192 THE LOWER FUNGI— PHYCOMYCETES 



identical with that in A. Candida. In A. traqopogonis a multi- 

 nucleate oospherc develops as in A. bliti, but while all the nuclei 

 in the oospherc may be termed potentially sexual, they are not 

 all functional. Following the two divisions in the oogonium, 

 resulting in a multinucleate oospherc, all but one of the nuclei 

 disorganize. The antheridium empties several nuclei into the 

 oosphere, but all but one of these also disorganize. The remain- 

 ing pair of nuclei fuse. The fusion nucleus undergoes repeated 

 divisions at once, the oospore entering the winter in the multi- 

 nucleate condition. The coenocentrum is almost as highly 

 developed as in A. caiidida, but the receptive papilla is relatively 

 inconspicuous. In A. ipomoeae-'panduranae there are apparently 

 a few supernumerary female nuclei which disintegrate in the 

 oosphere, but the fertilization tube discharges only a single male 

 nucleus. Stevens regards the multinucleate condition in A. bliti 

 and A. portulacae as primitive, and the uninucleate condition in 

 A. Candida as a higher development. Arranging the species in 

 a series and passing from A. portulacae at one extreme to A. 

 Candida at the other it will be noted that the coenocentrum 

 increases in height of development and the receptive papilla 

 decreases in size as the number of functional sex nuclei passes 

 from many to one and the epispore changes from reticulate to 

 tuberculate. 



The species enumerated below are the common representatives 

 of the genus in North America. For technical descriptions the 

 papers of Wilson (1907 a; 1908 a) should be consulted. 



A. Candida (Pers.) Kuntze — On many genera and species of the mustard 

 family; probably best known on shepherd's purse (Capsella). 



A. bliti (Biv.) Kuntze — Common on various species of Amaranlhus 

 (pigweed) and on a few related plants. 



A. ijjomoeae-panduranae (Schw.) Swing. — On various Convolvulaceae. 

 The form on Ipomoea batatas has been named A. minor (Speg.) Cif. (Nuovo. 

 (iior. Bot. Ital. n. s. 35: 132, 1928.) 



A. portulacae (DC.) Kuntze — Restricted to the common purslane, 

 Portulaca 'oleracea L. 



A. tragopogonis (DC.) S. F. Gray — Attacking a wide variety of Compositae 

 (common on ragweed, Canada thistle, and salsify). 



Recently Wakefield (1927) has revived the name Cystopus, and 

 applies it to the genus in preference to Albugo. She does this 

 in an attempt to follow the International Rules of Nomenclature 

 (art. 49 bis), which state that, in the case of fungi having a 

 pleomorphic life cycle, only names applied to the perfect stage 



