GENERA OF FERNS. 381 
seated in a cell ; between each cell is a slightly elevated ridge, 
which, on the removal of the sporangia, exhibits the form of 
across, with the punctiform receptacle in its centre. 
128. Merrensia, Willd. Sw. Presl. 
(Gleichenie sp. R. Br. et Auct., Sticherus, Presi.) 
Veins pinnately or simply forked, evident. Venules direct, 
free, the exterior one fertile. Sporangia medial, superficial, 
3 to 8 or more, constituting round globose naked, or tricho- 
phorous sori. 
Rhizoma creeping. Fronds rigid, from 1 to 6 feet high, 
many times dichotomously branched (seldom simple) and pin- 
natifid ; branches (pinne) pinnatifid ; lacinie uniform, linear, 
entire, rarely dentate, smooth, glaucous or villose. | 
Examp. 1. M. simplex, Desv. 2. M. nervosa, Kawlf. 3. 
M. glaucescens, Willd. 4. M. Hookeri, J. Sm. (Gleichenia 
Hermanni. Hook. et Grev. ic. fil. t. 14). 5. M. dichotoma, 
Willd. (Gleichenia Hermanni, R. Br. 6. M. rigida, J. Sm. 
7. M. bifurcata, Blume. 8. M. furcata, Willd. (Mertensia 
decurrens, Radd.) 9. M.immersa, Kaulf. 10. M. flabel- 
lata, R. Br. 11. M. Cunninghamii, Hew. 12. M. gigantea, 
Wall. 13. M. excelsa J. Sm. | 
Illust. Hook. et Bauer gen. fil. t. 39, Hook. et Grev. ic. fil. 
t. 14, 15. 
Obs. The larger habit, plane lacinie, evident venation 
and medial sori, readily distinguish this genus from Glei- 
chenia. The genus Sticherus of Presl is by that author cha- 
racterised as distinct from Mertensia, by its reticulated 
venation. I possess genuine specimens of one of the species 
(Gleichenia lanigera D. Don) and also of what I take for the 
M. levigata Willd. (which is a doubtful species of Sticherus, 
according to Presl.) Neither of these exhibits reticulated 
veins, and the very great similarity of all the species in this 
genus renders it difficult to determine what are really dis- 
tinct. Instead of Don’s Gleichenia lanigera being the type 
