1046 



frond separated from the parenchyma by the pressure of the growing 

 capsules, although the great similarity of its structure to that of the 

 epidermis has been so often pointed out; but rather a separate and 

 distinct part, as much so as the veins, the capsules or the scales : in 

 the Hymenophyllacege the bivalved involucre is quite another affair ; 

 it is perfectly continuous with the edge of the frond, and is very evi- 

 dently formed of its tvro cuticles. The office of the involucre in the 

 Polypodies has not, we believe, been demonstrated with precision, 

 and it is quite possible that the involucre in the Hymen ophyllacese 

 may perform exactly similar functions ; but the parts are not identical, 

 and the involucre of Hymenophyllum appears to us rather the ana- 

 logue of the inflected margins of an Adiantum, or an Allosorus, than 

 of the peltate involucre of a Polystichum. The texture of the frond 

 in the Filicacese is generally somewhat coriaceous or slightly fleshy, 

 and the transparent veins, when viewed from above, appear to be sunk 

 in its substance : in the Hymenophyllacese the reverse is the case, the 

 frond being very thin and membranous, and the veins stout, winged, 

 prominent and opaque. Thus the structure of these interesting plants 

 seems to lead us to the conclusion that they form a part of the Filica- 

 ceee or true ferns, while the points in which they difi"er from the rest 

 are so numerous, that we are compelled to consider them the most 

 distinct and detached division of that extensive and diversified order. 



We are fully aware that exceptions occur to all these characters : 

 for instance, Robert Brown's Loxsoma seems to have something of a 

 fleshy or leathery frond, with free, setiforra involucres and stipitate 

 capsules; and other instances of departure from typical character 

 might without difficulty be pointed out. 



The Hymenophyllacese are divided by Presl into nineteen genera, 

 composing two tribes, Trichomanoideae and Hymenophylloideae ; the 

 first of these is again divided into two sections, Trichomanese and 

 Didymoglosseae. The genera of Trichomanese are these : Feea and 

 Hymenostachys of Bory, Didymoglossum of Desvaux, and Lecanium, 

 Cardiomanes, Trichomanes (restricted), Ragatelus, Cephalomanes, 

 Neurophyllum, Microgonium, Abrodictyum, Meringium and Hemi- 

 phlebium of Presl. The genera of Hymenophylloideae are Leptocio- 

 nium, Myrmecostylum, Ptycophyllum, Hymenophyllum (restricted), 

 Sphserocionium and Hymenoglossum of Presl. 



The characters given to the Trichomanoideae are these.* 



* We prefer giving the quotations untranslated, believing that all botanists who 

 may honour us with a perusal of these pages, will prefer the original to any version 

 which it is in our power to make. 



