58 



THE LOWER FUNGI— PHYCOMYCETES 



of Plasmodiophora, states that the niyxamoebae never migrate 

 through the host cell walls into adjacent cells, later workers 

 (Lutman, 1913: 3; Chupp, 1917: 435; Kunkel, 1918:570) find that 

 the organism spreads widely through the tissue by direct migra- 

 tion. Consequently, as Kunkel points out, many thousands 

 of separate " Krankheitsherde" may result from a single primary 

 infection. In fact, Kunkel states that the typical large club 

 is the result of a single infection. 



In the early stages of its intracellular existence the parasite 

 does not interfere sufficiently with the functioning of the host 

 cell to prevent its normal nuclear and cell division. Later, 



Fig. 4.- — Plasmodiophora brassicae Woronin. (a) Formation of spores. (6) 

 Mature spores. {After Chupp 1917; fig. 102.) 



the host protoplasm is largely absorbed, and the myxamoebae 

 increase in size until they practically fill the cell. This brings 

 them into direct contact and they are said by some workers to 

 be completely merged. Others state that their identity is never 

 lost, and that nuclear divisions are simultaneous only in a given 

 myxamoeba, not throughout the whole mass. In any case, 

 the host cell is finally almost or completely filled with the proto- 

 plasm of the parasite. The two nuclear divisions which are 

 believed to constitute reduction occur, and the spores are cut out 

 about the resultant nuclei (Fig. 4, a). They are more or less 

 spherical and are provided with definite smooth membranes. 

 Although the spores do not break apart simultaneously they lie 



