43 6 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 Zca 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 Zca 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 Zca 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- 



