340 



THALLOPHYTES 



Club Root of Cabbage. 1 This is a disease of Cabbage caused 

 by a parasitic Myxomycete. The Myxomycete gains entrance 

 through the roots and lives upon the cells of the plant. The 

 presence of the parasite causes the wart-like developments on the 

 roots and stem of the Cabbage, and so injures the plant that 

 no head is produced and even death often results (Figure 292). 



Within the cells of the 

 Cabbage the plasmodia live 

 and form spores (Figure 

 293). When liberated 

 through the decay of the 

 Cabbage, the spores are 

 carried by water, animals, 

 or wind to other plants. 

 The spores may lie in the 

 ground and infect plants in 

 succeeding years. This dis- 

 ease is not only destructive 

 to Cabbage but often at- 

 tacks Turnips, Radishes, 

 Rutabagas, and Cauli- 

 flower. The important fea- 

 ture in controlling the 

 disease consists in prevent- 

 ing the spores from functioning by burning infected plants, 

 treating the soil with lime or sulphur, and rotation of 

 crops. 



Powdery scab of the Irish Potato. 2 This disease is caused by 

 one or more kinds of Myxomycetes which enter the tubers and 

 roots of the Irish Potato and destroy the tissues (Fig. 294). The 

 Amoeba-like plasmodia live in the cells, which, due to the presence 



1 Cabbage Club Root in Virginia. Bulletin 191, Virginia Agr. Exp. Sta., 

 1911. 



Studies on Club Root. Bulletin 175, Vermont Agr. Exp. Sta., 1913. 

 Studies on Clubroot of Cruciferous Plants. Bulletin 387, Cornell Uni- 

 versity Agr. Exp. Sta., 1917. 



2 Powdery Scab (Spongospora subterranea) of Potatoes. Bulletin 82, 

 U. S. Dept. Agr., 1914. 



Powdery Scab of Potatoes. Bulletin 227, Maine Agr. Exp. Sta., 1914. 

 Spongospora subterranea and Phoma tuberosa on the Irish Potato, Vol. 7, 

 No. 5, pp. 213-254, Jour. Agr. Research, U. S. Dept. Agr., 1916. 



FIG. 293. Cross section of a root 

 of Cabbage affected with Club Root, 

 showing the plasmodia (p) within the 

 tissues. From Woronin. 



