PTERIDOPHYTA 



261 



stele was either circular in outline (Botryopteridaceae) or more or less 

 lobed (Zygopteridaceae). In the most primitive members division of the 

 frond was not limited to one plane and the leaf stalk bore a series of 

 bifurcating branches (Fig. 216). In some cases the differentiation 

 between stem and leaf was imperfect in that no blade was formed. 



Fig. 216. Reconstruction of the leaf of Etapteris lacattei; fertile portion above and sterile 

 portion below; one-quarter natural size. (After Hirmer.) 



The Coenopteridales were eusporangiate and homosporous. The spo- 

 rangia were large and either terminal or marginal on the ultimate divisions 

 of the frond. Sometimes the sporangia were united to form a synangium- 

 like structure. The output of spores was large. The sporangium wall 

 was more than one layer of cells thick. Dehiscence took place by a ter- 

 minal pore or a longitudinal slit; in the latter case a rudimentary annulus 

 was present. 



2. Ophioglossales 



The Ophioglossales comprise 3 genera and about 80 species. Ophio- 

 glossum and Botrychium, each with about the same number of species, are 



