I'TERIDOPHYTES 



147 



numerous mother cells, in each of which a tetrad of spores 

 is formed. The disorganization of the walls of the mother 



k 



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1 



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Fig. 137. The ostricli fern ( Onoclea strvthioptei^), showing differentiation of foliage 

 leaf (a) and sporophyll (ij.— After Marion Satteelee. 



cells sets the spores free in the cavity of the sporangium, 

 and ready for discharge. 



