FUNGOID DISEASES OK CRL-ClKKKS loi 



3. Apply nitrate of soda, as a top-dressing. 



4. Frequent horse-hoeing even in the late sum- 

 mer has in many cases been found beneficial. 



IV. White Rust {Albugo Candida. Kuntz. ; ( 'v- 

 stopus candidiis, Pers.). Class : Phvcomncktk.i-: ; 

 Order : Pkronosporalks. 



This fungus attacks various cruciferous plants, 

 but is especially abundant on shepherd's purs(; 

 {Capsella bursa pastoris) where it appears as a 

 lime-white coverino" causino^ deformitv of the stems, 

 leaves, and leaf-stalks. 



The mycelium grows within the host ; later it 

 bursts through the surface, 

 forming spores (in chains) 

 (Fig. 30) which constitute the 

 white powder. These spores 

 are carried by the wind, and 

 in the presence of moisture 

 give rise to zoospores which 

 swim for a time, and on 

 coming to rest, form a germ 

 tube which can enter a cru- 

 ciferous plant. Resting 

 spores are formed as a re- 

 sult of sexual union, in most plants, but not in 

 shepherd's purse. 



V. Blackening of Rape. — Rape in particular 

 suffers from the attack of Sporidesniiuui cxdiosuui, 

 which forms blackish-brown spots, especially on the 



Fig. 30. — White rust {Cysto- 

 piis candidits). Portion of 

 the hypha with conidio- 

 phores ; (</) bearing the 

 con i d i a (i ) in chains. 

 (Magnified.) 



