THE ROUND-LEAVED FILMY FERN. 



Trichomanes reniforme. 



By Williard N. Clute. 



The family Hymenophyllacese to which the filmy ferns 

 belong, is one of the most interesting of fern families. In 

 its ranks are to be found the very smallest ferns in the 

 world, some of them, as in the case of our own Tricho- 

 manes Petersii of the southern States, so small that the 

 mature plant, or several of them, may be concealed under 

 one's finger. There are a few forms that occur in tem- 

 perate regions, but the majority are to be found in 

 moist places in the tropics. Given a warm region with 

 plenty of moisture, and the filmy ferns are likely to be 

 present in abundance. The writer well remembers taking 

 shelter from the rain under a leaning tree trunk in the 

 forests of Jamaica, and watching the rain-drops trickle 

 down from no less than eleven different species of filmy 

 ferns, while the shower continued. The cause of the 

 great dependence of these ferns upon moisture, is that 

 their fronds are usually but a single cell in thickness, and 

 being unprotected by a thick epidermis, as the ferns of 

 dry regions are, would dry out very quickly in places 

 where the air is not constantly moist. They are thus 

 well named filmy ferns. 



There are two great genera in the filmy fern family 

 named respectively, Hymenophyllum and Trichomanes. 

 The members of both are very much alike in appearance. 

 The principal distinguishing feature being found in the 

 form of the fruiting parts. The sporangia are not found 

 in sori on the backs of the fronds, as the ordinary ferns 

 fruit. Instead, some of the marginal veins project from 

 the edges of the fronds as slender bristles, and the spor- 

 angia are clustered around this. The indusium is a cup- 

 like structure surrounding the base of the bristle, and this 

 is often spoken of as the involucre. If the involucre is 



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