﻿19031 OOGENESIS IN SAPROLEGNIA 523 



Bliti^ A. Porttilacae^ and A, Tragopogofiis really act as a whole, 

 and it is hardly possible to separate in these forms the coenoga- 

 metes (oospheres) from the gametangia. When we «^ay that 

 the oogonium of Albugo, Peronospora, Sclerospora, and Pythium 

 acts as a whole, we mean that the periplasm is not to be consid- 

 ered as waste material, but as a specialized region of the cell, 

 with important functions in relation to the eggs, which it helps 

 to protect by assisting in the formation of heavy walls. The 

 Mucorales, Pyronema, and these three species of Albugo furnish 

 the best known illustrations of coenogametes. 



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ORIGIN AND EVOLUTION OF THE COENOGA.METE. 



There seem to be only two possible sources of the coenoga- 

 mete. It is conceivable that a uninucleate sexual element might 

 become multinucleate, perhaps through such an increase in the 

 protoplasmic content that more than one nucleus would be 

 required to control satisfactorily its activities. The second possi- 

 bility is an origin from a multinucleate gametangium that has 

 given up the production of uninucleate gametes, and acting as a 

 unit becomes itself a sexual organ, a coenogamete. Such an 

 evolutionary process would find its analogy in those sporangia 

 (conidia) of certain species of Pythium and Peronospora, w^hich 

 now^ germinate as a whole (by a tube) instead of forming zoo- 

 spores. 



The first possibility has absolutely no evidence in its support. 

 There is no series of forms whose sexual cells pass from a uni- 

 nucleate condition to a multinucleate. There are no indications 

 that such an evolutionary process has ever taken place among 

 plants. There are only two instances known where eggs, free 

 from periplasm, are multinucleate. The eggs of Albugo are so 

 intimately associated with periplasm that they cannot be consid- 

 ered apart from the gametangium in which they lie. These two 

 examples are the binucleate and trinucleate eggs of the Sapro- 

 legniales and the multinucleate eggs of Sphaeroplea anmilina 

 Braiinii, Our investigations of Saprolegnia have shown that the 

 processes of oogenesis in that group have as an end the sacrifice 

 rather than the preservation of nuclei, and the uninucleate con- 

 dition is evidently the goal of evolution. Klebahn's (1899) and 



