Chromosomes in Pollen Mother-cells. 
34i 
in those cases in which a continuous spirem is present in the daughter 
nuclei ( Podophyllum , Lilinm ), but the sister segments unite end to end 
in this spirem. 
The doctrine of the individuality of the chromosomes requires the 
assumption that the reduced number contains all the qualities of the species, 
else how is it possible to explain the fact that the monoecious prothallium 
of a homosporous fern, which arises from a spore containing only one-half 
the sporophytic chromosomes, produces by the union of gametes a sporo- 
phyte identical with the parent sporophyte ? The same applies to cases of 
true parthenogenesis. The fact that the eggs of such a fern do not develop 
into sporophytes without the union with sperms would seem to be due 
merely to the lack of quantity of chromatin rather than to the absence 
of any quality. The assumption that the chromatin of each spore contains 
all the necessary characters of the species seems quite essential. Yet, 
on the other hand, the reducing division cannot be qualitative unless some 
of the chromosomes contain pangens that are either not possessed by 
others at all, or, if possessed by all, then certain pangens must contain 
qualities in a greater degree of potentiality. Since any two individuals 
of the same species have many more qualities in common than those that 
are different, it follows that the chromatin would consist chiefly of pangens 
representing these common qualities, while the comparatively few characters 
of difference would be represented by a relatively small number of pangens. 
Moreover, the pangens representing these relatively few characters would 
not only be different from the rest, but their affinity for any of the numerous 
pangens might diminish as the qualitative difference became greater. It is 
also conceivable that the pangens which represent certain special or widely 
different qualities may have a stronger affinity for some of the more 
numerous pangens than for others, and in this way there could be brought 
about a localization of the special pangens. Consequently, in the phylo- 
genetic development of the race a more permanent association might result 
between certain groups of pangens and those bearing the special qualities. 
In some such manner certain chromosomes might have become qualitatively 
different from others. The pangens representing these most markedly 
different qualities may be conceived as coming together in one chromo- 
some, or as distributed among different chromosomes. The foregoing 
may be made clearer by an illustration. The greatest structural and 
functional differences between any two sexually differentiated individuals, 
or members of an individual, of the same species is probably that of sex ; 
and it is possible that the pangens representing sex are those that differ 
most from all others. This difference may be conceived as being so great 
that such pangens may unite to form a distinct chromosome, or sex- 
differential, as seems possible in the case of certain insects. However, 
the pangens representing these special characteristics, whether they pertain 
