CHYTRIDIALES 



57 



received in consequence various common names such as clubroot, 

 and fingers and toes. The diseased roots are usually greatly 

 enlarged locally, the swellings or galls varying in size and shape. 

 On cabbage especially they are 

 typically large and fusiform. 



The organism gains entrance 

 into the roots from the soil 

 through root hairs or other epi- 

 dermal cells. Inoculation exper- 

 iments performed by Kunkel 

 (1918: pZ. 61) show that infection 

 may occur also through the epi- 

 dermal cells of the stem below 

 ground. The organism enters 

 as a uninucleate amoeboid zoo- 

 spore (myxamoeba). In the 

 host cell it increases in size, 

 becomes multinucleate (Fig. 3, 

 a) , and fragments into a number 

 of daughter myxamoebae (Fig. 3, 

 b). When the host cell divides 

 several of these myxamoebae are usually incorporated in each 

 of the daughter cells. Other cell divisions follow and soon a 

 group of infected cells exists. These httle clusters of diseased 



Fig. 2. — Planmodiophora brassicac 

 Woronin. Spores and swarmspores. 

 {After Chupp 1917; fig. 97.) 



Fig. 3.—Plasmodiophora brassicae Woronin. (a) Multinucleate myxamoeba 

 in base of root hair of oabbage. (6) Root hair containing a number of daughter 

 myxamoebae resulting from division of the primary myxamoeba. {After Chupp 

 1917; fio. 104.) 



cells resulting from primary infection by a single zoospore were 

 termed by Woronin " Krankheitsherde." Although Nawaschin 

 (1899), who first used modern cytological methods in the study 



