PTERIDOPHYTA 



275 



The Osmundacese are probably old forms which, have largely dis- 

 appeared. At present about a dozen species are known. Of these, 

 three species of Osmunda occur in the eastern United States, but 

 none are found on the Pacific coast. The other genera, Todea and 

 Leptopteris, belong to the southern hemisphere. 



Family 2. Gleicheniaceae 



The Gleicheniaceae comprise about twenty-five species of Ferns, 

 principally confined to the Tropics, but extending to the extreme 



B 



L 



FIG. 242. Gleichenia dichotoma. A, pinnule, showing the position of the sori, s 

 (X 4). B, ventral, C, dorsal, view of the ripe sporangium (x 85). D, vascular 

 bundles of the petiole and stem of Gleichenia sp. ; the dark masses represent the 

 xylem ; ph, phloem ; en, endodermis. (D, after POIRAULT.) 



southern part of South America. Except for the monotypic Stro- 

 matopteris moniliformis, they all may be included in the genus 

 Gleichenia (Fig. 242). 



Gametophyte. The gametophyte is intermediate in character between that 

 of Osmunda and the higher Leptosporangiates. 



Sporophyte. The sporophyte in Gleichenia has a slender creeping rhizome, 

 which is inonostelic. The leaves are in most species dichotomously branched, 

 and have an unlimited apical growth, so that they become very long, and climb 

 over shrubs and trees, often forming almost impenetrable thickets. Very often 



