326 BOTANICAL GAZETTE [May 
because the products of the segmentation all remain in the same 
nucleus and are propagated in each mitosis. 
There is, therefore, no satisfactory cytological evidence that the 
chromosomes are composed of smaller units whose equal division 
and distribution is brought about in each mitosis. ‘According to 
the most careful cytological studies, we cannot with any assurance 
affirm the existence of smaller differential units composing the 
chromosomes. On the other hand, the many lines of evidence 
indicating the more or less independent behavior and genetic con- 
tinuity of the chromosomes within a nucleus from mitosis to mitosis 
in the vast majority of cases, seems clear and incontrovertible. 
To the writer, this independence of behavior will find an explana-_ 
tion in some difference, probably of a chemical nature, between 
the materials of which the individual chromosomes are composed. 
That this is insufficient, however, as an entire explanation, 
seems to be shown by the case of Oenothera gigas (GATES 6). This 
mutant has 28 chromosomes, double the number found in its 
parent, O. Lamarckiana. As stated in the above-mentioned paper, 
O. gigas probably contains merely a duplicate set of O. Lamarcki- 
ana chromosomes, although other changes seem to have occurred 
simultaneously in producing the mutation. The new number of 
chromosomes persists, however, and this shows that even though 
certain of the chromosomes are as much alike as two chloroplasts, 
yet, having occurred in a given nucleus, they will reappear in its 
descendants. This may be accounted for by the fact that the 
mitotic mechanism brings about a simultaneous division of all 
the chromosomes present. But it does not account for the further 
fact that all these bodies reappear in the prophase of each mitosis, 
and hence must have maintained their identity in some way while n 
the alveolated and distributed condition of the resting nucleus. 
The lines of evidence which favor this conception of chromo 
some continuity from mitosis to mitosis are too numerous to ent 
merate, and since this view in some form is now widely accepted by 
cytologists, an enumeration is unnecessary in the present conne™ 
tion. One clear result showing the unity in behavior-of the chro- 
mosomes was found in the hybrid O. lataXO. gigas (5). This 
hybrid had 21 chromosomes, 7 derived from the O. Jate egg and 
