PTERIDOPHYTES 



147 



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

 is formed. The disorganization of the walls of the mother 



FIG. 127. The ostrich fern ( Onodea striithiopteris), showing differentiation of foliage 

 leaf (a) and sporophyll (6). After MARION SATTERLKE. 



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

 and ready for discharge. 



