734 THE AMERICAN NATURALIST.  [Vor. XXXIX. 
panied either by a marked enlargement of the nucleus with a 
corresponding increase in the chromatin content or by mitoses 
which distribute to the cytoplasm a greater number of nuclei 
whose sum total of material is very much greater than before. 
Conversely a sudden increase in nuclear material through nuclear 
fusions either sexual or asexual is followed almost immediately 
by general cell growth and increase in the amount of cytoplasm. 
However, such fixed growth relations between nucleus and cyto- 
plasm can hardly be an established physiological law for certain 
highly specialized sperms have an insignificant amount of cyto- 
plasm proportionately to the chromatin that is contained within 
the gamete nucleus. It is evident that the interrelations of the 
nucleus and the cytoplasm are so intimate that the growth activi- 
ties of the one must benefit the other, but that this principle 
can be formulated in definite mathematical ratios seems im- 
probable. : 
The dependence of the nuclei upon favorable situations in the 
cytoplasm is clearly shown in cells when a partial or general 
nuclear degeneration takes place. Thus during the processes of 
oögenesis in the Peronosporales, Saprolegniales, and in Vau- 
cheria there is present a period when the most of the numerous 
nuclei within the oögonia begin to break down and finally 
become disorganized. The causes of the nuclear degeneration 
are not entirely clear but apparently the organ is unable to 
supply all of the nuclei in their respective situations in the cyto- 
plasm with the conditions necessary. for their life. There is con- 
sequently a sort of struggle for existence among these numerous 
nuclei and only those that are favorably placed in the cell are 
able to survive. In all forms the surviving nuclei occupy a situ- 
ation in the center of the masses of protoplasm which are to 
become the eggs and those that break down are at or near the 
periphery of the cell. In several genera (e. g., Albugo, Perono- 
spora, Pythium, Sclerospora, Saprolegnia, and Achlya) the sur- 
viving nuclei seem to owe their good fortune to a very close 
association with the cytoplasmic structure termed the caenocen- 
trum. The coenocentrum is a clearly differentiated region of 
the cytoplasm and is probably the morphological expression of a | 
dynamic center in the eggs of these fungi. Stevens’ ('99, : OI) 
