108 THE PHYCOMYCETES 



nucleus disintegrate after migration into the periplasm, and this 

 species possesses a small papilla and a large coenocentrum. In 

 A. Candida, typifying the third type, a pair of functional nuclei 

 fuse after disintegration of all supernumerary nuclei, and the size 

 of both papilla and coenocentrum is intermediate between those 

 of the other two types. 



According to Wager (1896), the fusion nucleus soon divides 

 in A. Candida, and after five simultaneous divisions of the nuclei 

 the oospore becomes dormant. Evidence indicates that the first 

 divisions are reductional. Meanwhile a thickened, variously 

 sculptured, three-lavered wall is formed. The oospores of each 

 species appear to have a distinctive pattern of sculpturing, ten of 

 which are illustrated in Wilson's (1907) monograph. After over- 

 wintering, more divisions occur, the wall cracks open, the inner 

 wall slips out as a vesicle containing about 100 zoospores, the 

 vesicle bursts, and the zoospores swim away. 



LITERATURE CITED 



Melhus, I. E., "Experiments on spore germination and infection in certain 

 species of Oomycetes," Wis. Agr. Expt. Sta. Research Bull, 15: 25-91, 



1911. 

 Palm, B. T., "Biological notes on Albugo," Ann. MycoL, 50:421-426, 1932. 

 Stevens, F. L., "The compound oosphere of Albugo bliti,'' Botan. Gaz., 



28: 149-176, 225-245, 1899. 

 "Gametogenesis and fertilization in Albugo," Botan. Gaz., 52:77-98, 157- 



169, 238-261, 1901. 

 ToGASHi, K., Y. SiBASAKi, AND Y. SuGANo, "Morphological studies of white- 

 rust fungi in the cruciferous plants," Agr. Hon., 5: 859-882, 1930. 

 Wager, H., "On the structure and reproduction of Cystopiis candidiis Lev.," 



Ann. Botany, 10: 295-342, 1896. 

 WiANT, J. S., S. S. IvANOFF, AND J. A. Stevenson, "White rust of spinach," 



Phytopathology, 29:616-623, 1939. 

 Wilson, G. W., "Studies in North American Peronosporales. I. The genus 



Albugo," Bidl. Torrey Botan. Club, 34: 61-84, 1907. 



III. "New or noteworthy species," Bidl Torrey Botan. Club, 5S: 361-365, 



1908. 



IV. "Host index," Bull. Torrey Botan. Club, 55:543-554, 1908a. 



PERONOSPORALES 



Approximately 300 species of fungi, commonly called downy 

 mildews, are included in the Peronosporales. All are obligate 



