292 



PLANT MORPHOLOGY 



fungus. The development of the antheridium is characteristic. The 

 inner portion of the embryo forms the stem and foot, the outer portion the 

 leaf and root. The Filicales are a highly organized group. Their prin- 



FiG 247. Stages in development of the embryo of a polypodiaceous fern, X225. A, 

 two-celled stage; B, four-celled stage; C, slightly later stage; D, embryo showing differentia- 

 tion of organs. 



cipal advance over the eusporangiate ferns lies in the development of their 

 spore-producing structures. 



5. Hydropteridales 



The Hydropteridales include 2 families, 5 genera, and nearly 90 species. 

 The two families are probably of separate origin and their inclusion in the 

 same order is largely a matter of convenience. Both are more advanced 

 than any of the families of Filicales, however, and in the same ways. All 



