MYXOMVCETES. SLIME MOLDS 99 



varieties of cabbage, cauliflower and Brussels sprouts (Brassica 

 oleracca), turnip (Brassica campestris), rutabaga (Brassica Rapa), 

 radishes (RapJianns sativa), and certain mustards (Sinapis and 

 Brassica). It has also been found upon such weeds as shepherd's 

 purse (Caps el la Bursa-pastoris} and hedge mustard (Sisymbrium 

 officinalc). In Europe besides most of the plants mentioned Mat hi- 



FIG. 20. A CROSS SECTION OF CABBAGE ROOT AFFECTED BY THE CLUB 

 ROOT FUNGUS. (Invaded cells enlarged and phloem tissue multiplied) 



ola incana and Iberis umbellata are hosts. There seems to be little 

 recent data of interest bearing upon the comparative susceptibility 

 of different varieties of cultivated plants. Many mistakes have 

 doubtless been made in assigning to this fungus injuries appear- 

 ing upon other orders of host plants, and sometimes even those 

 upon crucifers, due to nematode worms. It is often difficult to 

 distinguish between the two causes of disease. 



