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1909] GRIGGS—MITOSIS IN SYNCHYFRIUM 349 
fertilization and reduction would be well-nigh meaningless. For its 
_ support it has had, besides the constancy of the chromosomes in the 
species, various observations on nuclei which were known to contain 
either more or less than the normal number of chromosomes. 
The great difficulty in the way of the theory has always been that 
the chromosomes apparently lose their individual existence during 
the vegetative phases of the nucleus. In many cases where the nuclei 
are rapidly dividing the chromosomes do not, however, entirely lose 
their individuality between the successive divisions, but divide and 
reproduce themselves directly from the compact condition of mitosis. 
These cases have been the evidence by which the vegetative period 
of the nucleus was bridged over by the individuality hypothesis, for 
there is an unbroken series of intergradations from this condition to 
that in which the chromosomes have completely lost their morpho- 
logical identity, and one would not suppose that nuclei in one condi- 
tion differed fundamentally from those in the other. Accordingly, 
basing their statements on observations of nuclei in which the indi- 
vidual chromosomes could be traced, with more or less certainty, 
from mitosis to mitosis, several writers have asserted confidently that 
the individuality of the chromosomes is maintained through all con- 
ditions of the chromatin, whether visible or not. 
But the transformations of a set of chromosomes which, after 
they are once formed, persist and divide are not necessarily equivalent 
to the formation of a new set from a diffuse reticulum. If the chro- 
matin reticulum gave rise only to the chromosomes, the analogy might 
be closer; but when, as frequently happens, large amounts of chro- 
matin are cast out into the cytoplasm as nucleoli, microsomes, or in 
Mass, it is evident that the succeeding differentiation of the chromo- 
somes involves factors different from those entering into the mere 
transformation of a chromosome which persists intact through what- 
ver metamorphoses it may pass. This may be illustrated perhaps 
y comparing the chromosomes to metal rods which remain distinct 
from each other when cold, but as the temperature approaches the 
melting point become soft, lose their shape, and partially fuse together, 
though each retains its distinctness and can be reclaimed unchanged 
°n cooling. But after they have once melted together, all this is 
changed, and they can be regained from the homogeneous flux only by 
