4 Osmundaceae 



or dictyostelicf, departure of leaf-traces in all but 

 haplostelic forms making definite leaf-gap in the stele. 

 Sporangia on the undersides or on the edges of ordinary 

 foliage leaves, or of modified leaves {sporophylls) with 

 reduced laminae ; in the latter case the sporophylls are 

 not aggregated on special shoots, or special regions of 

 the shoot. Spermatozoids multiciliate. 



Order i. Filicales. Sporangia mostly arising from 

 single cells, more rarely from groups or from several 

 layers of cells, usually in definite aggregates {sori\ 

 Prothallus not subterranean, generally flat. 



Suborder i. FiLlciNEAE. Wall of the sporangium 

 typically with a prominent cell row or cell group 

 iannubLs) concerned with the dehiscence of the spor- 

 angium. Spores all alike producing comparatively large 

 free-living monoclinous or diclinous prothalli. 



SiMPLlCES (Bower). Sporangia grouped in sori each 

 containing few sporangia of simultaneous origin on a 

 flat or nearly flat receptacle or spread over the lower 

 surface of the fertile leaf, relatively large, sessile or 

 subsessile, with a large spore output. Annulns trans- 

 verse or oblique or (as in the British genus) represented 

 by a group of thickened cells. Indiisium typically 

 absent. 



Family OSMUNDACEAE. Stem upright covered with 

 the bases of spirally arranged leaves. Stele with con- 

 tinuous mantle of peripheral phloem and anastomosing 

 xylem strands surrounding a pith, Petiolar vascular 



t Dictyostele. A stele in which the hollow cylinder of the 

 solenostelic type is interrupted by leaf-gaps which overlap 

 (Brebner, I.e.). 



