5^3 
Constituents of the Cell. 
directly from each other, and seeks to establish the principle, 
‘ Omnis nucleolus e nucleolol as of equal value with the long- 
accepted statement of Flemming, 4 Omnis nucleus e nucleol 
This is directly contrary to the generally prevailing view, 
that the nucleoli consist of a reserve substance which is 
ordinarily dissolved or otherwise changed during the earlier 
stages of karyokinesis, so that they are no longer recognizable 
as nucleoli. 
The results of my earlier studies upon this question, begun 
soon after the appearance of Zimmermann’s paper, have 
already (’94) been briefly stated. More recently Guignard 
(’94) and Strasburger (’95) have discussed the question. And 
a somewhat fuller account of its present status seems not to 
be superfluous, especially since Guignard seems to take a less 
definite position than is warranted by the facts he admits. 
The fate of the nucleoli during karyokinesis has, very 
naturally, been discussed by almost every writer on that 
process, since those bodies are so conspicuous when present. 
And the number of observed cases of their persistence during 
the spindle-stages or of their occurrence in the cytoplasm had 
been so small before the publication of Zimmermann’s results 
that they had been practically ignored. The fundamental 
significance attached to them by this author led to a renewed 
investigation of the facts. In my examination of spore- or 
pollen-mother-cells of Osmunda regalis and O. cinnatnomea , 
Psilotum triquetrum , Ceratozamia longifolia , and Convallaria 
majalis , the first divisions in the spores of Pellia epiphylla , 
root-tips of Vicia Faba , Hyacinthus sp., and Allium Cepa , and 
the wall-layer from the embryo-sac of Leucojum aestivum , 
I have found only in rare cases a trace of nucleoli during 
the middle stages of karyokinesis, or of any in the cytoplasm 
at any stage. Reference to the figures accompanying my 
earlier paper and the present one will show what has been 
found to be the general condition of these bodies during the 
chief phases of nuclear division. Figs. 2 to 6 on the plate 
given herewith show several steps in the first division of the 
spore-mother-cell in Osmunda regalis , while Figs, it and 12 
