565 
Constituents of the Cell, 
but in the divisions of the sporogenous cells to form the 
definitive spore-mother-cells, he found nucleolar substance 
much more abundant, and its occurrence in the cytoplasm 
correspondingly common. The material of Psilotum at my 
disposal, from the Botanic Garden at Bonn, showed only 
the spore-formation from the definitive mother-cells, which 
accounts for my having failed to agree in all respects with 
Guignard’s observations. The fact that in Osmunda the 
definitive mother-cells are formed in autumn, has prevented 
the study of the divisions preceding their formation, my 
material having been collected in early spring. But if the 
extranuclear nucleoli are sometimes common in certain cells, 
this does not alter the fact that they are extremely rare in 
others, or lessen the force of the evidence against the view 
which regards the nucleolus as a permanent organ. Guignard 
does not seem to have sufficiently emphasized this point. 
It is hardly necessary to repeat what was pointed out 
in my preliminary paper, that the great variability and 
evident passivity of the nucleoli are equally opposed to the 
conception of their definiteness and permanence. Their in- 
constant form, the readiness with which they break up or 
fuse together, and their tendency to assume the globular form 
when unhampered and not too large, all point unmistakably 
to the probability that they are of a fluid consistency, while 
their gradual disappearance in the early stages of division, 
as the karyokinetic forces come into full activity, and their 
equally gradual reappearance as this activity is ceasing, show 
plainly that they are directly acted upon by those forces. 
The constant occurrence of nucleoli in the nuclei of most 
widely different plants indicates the importance to the cell 
of the material which takes this form during its less active 
condition. Very careful studies of preparations from a large 
number of plants, stained with the best reagents for nucleolar 
substance, have quite failed to show me any change in the 
staining properties of the more permanent cell-constituents, 
which would give an indication of the distribution of the 
material of the dissolved nucleoli, although some writers have 
