juiyis, I9IS Rheo Sporangium Aphanidermatus 289 



maturity (PI. XLVI, fig. 18), promptly migrate to opposite sides of the 

 cell, and undergo a second division, from which four nuclei arise (PI. 

 XLVII, fig. 4). Somewhat later a third division gives rise to eight 

 nuclei. This is the greatest number observed in any of the material 

 sectioned, but it is possible that additional divisions occur with the ad- 

 vancing maturity of the oospore. 



The stage shown in Plate XLVII, figure 7, appears to be a reduction 

 division, but it has not been possible to obtain the convincing evidence 

 that would be afforded by chromosome counts. The fused nuclei are 

 larger and differ in shape and in reaction to stain from the nuclei of other 

 stages, while the two that result from the heterotypic division are similar 

 in size and appearance to other nuclei. The interval between the first 

 or heterotypic, and the second, or homotypic, division, while sufficiently 

 long for the nuclei to become fully mature and to migrate to opposite 

 sides of the cell, is relatively brief, so that the binucleate stage is seen 

 much less frequently than the others. 



It would be interesting to follow the history from the 8-nucleate 

 stage of the oospore through germination, but the practical prosecution 

 of such studies can be attempted wisely only after the conditions which 

 induce germination are better worked out. 



TAXONOMY OF THE FUNGUS 



The characters of the fungus discussed in the preceding sections clearly 

 place it in the Saprolegniaceae, but in none of the existing genera of that 

 family. Among the systematic works dealing with the group that by 

 Minden,^ is the most recent. The system employed, which differs in some 

 important respects from those of Schroter^ and Fischer,^ seems well con- 

 ceived and logical and is so constructed as to provide readily a coordinate 

 place for a new genus having the characters of the one to which the fungus 

 under consideration is assigned. It will therefore be used in discussing 

 the relationships of the organism. 



Minden divides the Saprolegniaceae into two sections, according to the 

 method in which the spores are liberated: Section A, in which all the 

 zoospores of a sporangium escape through a common opening, and section 

 B, in which they do not escape through a common opening. Section A, 

 to which belongs the organism being treated, comprises subdivisions 

 with diplanetic and monoplanetic spores. The diplanetic subdivision, 

 with which we are especially concerned, consists of two groups. The 

 first provides for Saprolegnia and Leptolegnia, where the zoospores are 

 distributed for a swarm period immediately on liberation from the sporan- 



' Minden. M. D. von. Pilze. /n Kryptogamenflora der Mark Brandenburg, Bd. s, Heft 3-4. 1911-12. 



2 Engler, Adolf, and Prantl. K. A. E. Die natiirlichen Pflanzenfamilien ... T. i, Abt. i, p. 96. 

 Leipzig. 1897. 



' Rabenhorst, Ludwig. Kryptogamen- Flora Deutschland, Oesterreich und der Schweiz. Aufl. 2, 

 Bd. I, Abt. 4, p. 326. Leipzig, 1892. 



