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A TEXTBOOK OF THEORETICAL BOTANY 



pace with the dividing karyosome. Whether this ring is a single unit or 

 whether it is made up of four separate chromosomes has not been finally 

 decided. In the anaphase of the division the two rings become completely 

 separated and the karyosome divides into two, so that in the telophase of 

 the division the chromatin ring of each daughter nucleus again encloses a 

 single kar\'osome. The nuclear membrane now constricts and separates 

 into two to form the membrane around the daughter nuclei. 



SPORE 

 FORMATION 



SPORE 



GERMINATION 



ZOOSPORE 



MEIOSIS 



AKARYOTE 



STAGE 



PLASMODIUM 



GAMETANGIUM 

 FORMATION 



H GAMETANGIUM 



GAMETE 



FUSION 



PLASMODIUM 

 Fig. 190. — Life-cycle oi Plasmodiophora hrassicae. 



Prior to the formation of spores a further change is observable in the 

 behaviour of the nuclei, which is referred to as the akaryote stage. During 

 this stage chromatin is apparently discharged from the nuclei into the 

 cytoplasm, so that both the peripheral chromatin and the karyosome dis- 

 appear and the nuclei can be recognized only as clear areas in the cytoplasm 

 of the Plasmodium. Chromatic discharge at some stage in the life-cycle 

 has been described in other members of the lower Fungi, especially in 

 Synchytrium. The reappearance of chromatin within the nuclei coincides 

 with the prophase of the heterotypic division of meiosis. In these two 

 divisions prior to the formation of spores a typical nuclear spindle appears, 

 and separate chromosomes are apparently formed. No nuclear membrane 

 is present, and it is doubtful if it is reformed between the beginning of the 



