CHARACTERS OF TRIBES AND GENERA. 189 



they are epigeous, of a flaccid soft texture, easily affected 

 by drought ; the well-known Lastrea Filix-mas, L. Oreop- 

 teris, and L. dilatata being examples ; or they are more 

 firm, hard, and spiny, as in Polystichum aculeatum and 

 allies. 



The most important divisional characters consist in the 

 veins being free or anastomosing in various ways, and in 

 the sori being naked or furnished with an indusium, which 

 in some is very small and fugacious, soon becoming obli- 

 terated, and which leads to some species being placed in 

 indusiate genera by some authors, while others place them 

 among the non-indusiate. 



The normal character of the indusium is either lateral 

 (interiorly attached) or peltate ; in some multifid fronds, 

 such as Lastrea deparioides, the indusium appears to coincide 

 with the crenule or dent of the margin, so as to form a 

 cyst similar to that of Microlepia, and in Trichiocarpa it is 

 exserted beyond the margin in the form of a calyciform 

 cyst, as in Deparia. In AmpTiiblestra the sporangia are 

 produced in an irregular row close to the margin, which 

 is in flexed in the form of an indusium like that of Pteris, 

 but from which it differs entirely in habit and venation, 

 which is that of Aspidium ; and as regards Isoloma, 

 although it has marginal sori similar to Lindscea, it never- 

 theless differs entirely in habit, which agrees perfectly 

 with that of Nephrolepis. In Hypoderris the sori are 

 discal and furnished with a small membraneous calyciform 

 indusium similar to that of Woodsia. Although these four 

 genera differ in the nature of their fructification from the 

 normal character of the indusiate Phegopteridece, I never- 

 theless deem it best to place them in it, and as near as 

 possible in contiguity with the genera to which they are 

 most nearly allied in habit and venation. 



