﻿THE FERN BULLETIN 



53 



collateral vascular bundles ; stems increasing in diame- 

 ter by a cambium zone : heterosporous. the sporophylls 

 in cones. 



Sphexophylleae. 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 heterosporous. the sporophylls in cones. 



Hydro pterides. 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. Quillworts. 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 meg'asporangia large, borne 

 singly, sunken in the expanded bases of the leaves, 

 eusporang'iate. Gametophytes very much reduced; 

 spermatozoids spirally coiled, multiciliate. 



Selagixelleae. Selaginellas. 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 meg'asporangia single in the axils of the sporo- 

 phylls. Gametophytes small and short-lived : sperma- 

 tozoids very minute, biciliate. Some fossil species de- 



