OENOTHERA MUTANTS WITH DIMINUTIVE CHROMOSOMES 51 I 
''The left-hand group contains 7)^ chromosomes, while the 
right-hand group consists of 6 whole chromosomes, a half-chromosome 
and a small fragment. There is in addition a chromosome in the 
cytoplasm near this group, which has been left out of the nucleus in 
interkinesis. This makes the full quota of 15 chromosomes. The 
origin of the fragment is obscure, but the figure shows that even frag- 
ments of chromosomes may be distributed occasionally to the daughter- 
nuclei. Unless afterwards extruded from the pollen nuclei, such frag- 
ments will no doubt affect the later development of the individual ; 
they might remain independent or become attached to or fused with 
one of the other chromosomes." 
Thus the researches of Geerts have shown that during the female, 
as well as male, reduction in certain 21 -chromosome forms, chromo- 
somes in excess of 14 may fragment and degenerate, while the researches 
of Gates and Miss Thomas have demonstrated that one of the chro- 
mosomes of certain 15-chromosome forms may fragment and de- 
generate during the reduction divisions of the pollen mother cell. 
These facts, together with other evidence which will be offered by the 
writer later, suggest the conclusion that chromosome degeneration 
occurs in all forms having 14-^ -chromosomes, though probably less fre- 
quently in plants having 28, than in other 14-}- -chromosome forms par- 
ticularly if the 28 represent a double set of the original 14. In other 
words, there appears to he a tendency in i4-\- -chromosome forms, to return 
to the original 14-chromosome condition; furthermore, this tendency 
appears to he more pronounced in forms having 21 chromosomes, than in 
those having a double set of the original 14. It may be that sometimes 
a portion, sometimes all, of the chromosomes in excess of 14 degen- 
erate, and that gametes of 1 4 -f -chromosome plants are equipped with 
various irregular numbers of chromosomes.^ In addition to the whole 
7 or 7 -f -chromosomes present in the germ-cells of such forms, we may 
expect to find, occasionally, one or more fragments of chromosomes. 
2. 14+^-chromosome offspring of 0. lata X 0. Lamarckiana 
A 14+^-chromosome condition has been observed by the writer in 
3 plants. The first, No. 3878, was found among the Fi offspring of 
0. lata X 0. Lamarckiana grown at Cold Spring Harbor in 1908 and 
the second, No. 4605, in another culture of the same cross in 1909. 
^ Doubtless more frequently true of 21-, than of 15- and 28-chromosome forms. 
