LEPTO MIT ALES 869 



characteristic irregular contour. The irregularities of the oospore wall 

 are not, however, Behrens says, related to the honeycomb-like original 

 disposition of the periplasm, as Minden and others have asserted. That 

 is, the thin primary wall does not form around both periplasm and 

 ooplasm, but originates as an outgrowth from the smooth wall which 

 has been described as lying between the two. During maturation of the 

 oospore the gamete nuclei remain in close proximity and assume equal 

 size (Fig. 68 G). Not even in the fully mature oospore was fusion observ- 

 ed (Fig. 68 H). Judging from this, Behrens supposes that karyogamy 

 occurs shortly before germination. Neither of these two processes was 

 observed, however. 



In Araiospora pulchra the sexual process and the accompanying 

 nuclear phenomena (as described by King, 1903) appear similar to those 

 of Rhipidium interruption, although differences in interpretation are 

 apparent. Cytoplasm and from thirty to thirty-five nuclei migrate into 

 the developing oogonium, which is eventually cut off by a plug from its 

 hypha. The nuclei pass out along radii of the oogonium and become 

 regularly disposed in a peripheral position. The contents at this time are 

 an undifferentiated cytoplasmic meshwork surrounding large irregular 

 vacuoles. As development proceeds, these vacuoles disappear, and the 

 central region becomes more uniformly vacuolate. Near the periphery 

 other regularly placed vacuoles increase in size until the cytoplasm in 

 this region is coarse-meshed. The nuclei, in the interval, have come to 

 rest in the cytoplasmic strands between the vacuoles. In the central 

 region prominent isolated fine-meshed patches appear. King presumes 

 that these eventually fuse to form the coenocentrum, a structure which 

 possibly helps draw the sex nuclei into proximity with one another. 

 Meanwhile differentiation into ooplasm and periplasm has taken place, 

 and at some time a mitotic division of the nuclei has occurred, although 

 the evidence for this is admittedly scanty. The origin of the nucleus of 

 the female gamete was not observed. To judge from the figures given, it 

 is probable that, as in Rhipidium, this nucleus assumes at once a central 

 position in the oogonium. As the ooplasm is cut off from the periplasm, 

 a radial division of the intervacuolar strands of the latter gives rise to a 

 large number of cells. Cell walls are then laid down between adjacent 

 peripheral cells, as well as between these and the central ooplasm. 



