CHYTRIDIALES 51 



Nothing identical with this type of division has been seen in 

 any other group of organisms, though in some of the most primi- 

 tive Protozoa (order Lobosa) it is said to be approximated. 

 Several workers have justified their inclusion of doubtful species 

 in the Plasmodiophoraceae on the single point of their possession 

 of this type of division. Before the two reducing divisions 

 occur a stage exists in the cycle in which the stainable chromatin 

 of each nucleus is extruded into the cytoplasm. This is termed 

 the "akaryote" stage. The two mitoses which immediately 

 follow are typical, and result in a tetrad of nuclei. According 

 to Cook (1928 b) these nuclei become in some cases the centers 

 of spores, while in others the primary nucleus of the spore is 

 diploid and reduction occurs in zoospore formation. During 

 the cruciform division the nucleolus divides and persists in the 

 daughter nuclei. Since the dividing nucleolus is drawn out 

 into a dumb-bell shape, and hes at right angles to the chromatin 

 gathered at the equatorial plate, the division figure as viewed 

 from the side has the aspect of a cross. The essential feature 

 of this mitosis is thus the persistence and division of the nucleolus. 

 In the reduction divisions the nucleolus disappears, as in most 

 higher plants, and is re-formed de nova in the daughter nuclei. 

 A nuclear fusion (karyogamy) may occur at some point in the 

 cycle, but, though reported in one or two cases, cannot be said 

 to have been satisfactorily demonstrated. Several workers 

 have expressed the opinion that it will be found in the pairing 

 of zoospore-like gametes when germinations are obtained in 

 satisfactory quantity. The whole nuclear situation is well 

 summarized in the recent papers of Cook (1926; 1928 h) on 

 Ligniera. Just how much significance should be attached to 

 the cruciform division is perhaps in question, and conclusions 

 concerning the taxonomic position of the group based on this 

 feature alone would seem premature in the light of our ignorance 

 of nuclear division in various lower groups. The spores have 

 been observed to germinate in but few species of the family 

 and by but few investigators. In Plasmodiophora, according 

 to Woronin (1878) and Chupp (1917) the spore wall cracks open 

 and the protoplast emerges as a single zoospore which swims 

 for a time with a single cilium attached at the forward end. The 

 posterior end of the zoospore is figured by Woronin as amoeboid. 

 If the zoospores could be shown to be of this type throughout 

 the group, a character indicating relationship of this family 



