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1903] OOGENESIS IN SAPROLEGNIA 341 



the nuclei often in mitosis move from the center of the oogonium 

 to the periphery. He suggests **that the nuclei pass to the 

 periphery to rid themselves of superfluous kinoplasm, possibly to 

 prevent parthenogenetic development of the oosphcre." This 

 theory seems to the writer to suppose an order of events and 

 degree of preformed specialization more intricate than the evi- 

 dence warrants. It seems more likely that "zonation" repre- 

 sents an event that happens to accompany, but is secondary to, 

 those processes which gather the ooplasm in the centef of the 

 oogonium and give the ^^^ its coenocentrum and characteristic 

 alveolar structure. 



Indeed, the conditions that cause that extraordinary degene- 

 ration of nuclei in the oogonium must furnish in large part the 

 solutions of these problems. This phenomenon is universal, 

 whether the nuclei break down in the eggs themselves (Sapro- 

 legniales), or are relegated to such secondary sexual structures 

 as periplasm (Peronosporales) or a conjugating tube, as in the 

 ascomycete Pyronema. As we have seen in Saprolegnia, the 

 many nuclei in the eggs during advanced stages of oogenesis 

 are all much reduced in size, and the only thing that saves the 

 fortunate survivors of the general severe conditions is proximity 

 to that center of metabolic activity, the coenocentrum. There 

 is a limit to the number of nuclei possible in a given amount of 

 cytoplasm. The nutrition of the oogonium decreases as oogene- 

 sis proceeds, and finally reaches a point when the nuclei are 

 sorely pressed to maintain themselves. This certainly seems to 

 be the history for the Saprolegniales, and probably every phy- 

 comycete w^hose sexual organs are coenogametes, as these struc- 

 tures are generally formed late in ontogeny, when the period of 

 vegetation is about completed. 



The nuclei are then subjected to a keen struggle for existence, 

 and, in spite of the fact that they are in a symplast, which is 

 itself a unit, they may well be supposed each to look after its 

 own Interest as far as possible. The outcome of that struggle 

 is largely determined by the activities of the cytoplasm which 

 may develop such metabolic centers (morphologically expressed 

 by coenocentra) that certain nuclei by good fortune of favorable 



