Cell Structure, Growth and Division in the Antlieridia of Polytrichum etc. 139 
both have about the same density of stain. Better evidence is furnished 
by triple-stained preparations, in which a rounded, red nucleole is often 
distinguishable from adherent granules of blue chromatin. 
I have also seen nucleoles of the sort described by Beer (1906 a ) and 
Wilson (1909, 1911), which seem to consist of dark particles imbedded 
in a more lightlv-stained matrix. Such nucleoles occiu - in my preparations 
in the outer portions of the sections, where the effects of osmic acid are 
commonly most marked, and where in general the fixation is least satis- 
factory. It seems probable that this appearance is, as Wilson suggests, 
an artifact. The nucleoles shown in Figures 2 and 18 were not of this 
nature, but were uniformly stained; the difference in shading of different 
parts in the drawings is intended to represent the relative distances of 
these parts from the eye of the observer. 
In view of the facts observed, the mass of dark-staining material 
in the central part of the nucleus cannot properly be described as a “chro- 
matin 1111016016 ”; on the contrary, chromatin and nucleolar substance 
seem to be just as distinct throughout the life of the cell as they have been 
shown to be in the cells of higher plants. It is evident from my observa- 
tions that the nuclear structure is not at all like that described and figured 
by the Leeuwen-Reijnvaans (1907 b) for the androgones of Polytrichum-— 
namely, a single large mass filling the greater part of the nuclear cavity, 
which is otherwise empty except for a small granule that separates itself 
at a certain stage from the central mass. Something of the same sort is 
described by the same authors (1908) for the androgonial nuclei of Mnium. 
It is true that in many nuclei there is at some part of the chromatin-linin 
reticulum a knot or granule that is larger than any other intranuclear 
body except'the nucleole (e. g., Figs. 2, 3, 4, 18, upper cell of Fig. 11). In 
the triple stain, such a granule is usually blue or violet; in haematoxylin, 
of course, it is black, like the central mass. If, in the latter case, the 
haematoxylin be sufficiently washed out, this large granule (if present) 
and the central mass are the only nuclear substances retaining the stain. 
It would be easy, from such material, to select a series of cells in which a 
conspicuous granule appears in every possible place between the central 
mass and the nuclear membrane. But if the material be properly stained, 
or even if such a preparation as that just described be carefully studied, 
it is plain that the granule in question retains the stain longer than other 
parts of the nuclear reticulum simply because of its greater size. There 
are always several chromatin knots large enough to be conspicuous in 
properly stained sections; and in many nuclei no one knot or granule 
is noticeably larger than its fellows (e. g., Figs. 7, 8, 13, 14). 
