864 AQUATIC PHYCOMYCETES 



The well-coordinated movement of these swarmers through the water 

 seems, however, to indicate that there is some central controlling body, 

 most likely the main body of the nucleus, of which the granules are, 

 after all, an integral part. 



It is in the sexual stage that the most interesting nuclear phenomena 

 are to be found. Since members of the two families differ somewhat 

 from each other in this phase they will be considered separately. 



In the Leptomitaceae sexuality is known in Apodachlya and Apodach- 

 lyella. Only Apodachlya brachynema, however, has been investigated 

 cytologically. In this species (Kevorkian, 1935) the oogonium is terminal 

 and the antheridium is the hyphal segment immediately below it (Fig. 

 67 A, p. 862). The male organ at maturity contains from three to four 

 spherical nuclei which are scattered in the protoplasm. These undergo 

 a simultaneous mitotic division, after which one nucleus enlarges and 

 the remainder degenerate. Meanwhile a simple pore has been formed 

 on the membrane separating the two gametangia, through which the 

 contents pass into the oogonium. No specialized fertilization tube is 

 produced. The developing oogonium possesses at first from ten to 

 twenty nuclei, which have been carried into it by the inflow of proto- 

 plasm prior to the formation of the basal septum separating it from the 

 antheridial cell. These nuclei are at first more or less evenly distributed 

 in the protoplasm. When the oogonium achieves its maximum size and 

 is separated from the antheridium a single simultaneous mitotic division 

 of these nuclei occurs. This division is coincidental with that in the 

 antheridium (Fig. 67 B). The nuclei of the two organs may not, however, 

 all be at the same stage of division. All but one of the nuclei in the 

 oogonium make their way, possibly by means of vacuolar activity, to 

 the periphery of the oosphere. The single favored nucleus assumes a 

 central position and enlarges, attaining ultimately from two to three 

 times its original size (2.5-3.5 \i in diameter). The peripheral nuclei then 

 degenerate (Fig. 67 C). A poorly defined irregular coenocentrum sur- 

 rounds the egg nucleus. The male nucleus, upon its entrance into the 

 oogonium by way of the pore, migrates toward the nucleus of the egg 

 (Fig. 67 D) and makes contact with it. Both then enlarge. A few astral 

 rays emanate from the region of the nuclei. Actual fusion, however, may 

 not take place until the oospore wall is in the process of thickening 



