STEVENS: KINOPLASM AND NUCLEOLUS. 83 
daughter nuclei. I find it possible to get some direct evidence on 
this point. The nucleoli of the mother cells vary in size within 
quite narrow limits, and are fairly perfect spheres. It is, therefore, 
an easv matter to determine their volume with a fair degree of ac- 
curacy. I find the volume of an average nucleolus of the mother 
cells to be 265 cubic microns, while the sum of the volumes of the 
nucleoli of the daughter nuclei is about ;', of this amount. Ac- 
cordingly about ,*, of the substance of the nucleolus of the mother 
cell has been employed in some manner, and the most reasonable 
inference is that the new structures which have been formed during 
the division of the mother cell have been the recipients of this 
material. The new structures are, of course, the kinoplasmic 
spindle and the cell plate. It is imperative that these structures 
should be provided for before nuclear division sets in, since at that 
time the energies of the cell are probably greatly taxed by the pro- 
cesses of mitosis. The very large amount of nucleolar substance 
in the mother cells and the greatly diminished amount at the time 
of the completion of the daughter cells are facts which speak 
strongly for the nutritive function of the nucleolus. 
The severance of the spindle fibres from the daughter nuclei 
before the completion of the cell plate is a fact which deserves 
special consideration. Haberlandt, after referring to observations 
by Treub and Strasburger which showed the attempt of nuclei dur- 
ing cell division to keep in close connection with the forming cell 
plate, comes to the following conclusion: ‘‘Da liegt nun die 
Annahme nahe, dass ausschliesslich in den Verbindungstaden der 
Einfluss der beiden Tochterkerne fortgepflanzt werde und desshalb 
bloss innerhalb dieses Fadencomplexes zur Bildung der Zellplatte, 
resp. der Scheidewand fiihre.”’!| The behavior of the pollen mother 
cells of Asclepias shows, however, that kinoplasmic connection 
with the nucleus is not always necessary to the formation of the 
cell plate, and that if the daughter nuclei exert an influence on the 
formation of the plate it is through the medium of the cytoplasm. 
The persistence with which the nucleus remains attached to the 
kinoplasmic plasma membrane of forming ascospores may have the 
significance of establishing a direct highway for the transfer of 
nucleolar material to the growing membrane, but it seems to me 
that the formative influence of the nucleus is also transmitted in 
this way. The formation of a plasma membrane about an ascospore 
and the laying down of the cell plate in a dividing cell are in some 
respects quite different problems. In the former case there are no 
boundaries already existing which shall determine the form and 
11. c., pp: 110-112. 
