9 8 



FUNGOUS DISEASES OF PLANTS 



Woronin estimated the losses due to it in the vicinity of St. Peters- 

 burg at $225,000. In the United States it has been disastrous in 

 many of the northeastern states, particularly in those trucking 

 regions which supply the markets of New York and Boston. 



It is, however, occasionally 

 found both South and \Vest. 

 The limits of its distribution 

 have not been clearly defined. 

 Unquestionably it thrives best 

 in a rich, warm, moisture- 

 retaining soil. 



Seedling plants affected by 

 this parasite show a decided 

 ' ' flagging. " They are stunted, 

 unhealthy in appearance, and 

 they may gradually die. Few 

 of those affected when young 

 reach maturity. The parasite 

 attacks the roots and gains 

 entrance to the parenchym- 

 atous tissues. The presence of 

 the organism within the cells 

 affords a stimulus to abnormal 

 growth. There results, in 

 fact, malformities of striking 

 appearance. These vary, on 

 the one hand, from slight 

 nodose swellings in the small 

 rootlets, and knotty masses in 

 the tough roots of some weeds, 

 to the more or less irregular, 

 but generally fusiform, digitate swellings (Fig. 19) in the cabbage, 

 and the lobulated enlargements of the turnip. 



Many members of the mustard family, Cruciferse, are subject 

 to the attacks of this fungus. A complete list of the hosts upon 

 which it has been found cannot be given on account of the fact 

 that much information has been covered up by too general state- 

 ments. In the United States, however, it certainly occurs upon 



Fig. 19. Club Root of Cabbage, pro- 

 duced by Plasmodiophora Brassica^ Wor, 



