Notes . 
375 
opinion concerning their nature; namely, that they are globules of 
a more or less fluid substance which is passively subject to the forces 
active in the cell. The karyokinetic forces appear to cause the 
solution or emulsion of the nucleolar substance, which then again 
separates out in drops when these forces cease to be active. Such 
bodies can certainly not be regarded as definite organs of the cell ; 
and it is upon the assumption that they are such that the views of both 
writers above quoted rest. 
Furthermore, the study of spore-mother-cells of Psiloium and 
Osmunda has enabled me to detect, in favourably-cut microtome 
sections, the presence of the true centrospheres, corresponding to 
those described and figured by Guignard. These bodies, which 
Karsten has clearly overlooked, take no marked stain and are far 
less easy to recognize than the smallest globules of nucleolar sub- 
stance. That they are to be regarded as true organs of the cell, 
‘ kinetic centres/ there seems little doubt. My observations also 
throw some light on the interesting and still unsettled question of 
their origin. In several cases I have found them lying outside of the 
nucleus, though close to it, while the nuclear membrane was appar- 
ently still quite intact. Indeed, in all the plants studied they seem to 
be of cytoplasmic rather than of nuclear origin. 
It seems also extremely probable that the granules observed by 
Farmer 1 in the pollen-mother-cells of Lilium Martagon are similar 
nucleolar masses to those seen by other writers ; but it is equally 
improbable that they are ‘ regular and normal constituents of the cell 
during these stages of division.’ 
Incidentally my studies appear to throw some light on the nature 
of the body termed, ten years ago, by Strasburger, the ‘paranucleolus/ 
and called by Zimmermann the ‘ sickle-stage ’ of the nucleolus. This 
crescent-shaped body is found at one margin of the nucleus, and has 
been supposed to represent a stage in the disappearance of the nucle- 
olus. I have observed it chiefly in tissues of considerable thickness, 
and most strikingly in the pollen-sacs of Ceratozamia. Here, in 
material fixed with alcohol, almost every nucleus may show one of 
these bodies, and always on the side turned away from the nearest 
surface of the organ. The fixing fluid proposed by Mann often fixes 
Ceratozamia material better than alcohol, and then one finds very few 
1 Annals of Botany, Vol. VII, p. 392 ; Sept. 1893. 
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