32 



MYCETOZOA AND RELATED ORGANISMS 



Fig. 7. Plasmodiophorales. Life cycle of Plasmodiophora brassicae Wor. (After Cook 

 and Schwartz: Trans. Roy. Soc. London, B, 218:283-314.) 



formed. The zoospore possesses two anterior flagella, as demonstrated by 

 Ledingham (1934), the longer one pointing forward, the shorter directed 

 almost at right angles. Ellison (1945) showed that both of these flagella 

 are of the truncated whiplash type, neither showing any tinsel structures. 

 This is a character that indicates that Plasmodiophora is not related to 

 the Olpidiopsidaceae, whose anteriorly biflagellate zoospores possess one 

 flagellum of each of these two types. The zoospore is more or less amoe- 

 boid. When it comes into contact with a root hair or epidermal cell of the 

 root of a suitable host, the flagella disappear and a hole is dissolved in the 

 host cell wall through which the amoeba enters, then this hole is closed, 

 presumably by host action. Cook and Schwartz (1930) showed that within 

 the root hair this amoeba enlarges and mitotic divisions of the nucleus 

 occur until a small Plasmodium is formed, containing from a few up to 

 one hundred nuclei according to Fedorintschik (1935). This Plasmodium 

 cleaves into uninucleate cells around each of which a thin wall is formed. 

 Whether this wall contains cellulose or chitin has not been determined. 

 They give rise to structures called sporangia or gametangia. The nucleus 

 divides mitotically two or three times and thus there are formed four to 

 eight uninucleate, anteriorly flagellate swarm cells, smaller than those 

 that emerge from the resting spores. The number and character of the 



