Cauliflower Diseases 123 



spores) to ooze out. The latter is without a cell 

 wall, and moves by means of a thick flagellum at the 

 small end. The germination of the spores is im- 

 proved by exposing them for a short time to cold and 

 drying. The best medium is water which has been 

 filtered through muck soil. 



Infection of the hosts takes place through the 

 wall of the root hair while the organism is in a uni- 

 nucleate stage. Entrance of the parasite is evi- 

 denced by the browning and shriveling of the root 

 hair. 



Control. If this disease becomes introduced into 

 the greenhouse, the safest course would be to ster- 

 ilize the soil in the benches and in the seed bed. 

 Sterilization with steam or formaldehyde is recom- 

 mended (see pp. 32-43). 



Bacterial Leaf Spot 



Caused by Pseudomonas maculicolum McC. 



Symptoms. The disease is characterized by nu- 

 merous small brownish to purple-gray spots. When 

 the small spots coalesce, the entire leaf surface may 

 be involved. Practically all parts of the leaves are 

 affected. When the midribs and veins are attacked, 

 the tissue becomes shrunken, and the leaves have a 

 puckered appearance. In the early stages of infec- 

 tion, the spots on the leaves are watersoaked, later 

 they become dry and turn dark merging into pur- 

 plish gray. In transmitted light, the centers of the 

 spots are thin, almost colorless, and are surrounded 



