SAPROLEGNIALES 163 



has not been possible for workers to apply with certainty the 

 terms monoecious or dioecious, or more correctly the terms 

 homothallic and heterothallic. De Bary's terms dichnous and 

 androgynous have been commonly used. When a single hypha 

 gives rise to both oogonial and antheridial filaments the species 

 is termed androgynous. In such cases antheridia may attach 

 themselves to oogonia from the same or other filaments. If a 

 single main hypha bears filaments of only one sex and those of 

 the other sex come from a distance and seem to arise from other 

 hyphae the species is diclinous. Androgynous species have been 

 assumed to be homothallic and diclinous species heterothaUic. 

 True heterothallism has been demonstrated by Couch (1924 b) 

 in Dictyuchus monosporus and Achlya hisexualis (Coker, 1927: 

 208), and will doubtless be found in other forms. 



The protoplasmic content of the oogonium is at first homo- 

 geneous, but it soon becomes differentiated into denser more or 

 less isodiametric portions separated by intervening avenues of 

 clear cell sap. These naked protoplasmic bodies gradually 

 contract and become spherical in form. They are then termed 

 oospheres. The reserve food supply present in the oosphere 

 exists in the form of globules of fatty material. The aspect of 

 the oosphere when fully formed is one of two types depending 

 upon the position and size of these globules. In all cases the 

 fatty reserve lies near the periphery, but in one type it is in the 

 form of small droplets entirely surrounding the protoplasm, 

 while in the other it is collected into one or a few large drops 

 on one side. In the latter type the oosphere has a one-sided 

 aspect and is termed eccentric. In the former it is called centric, 

 while intermediate types may be termed subcentric. Coker 

 regards this situation as of considerable systematic significance, 

 and says that one type of oosphere is constant in a given species 

 and often throughout a genus. Finally each oosphere secretes 

 a cellulose wall about itself, and is then called an oospore. The 

 oospore at maturity is smooth in most species, but in some is 

 covered with prominent warts or spines. 



As soon as the oospheres are differentiated the antheridia 

 form delicate fertilization tubes which penetrate the wall of the 

 oogonium and branch in its interior, the tip of each branch finally 

 reaching an oosphere and coming into actual contact with it. 

 Earlier writers assumed from the fact of the presence of the 

 fertilization tubes and from analogy with other fungi that actual 



