328 



FORMS OF FILICALES 



particularly the structure of the annulus are important charac- 

 teristics to be observed in identifying the ferns. In the flowering 

 ferns, Osmunda, the large shght-stalked sporangia are pro- 

 vided with a rudimentary annulus of a few thickened cells lo- 

 cated at one side of the capsule (Fig. 224, A). The entire leaf 

 or certain leaflets are completely covered with the sporangia, 

 little more than the vascular bundles remaining (Fig. 225, A). 



Fig. 225. Common forms of the Filicales: A, the fiowering fern, Os- 

 munda, showing below two green leaflets and above two sporangia-bearing 

 leaflets. At left a cluster of sporangia magnified. The first leaves in the 

 spring only bear sporangia; those appearing later have only green leaves. 

 B, chain fern, Woodwardia. C, Christmas fern, Polystichum. D, bladder 

 fern, Filix. E, hay-scented fern, Dennstaedtia — s, sorus enlarged. F, Woodsia 

 — After Sprague. 



Osmunda belongs to the lowest group of the Filicales and shows 

 certain analogies in the arrangement and structure of its collateral 

 vascular bundles with the Ophioglossales. The majority of 

 ferns in temperate climates are characterized by sporangia of 

 the type shown in Fig. 224, B, and they are distinguished by 

 the form and arrangement of the sori and indusia. The shield 

 fern, Dryopteris, has a rather circular or curved sorus covered 



