THE FERN BULLETIN 



53 



collateral vascular bundles : stems increasing in diame- 

 ter by a cambium zone : beterosporous. the sporophylls 

 in cones. 



Sphenophylleae. Fossil. 



Paleozoic plants of tree-like aspect and dimensions, 

 with solid jointed stems with a central triarch vascular 

 bundle : leaves wedge shaped, comparatively small ; 

 probably beterosporous, the sporophylls in cones. 



Hvdropterides. Water- ferns. 75 species. 



Sporophyte with a horizontal rhizome or floating on 

 the surface of the water ; leaves alternate or whorled ; 

 microsporangia and megasporangia borne together en- 

 closed in sporocarps. leptosporangiate. Gametophytes 

 developing entirely within the spore walls or protrud- 

 ing only slightly, very short lived; spermatozoids large, 

 spirally coiled, multiciliate. 



Isoeteae. Quill worts. 60 species. 



Sporophyte with a short tuberous stem with a pecul- 

 iar type of secondary thickening and with long, erect, 

 grass-like leaves which have a ligule : roots dichoto- 

 mous : microsporangia and megasporangia large, borne 

 singly, sunken in the expanded bases of the leaves, 

 eusporangiate. Gametophytes very much reduced ; 

 spermatozoids spirally coiled, multiciliate. 



Selagixelleae. Sebginellas. 500 species. 



Sporophyte dorsiventral or erect, with monopodial 

 or dichotomous branching and dichotomous roots; 

 leaves small, opposite or spirally arranged, ligulate; 

 cells often with a single chloroplast ; sporophylls in bi- 

 sporangiate cones, the eusporangiate microsporangia 

 and megasporangia single in the axils of the sporo- 

 phylls. Gametophytes small and short-lived ; sperma- 

 tozoids very minute, biciliate. Some fossil species de- 



