304 MOSSES AND FERNS chap. 



rangiate type. The archegonium neck projects much more than 

 in the other Eusporangiatse, and the vascular bundles in the 

 petiole are truly concentric. The venation of the leaves also 

 becomes that of the typical Ferns. The sporangia are com- 

 pletely free and smaller and more delicate, although truly 

 eusporangiate in development. In all these respects there is an 

 approach to Osminida, unquestionably the lowest of the 

 leptosporangiate series. Helminthostachys too may be almost 

 as well compared to Osmunda as to Angiopteris. 



On the other hand, in the circinate vernation of the leaf as 

 well as the histology, in the roots and in the sporangia, the 

 Marattiacese, especially Angiopteris, approach quite as close or 

 closer to the Osmundacege than does Botrychium or Helmintho- 

 stachys. 



. We may conclude, then, from the data at our disposal, that 

 the living eusporangiate Filicinese consist of a few remnants of 

 widely divergent branches of a common stock, which formerly 

 was predominant, but has been supplanted by more specialised 

 modern types. From this primitive stock have arisen on the 

 one hand the leptosporangiate Ferns, and Cycads, on the other, 

 through Isoetes, or some similar heterosporous forms, the 

 Angiosperms. 



