OOMYCETES 87 



In still other species, as A. Candida (Davis, 1900; Stevens, 1901; 

 Kriiger, 1910) and A. Lepigoni (Ruhland, 1904), reduction has pro- 

 ceeded a step further. Here already at the differentiation of the 

 protoplasm, a nucleus remains behind in the egg cell (Fig. 53, 5) and then 

 divides, at least in A. Candida, simultaneously with that of the periplasm. 

 One daughter nucleus becomes an egg nucleus, the other degenerates. 

 Ooplasm and periplasm are no longer so distinct as in A . Bliti ; although 

 the coenocentrum is much more highly developed and has become a 

 sharply defined granular mass, rich in food, which can attain fourfold the 

 cross-section of the nucleus; frequently it is also surrounded by a halo 

 of less deeply staining, radial protoplasm. As in the other species of 

 Albugo with only one functional egg nucleus, here also the zygote nucleus 

 divides repeatedly after fertilization, so that the oospore winters over 

 with a large number of nuclei. Except for this peculiarity and the 

 formation of the coenocentrum, the Albuginaceae in A. Candida have 

 attained the stage of Phytophthora. 



As far as is known, in all species, at germination, the oospores swell 

 until the exospore bursts; the content of the endospore bulges out like a 

 sac, bursts and liberates the biflagellate zoospores. 



If the developmental forms of the gametangia of the Peronosporaceae 

 are compared with those of the Leptomitaceae, there appears a continua- 

 tion of the tendency to limit fertilization to only a certain number of 

 nuclei, i.e., to favor some nuclei as sexual nuclei. Thereby, the female 

 gametangia from selection become more strongly developed than the male; 

 as in Araiospora of the Leptomitaceae, the number of functional nuclei 

 falls to one. In the male gametangia, however, again like the Saproleg- 

 niaceae all nuclei remain equivalent; as many of them are used as there 

 are present functional nuclei in the corresponding female gametangia. 



The female gametangia of the Peronosporaceae develop still further. 

 While in the Saprolegniaceae there is a certain natural selection of the 

 (virtual) female gametes, since only a part of the nuclei is used in egg 

 formation, in the Peronosporaceae this differentiation between functional 

 and supernumerary parts extends to the protoplasm and divides it into 

 the gonoplasm (which takes part in egg formation) and periplasm (which 

 has only vegetative duties). This distinction must have arisen so that 

 differentiation ceases after the energids (as in Albugo Bliti) have been 

 differentiated into functional and supernumerary. Thus a differentiation 

 does not extend to the individualization of single functional energids, as 

 in the Saprolegniaceae, but it leaves these unchanged in the center of 

 the female gametangium in the form of a multinucleate egg. For this 

 reason the coenocytic egg of the Peronosporaceae does not correspond 

 to a single egg of the Saprolegniaceae but to the majority of eggs con- 

 tained in an oogonium, just as an egg of the Saprolegniaceae corresponds 

 to several gametes of Olpidium. Caryologically, the difference is not 



