LEPTO MIT ALES 865 



(Fig. 67 G-H). No cytological details of germination are given. Reduc- 

 tion division presumably occurs at germination, at which time the 

 multinucleate germ tubes are formed. 



In the Rhipidiaceae the sexual process is of a higher type, although 

 the general sequence of nuclear activity is essentially the same as that 

 in Apodachlya. In Sapromyces elongatus (Kevorkian, 1935) the oogonia 

 and the antheridia are formed on different branches and usually on 

 separate thalli. The antheridium contains from four to six nuclei, which 

 are similar to those found in the sporangia and the oogonia. These 

 undergo a single simultaneous mitotic division, after which all but one 

 degenerate. Meanwhile a fertilization tube has been produced which 

 penetrates the wall of the oogonium and reaches the oosphere. One male 

 nucleus is discharged through this tube into the egg. The developing 

 oogonium contains from ten to twelve spherical nuclei, which have been 

 carried into it with the inflowing protoplasm. It is not clear when the 

 basal cross wall is laid down. The contents of the oogonium become 

 vacuolate, however, and the nuclei undergo a single simultaneous mi- 

 totic division. All save one favored nucleus now migrate to the periphery 

 and degenerate. Occasionally degeneration of the supernumerary nuclei 

 may occur without their migration. The gamete nucleus then enlarges 

 and occupies the center of the egg. At some time before fertilization the 

 oogonial contents become differentiated into a large central mass of 

 ooplasm and a thin peripheral layer of periplasm into which the super- 

 numerary nuclei have migrated. The periplasm continues to become 

 less granular than the ooplasm, and a thin membrane eventually sepa- 

 rates the two. Evidently during or prior to the delimitation of the inner 

 periplasmic membrane (the time is not mentioned) the male nucleus is 

 discharged into the ooplasm through the fertilization tube. As in Apo- 

 daehlyabrachynema a. coenocentrum and a few astral rays are developed. 

 Nuclear fusion is delayed, but, from the figures given, it seems to occur 

 before formation of the oospore wall. 



The investigations of King (1903) on Araiospora pulchra and partic- 

 ularly those of Behrens (1931) on Rhipicliwn interruption give the most 

 complete accounts of the cytology of members of the Rhipidiaceae. In 

 R. interruption the oogonium originates in exactly the same fashion as 

 the sporangium, the two structures being indistinguishable at first. About 



