Family Cruciferae 205 



The black rot, Pseudomonas campestris, is the same 

 as that of the cabbage, p. 190, and the white rust, 

 Cystopus candidus, is the same as that of the mus- 

 tard, p. 211. 



ROOT ROT 



Caused by Thielavia basicola (B. and Br.) Zopf. 



Root rot of horseradish is of little economic im- 

 portance. The disease is confined to the roots of the 

 plant. In advanced stages the normal root system 

 may be entirely lacking, leaving a charred, blackened 

 stub. New roots are constantly formed above the 

 diseased area, but these in turn become affected 

 and die. It is these new roots which the plant 

 attempts to produce that manage to keep the 

 infected host alive in a stunted and useless form. 

 For a description of the organism and methods of 

 control, see p. 275. 



ASCOCHYTA LEAF SPOT 

 Caused by Ascochyta armor aci<R Fckl. 



This form of leaf spot is rather scarce in the United 

 States and may be easily overlooked. The disease 

 is manifested as brownish leaf spots of various sizes. 

 Within the spots numerous pycnidia are formed 

 which bear numerous elliptic-oblong, hyaline one- 

 septate spores. 



