ore highly
organised plants only in cells which have lost their specific
functions. Such cells are no longer capable of specific reproduction. An
interesting case in this connection is afforded by the internodal cells
of the Characeae, which possess only vegetative functions. These cells
grow vigorously and their cytoplasm increases, their growth being
accompanied by a correspondingly direct multiplication of the nuclei.
They serve chiefly to nourish the plant, but, unlike the other
cells, they are incapable of producing any offspring. This is a very
instructive case, because it clearly shows that the nuclei are not only
carriers of hereditary characters, but that they also play a definite
part in the metabolism of the protoplasts.

Attention was drawn to the fact that during the reducing division of
nuclei which contain chromosomes of unequal size, gemini are constantly
produced by the pairing of chromosomes of the same size. This led to
the conclusion that the pairing chromosomes are homologous, and that one
comes from the father, the other from the mother. (First stated by T.H.
Montgomery in 1901 and by W.S. Sutton in 1902.) This evidently applies
also to the pairing of chromosomes in those reduction-divisions in
which differences in size do not enable us to distinguish the individual
chromosomes. In this case also each pair would be formed by two
homologous chromosomes, the one of paternal, the other of maternal
origin. When the separation of these chromosomes and their distribution
to both daughter-nuclei occur a chromosome of each kind is provided for
each of these nuclei. It would seem that the components of each pair
might pass to either pole of the nuclear spindle, so that the paternal
and maternal chromosomes would be distributed in varying proportion
between the daughter-nuclei; and it is not impossible that one
daughter-nucleus might occasionally contain paternal chromosomes only
and its sister-nucleus exclusively maternal chromosomes.

The fact that in nuclei containing chromosomes of various sizes, the
chromosomes which pair together in reduction-division are always of
equal size, constitutes a further and more important proof of their
qualitative difference. This is supported also by ingenious experiments
which led to an unequal distribution of chromosomes in the products of
division of a sea-urchin's egg, with the result that a difference was
induced in their further development. (Demonstrated by Th. Bo