5i8 
ANNE M. LUTZ 
they studied. Furthermore, if we regard the appearance of these 
unstained regions in somatic chromosomes merely as a stage preceding 
fragmentation, then we should find numerous instances of fragmenta- 
tion in groups of somatic chromosomes, but we do not. 
While the plant in which Gates and Miss Thomas found somatic 
chromosomes with clear areas chanced to be a 15-chromosome mutant, 
it should not be inferred that this peculiarity is characteristic 
of 15-chromosome forms only, nor even of 14+ -chromosome forms 
only. It is not associated with the 14 -{--chromosome condition in 
Oenothera, /of these chromosomes are just as common in 14-chromosome 
O. Lamarckiana and other 14-chromosome forms as in 14-^ -chromosome 
individuals. I have found plants (mutants and hybrids) in the 
Lamarckiana group with the following soniatic chromosome numbers; 
14, I4+^ 15, 16, 18, 19, 21, 22, 23, 24, 26, 28, 29 and 30 — the number 
being constant, so far as ascertained, for each type and for each in- 
dividual of the type — and have observed these chromosomes with 
clear spaces in every type studied. It was found that this peculiarity 
was no more common in hybrids and in mutants than in 0. Lamarcki- 
ana, nor more common in 14-f-- than in 14-chromosome forms. 
Since each of the three 14+^-chromosome plants had a 15-chromo- 
some mother (9 0. lata X cf 0. Lamarckiana) it is probable that the 
small chromosome was derived from the mother, and that each in- 
dividual was the product of 9 + 7. However, Gates and Miss 
Thomas found that the extra chromosome of 15-chromosome forms 
degenerated only occasionally; furthermore, since they found chro- 
mosomes pulling apart in the middle and sometimes ''fragmenting 
into three parts " in 14- as well as in 15-chromosome plants, it is conceiv- 
able that 0. lata X 0. Lamarckiana might produce a 14+^-chromosome 
offspring by means of a 9 8 -f cf6+^ union. If the small body of de 
Vries's ruhrinervis was merely a piece which had become detached from 
one of the ordinary chromosomes, then it may have been derived either 
from the 15-chromosome mother or the 14-chromosome father (9 7+^ + 
7 or 9 7 + 7+0 • The small body may have been derived from 
the 14-chromosome parent by still another means. Since the hetero- 
typic chromosomes of 0. Lamarckiana are occasionally distributed in 
groups of 6 and 8, it is quite possible that one of the members of the 
8-chromosome group sometimes fragments and degenerates just as it 
does at times in the 8-chromosome groups of 15-chromosome forms. 
