PLANT DISEASES 



377 



receive their necessary supply of water, and so wilt 

 and die. The bean blight is another important bacterial 

 disease. 



381. Club Root of Cabbage. — This disease, also known 

 as " club foot," has long been a serious menace to the cab- 

 bage industry in Europe. The 

 estimated damage in Russia alone 

 for a year is over $5,000,000. 

 The disease is likewise found in 

 almost all regions in the United 

 States where cabbages are grown 

 extensively. Young plants are 

 stunted and many die at this 

 stage ; others continue to live but 

 never form a head that is market- 

 able. The roots are stimulated 

 to excessive growth, and swell- 

 ings (Fig. 211) are caused; these 

 swellings are often only slight 

 enlargements on the sides of the 

 roots, but in other cases they 

 reach a considerable size. The 

 parasite, which is usually consid- 

 ered to be one of the slime molds, 

 is known to attack the cabbage, 

 turnip, cauliflower, radish, ruta- 

 baga, and Brussels sprouts, and 

 has been found on the mustards 

 and other weeds. The thick-walled spores of the fungus 

 live through the winter in the soil and in diseased tissues. 

 In the spring the spores germinate and infection takes place 

 in the roots of young plants. No means has yet been dis- 

 covered for the control of this disease, but rotation of crops 

 and care in planting only healthy individuals may consider- 

 ably check the loss. 



Fig. 211. — The club root 

 of cabbage. The younger roots 

 and the lower portions of the 

 stem become greatly swollen; 

 the plants are weakened and 

 often killed. 



