Family Chcnopodiaceae 121 



portance in localities where potatoes sujffer heavily 

 from the disease. 



Symptoms. The S3niiptoms of the disease on beets 

 (fig. 20 b) do not differ much from those of the Irish 

 potato (see p. 317)- Occasionally, the scabs which 

 arise before the beet is full grown disappear entirely, 

 leaving merely a small scar. This is somewhat 

 sunken and has a definite outHne. In normal 

 cases of infection, the scabby areas on the beet are 

 greater in area, and thicker ; the corky layer of the 

 spots decidedly bulging out. Immediately below the 

 scabby areas the tissue is a discolored reddish brown. 



The Organism. The cause of beet scab is the same 

 as that of the scab of the white potato (see p. 317). 

 The parasite is a soil organism, and thrives best under 

 allfflli conditions. 



Control. Beets should not grow where Irish po- 

 tatoes, carrots, or radish are known to suffer from the 

 same, disease. Lime and fertilizers which tend to 

 make the soil alkaline should be avoided. 



Root Tumor 



Caused by Vrophlyctis leproides (P. Mag.) Trab. 



This trouble fortunately is as yet unimportant in 

 the United States. The disease is characterized by 

 the formation of nodules or outgrowths often the size 

 of a walnut on the rootlets or leaves. The fleshy 

 root itself is seldom attacked. The tissue of the 

 tumors contains numerous cysts or spore-bearing 

 cells. 



