142 
R. A. HARPER 
retention we should have a factor which would tend to such an ori- 
entation of the cleavage planes as in the end would produce uninucle- 
ated spore units. The chemical changes in the colloids in such acid 
regions might lead even to the visible differentiation of the hyaline 
zones which in the later stages of cleavage in Fuligo and the spore 
embryos of Pilobolus seem to predetermine the planes of the cleavage 
furrows. 
Hofmeister has emphasized the possibility of widely different 
chemical processes and conditions coexisting in a polyphase colloidal 
system like the cell because of the low mutual diffusion rates of its 
various elements and the possibility of such differences in reaction 
between the nuclear region and the cytoplasmic region of the cell must 
be recognized. If we add to this conception of the nucleus as a center 
of water retention the further conception, suggested by its relation to 
cell plate formation in the higher plants and the ascus, that it is a center 
for the production of plasma membrane materials, we have two 
factors which would work in harmony to bring about the process of 
progressive cleavage as described, since the diffusion outward from the 
nucleus of substances to be used in forming the plasma membrane 
would again tend to cause the cleavage planes to pass midway between 
any given pair of nuclei. 
INDEX TO LITERATURE 
1. Bally, W. Die Chytridineen im Lichte der neueren Kernforschung Mycolog. 
Centralbl. 2: 289. 1913. 
2. Bally, W. Cytologische Studien an Chytridineen. Jahrb. wiss. Bot. 50: 95. 
1911. 
3. Barrett, J. T. Development and sexuality in some species of Olpidiopsis (Cornu). 
Fischer. Ann. Bot. 26: 209. 1912. 
4. Barrett, J. T. The development of Blastocladia strangulata, n. sp. Bot. Gaz. 
54: 353- 1912. 
5. Baum, Joh. Pet. Zelltheilung in Pilzhyphen. Diss. Fulda. 1900. 
6. Conard, H. S. Spore formation in Lycogala exiguum Morg. Iowa Acad. Sci. 
17: 83. 1910. 
7. Davis, B. M. Oogenesis in Saprolegnia. Bot. Gaz. 35: 233. 1903. 
8. Davis, B. M. Spore formation in Derbesia. Ann. Bot. 22: i. 1908. 
9. De Bary, A. Morph. u. Physiol, der Pilze, Flechten u. Myxomyceten. 1866. 
10. Debski, B. Beobachtungen iiber Kernteilung bei Chara fragilis. Jahrb. wiss. 
Bot. 30: 227. 
11. Fanner, J. B. and Williams, J. L. Contributions to our knowledge of the 
Fucaceae, their life-history and cytology. Trans. Roy. Soc. Lond. Ser. B.' 
190: 623. 1898. 
