.Family Cruciferae 187 



per cent, of the crop, although most of it may be 

 prevented. 



Symptoms. Affected plants show a wilting of the 

 foliage in the day, although recovering in the even- 

 ing or during cloudy weather. Diseased plants are 

 dwarfed, pale, and sickly looking. The seat of the 

 trouble is at the roots. The latter swell considerably 

 in size, often taking on the form of a hernia (fig. 30 a). 

 The disease is more severe on seedlings in the seed 

 bed, from whence it is carried to the field. 



The Organism. Club root is caused by a slime mold. 

 The spores of the parasite (fig. 30 b) are nearly round 

 and ^possess a transparent and refractive cell wall. 

 According to Chupp, 1 the first signs of germination 

 are a swelling of the spores, followed later by 

 a bulging at one side. The inner pressure exerted 

 splits the spore wall, thus permitting the protoplasm 

 (swarm spores) to ooze out. The latter is with- 

 out a cell wall (fig. 30 c) , and is capable of motion by 

 means of a thick flagellum at the small end. The 

 germination of the spores is improved 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 host takes place through the wall 

 of the root hair while the organism is in a uninucleate 

 stage. Entrance of the parasite is evidenced by the 

 browning and shriveling of the root hair. The dis- 

 ease does not seem to be spread from place to place 



1 Chupp, Charles, New York (Cornell) Agr. Expt. Sta. Bul. t 

 387:421-452, 1917. 



