188 



THE LOWER FUNGI— PHYCOMYCETES 



here treated first, since a position between the Pythiaceae and 

 Peronosporaceae would fail completely to indicate the natural 

 relationships. 



The members of the family are all embraced in the single 

 genus Albugo. 



1. Albugo (Persoon) Gray (1821: 540). 

 syn. Cystopus Lev. (1847: 371). 



About twenty-five species have been described in this genus 

 for the world. Wilson (1907 a; 1908 a) in his monograph of North 

 American forms includes fifteen. Several of these are common 



Fig. 69. — (a) Albugo portulacac (DC.) Kuntze, showing sporangiophores and 

 chains of sporangia, (b-f) A. Candida (Pers.) Kuntze. (6) Swarmspores. (c) 

 Young oogonium and antheridium. (d) Mature oospore in oogonium, (e-/) 

 Germinating oospore, (gf) A. tragopogonis (DC.) Gray; mature oospore, {g, 

 after Schwarze 1917; others after de Bary 1887.) 



and almost cosmopolitan in distribution. The species may be 

 separated into two groups on the basis of the character of the 

 markings of the outer wall of the oospore (Fig. 69). Some 

 {e.g., A. Candida, A. ipomoeae-panduranae) have a definitely 

 tuberculate epispore, while in others {e.g., A. bliti, A. tragopogonis, 

 A. portulacae) it is reticulate. Cytological studies have demon- 

 strated that differences in life-histories are correlated with this 

 difference in epispore markings, the group characterized by the 

 tuberculate epispore containing the more highly developed 

 species. This fact will be clearly indicated in the following 

 discussion of the sexual process. 



