two mutant types were strongly contrasted 
in so many of their vegetative characters and were about as unlike as 
it is possible for two forms to be. 
The small body of these two types of 14+^-chromosome mutants 
may have arisen in the same or in a different manner. One or both 
may have represented merely a fragment of a degenerating chromosome, 
such as Gates and Miss Thomas observed on heterotypic and homo- 
typic spindles, or a remnant of one of the two halves of a heterotypic 
