436 RUDOLF BEER [DECEMBER 
the foliar bases will give most instructive illustrations of nuclear 
multiplication unaccompanied by cell-division. In the younger leaf- 
bases each cell contains a single nucleus which is a well-defined, 
generally spherical body that stains very feebly, except the large and 
conspicuous nucleolus, which is its most striking feature. As success- 
ively older sheaths are examined it will be found that the nuclei 
increase in size, the nucleoli keeping pace with the general growth. 
Moreover, the clear, granule-free space, the “ Hof” of Rosen (12 and 
13), which is clearly seen surrounding the nucleolus, becomes broader 
and more noticeable with advancing age. The next stage is that in 
which the nuclei have undergone fragmentation, and several, sometimes 
five or more, nuclei can be seen in one cell. The direct method 
is, however, not the only way in which the plurality of nuclei 
originate within these cells, for I have observed quite a large num- 
ber of cases in which the multinuclear condition was either partly 
or entirely due to karyokinetic division. The mother-nucleus of the 
young cell may undergo karyokinetic division, and by that means give 
rise to several nuclei in one cell, whilst the neighbouring cells may 
attain the same end by nuclear fragmentation. 
Again, within one cell which contains a number of nuclei one 
nucleus may show karyokinetic figures, whilst another is as clearly 
fragmenting. Moreover, out of a group of nuclei, which I have reason 
to think originated by direct division, some may proceed to divide 
further by karyokinesis. These cases are of considerable interest as 
they plainly show that the nuclei, which are in a condition for frag- 
mentation, have by no means necessarily lost their power for active, 
karyokinetic division. 
In the older leaf-bases of Zea Mays direct nuclear division of a 
somewhat different order seems to prevail exclusively. 
In the fragmentation of both the younger and the older nuclei the 
same impulse to divide seems to underlie the process, but the manner 
in which it acts differs in the two cases. 
In order to understand this difference, and since the process in the 
younger cells of Zea Mays does not seem to conform in all respects to 
the usual descriptions of fragmentation, I may perhaps be excused for 
touching on this subject at greater length. In what follows I will 
rely chiefly on the observations which I have made on longitudinal 
sections of the growing-point of the root of Zea Mays, since the steps 
can here be followed with especial clearness. The same observations 
can (with greater difficulty, however) be made on the nuclei of the 
leaf-sheaths. Multinuclear cells occur, but more sparingly distributed 
than in the foliar organs, in the growing point of the root. The 
resting nucleus is a spherical or oval body which stains feebly 
except in the large nucleolus. This nucleolus may in some cases 
attain an enormous size, as for instance. in the cells which are the 
precursors of a vessel, it usually has a perfectly homogeneous appear- 
