PHYCOMYCETES 1 49 



X. WHITE "RUST" OF CRUCIFERS 

 Cystopus candidus (Pers.) LeV. 



Davis, B. M. The Fertilization of Albugo Candida. Bot. Gaz. 29: 296-310. 



pi. 22. 1900. 

 Wager, H. On the Structure and Reproduction of Cystopus candidus Lev. 



Ann. Bot. 10: 295-339. pis. 23, 26. 1895. 

 Zalewski, A. Zur Kenntniss der Gattung Cystopus Lev. Bot. Centrbl. 15 : 



215-224. 1883. 



Fig. 49. Flowers and Peduncles of Radish deformed by Cystopus 

 (Photograph by II. H. Whetzel) 



The common white "rust" of cruciferous plants appears to 

 be common throughout the world. The fungus is frequently 

 one of the first of the order to make its appearance in the spring 

 and the last to disappear in winter. Evidently, it is not readily 

 affected by minor climatic differences, and probably slight dews 

 are sufficient to insure its propagation. 



This fungus is most common upon the forms of the ubiqui- 

 tous shepherd's purse (Capsella Bursa-pastoris) ; but it is also 

 common upon the radish (Raphanus sativus), horse radish 

 (Cochlearia Armoracia), cress (Brassica oleracea), turnip (Bras- 

 sica Rapa), mustard {Brassica nigra), water cress (Radicula Nas- 

 turtium-aquatic um), etc. 



