868 AQUATIC PHYCOMYCETES 



of the oogonium, is cut off from its branch by a cellulin plug (Fig. 68 

 D, p. 866). It contains about four nuclei. The oogonial wall at the point 

 of application of the antheridium bulges out, papilla-like, possibly be- 

 cause of the slighter resistance of the wall at this point to the internal 

 pressure of the oogonium. This protuberance then springs into a corres- 

 pondingly formed cavity of the antheridium. Thus the antheridium and 

 the oogonium are brought into intimate contact. Because of the con- 

 stancy of point of application of the antheridium to the oogonium, 

 Behrens raises the question as to whether or not the female structure 

 emits material attractive to the antheridial branch. The four antheridial 

 nuclei are like those of the oogonium, but stain more intensely. Soon 

 after mitosis has occurred in the oogonium they too undergo a single 

 mitotic division. Only one of the eight nuclei thus formed persists; the 

 remainder degenerate. Soon after this nuclear division the wall of the 

 oogonium dissolves at the point of application of the antheridium, and 

 the antheridium produces a fertilization tube (Fig. 68 E). At the time 

 of entrance of the fertilization tube into the ooplasm there occurs a 

 progressive resorption of the periplasm and an increase in the amount 

 of the deep-staining peripheral ooplasmic material. A delicate membrane 

 is laid down between the vacuolated periplasm with its supernumerary 

 nuclei and the ooplasm. The egg nucleus at this time is as yet unfused 

 with the male nucleus. It possesses a perceptible beak with centrosome- 

 like granules at the tip (Fig. 68 E). Delicate polar rays which extend 

 beyond a darker-stained coenocentrum are clearly visible. Upon the 

 dissolution of the tip of the fertilization tube a single male nucleus is 

 discharged, and this apparently moves fairly quickly to the vicinity of 

 the somewhat larger egg nucleus (Fig. 68 F). The tenuous membrane 

 delimiting the periplasm now becomes continuous, completely separates 

 the ooplasm from the dwindling periplasm, and gradually thickens and 

 becomes doubly contoured, the accretion evidently being derived from 

 the previously mentioned deeper-stained outer layer of the ooplasm. 

 As the wall thickens, this outer layer slowly decreases. The double 

 contour of the wall is visible even before the rays have vanished from 

 the female nucleus. The residue of periplasm and the supernumerary 

 nuclei then disappear. At the same time the oospore wall thickens and 

 assumes by unequal accretions, aided no doubt by outside material, its 



