120 NATURAL HISTORY BULLETIN. 



That both epiphytes and tree-ferns gradually adopted their 

 present habits is suggested both by the requirements of their 

 surroundings, and by forms which to-day are intermediate 

 between the strictly terrestrial sessile forms, and the epiphytes 

 on one hand and tree-ferns on the other. The ferns which 

 were collected on Ometepe are for the most part terrestrial. 

 The occurrence in this part of Nicaragua of a distinct dry 

 season which is less favorable to the development of epiphytes, 

 no doubt accounts for the small number of such species, only 

 one of the Ometepe list, Poly-podium incanum, having this 

 habit, — though one other, Notholcena brac/iypus, grows on 

 almost bare volcanic rocks, and is really epiphytic. No tree 

 ferns were found on Ometepe. 



At Castillo, and more particularly at Greytown, the dry 

 season is less marked, the forests better retain their vigorous 

 verdure, offering plenty of moisture and shade to the exposed 

 rootstocks and roots of epiphytes, and the number of such 

 species among all plants is much greater, — the ferns forming 

 no exception. Nearly one-half the species from Greytown 

 and vicinity are epiphytes, and three are tree-ferns. The 

 geographical distribution of these ferns is interesting. Only 

 two species, Gymnogramme tartarca and JYephrodium conter- 

 minum, were found common to Ometepe, Castillo and Grey- 

 town. Five of the Ometepe species were also found at Castillo, 

 and fifteen of the Castillo species were found at and near 

 Greytown. That a greater number was not found common 

 to the two latter localities is probably due to insufficient 

 exploration at Greytown, for the conditions at these two 

 places are somewhat similar, the greater extent of swampy 

 lowlands at Greytown constituting the chief peculiarity. This 

 variety in the fern-floras of localities not very remote from 

 each other indicates the possibilities of a thorough exploration 

 of the San Juan Valley and its adjacent highlands. Less than 

 one thousand species of vascular plants have been reported 

 from Nicaragua, 1 and about one-seventh, or 135 2 are Ferns. 



1 Biologia Centr all- Americana, vol. iv, p. 218. The number given is 984. 

 s Zbid., p. 200. To this should be added 19 additional species reported by 

 Fournier in Serlum A r ic, making a total of 154. 



