1909] GRIGGS—MITOSIS IN SYNCHYTRIUM 353 
somes. In these nuclei the small karyosomes number 4, 5, 6, 7. 
The respective nuclei must therefore have 16, 20, 24, 28 chromosomes, 
and still have no more than four! 
There seems to be no option but to conclude that in Synchytrium 
there is no morphological continuity of the individual chromosomes, 
nor is there any definite set of chromatin granules of whatever size 
which are passed on intact from nucleus-to nucleus. The number of 
chromosomes seems to be a physiological rather than a morphological 
constant. Not the chromosome but the nucleus itself seems to be 
the morphological unit of the lowest order. Apparently any mass of 
chromatin that is capable of organizing a nucleus at all, i.e., any 
particle of nuclear matter that is able to continue life and reproduce 
itself, whether it originally contained portions of all of the chromo- 
somes or of only one of them, will preserve the characteristic number 
of chromosomes along with the other hereditary characters of the 
species. “ 
Although such a hypothesis seems to be required to explain the 
phenomena of nuclear division in Synchytrium, it would not be wise 
to attempt to reach any decision as to its general applicability at. this 
time. In proposing it to account for these features of Synchytrium, 
the writer is not at all oblivious of the enormous amount of evidence 
which has been heaped up in recent years in support of the individu- 
ality of the chromosomes. The occurrence of protochromosomes in 
the nuclei of many cells (OVERTON 14); the persistence of super- 
numerary chromosomes in cases of polyspermy, etc.; and the remark- 
able size and shape differences among the individual chromosomes 
such as have been discovered in animals, notably by McCiunc and 
Montcomery, and recently in plants by SCHAFFNER (15) and Miss 
Hype (9), along with many other observations of a similar nature, 
are facts which give very great weight to the hypothesis of the indi- 
Viduality of the chromosomes. Nevertheless, it must be remembered 
that almost all of the evidence in favor of the individuality hypothesis 
is of Suggestive rather than demonstrative value. This was clearly 
recognized by all observers until about five years ago, but since that 
ime the amount of such evidence has increased to such an extent that 
Cytologists have been much less cautious than before in using the 
hypothesis. The renaissance of MENDEL’s law so favored the general 
