FIG. 10. SilpMum integrifolium. Longitudinal sections of microsporangia ; x 520. 

 /(, single row of archesporial cells ; in two cells division into primary sporogenous 

 and primary parietal cells has already taken place. B, sporogenous and tapetal cells 

 sharply differentiated. 7, later stage showing spore mother-cells in synapsis. Z>, 

 a tetrad (only three microspores shown) formed within the spore mother-cell. After 



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35 



