194 J. SMITH ON THE GENERA OF FERNS. 



measure to depend upon local circumstances in connexion 

 with its growth ; for I possess specimens of fertile fronds 

 scarcely or not at all contracted. Schott has proposed to form 

 the Aspidium (Lastrea), Thelypteris of Swartz into a genus 

 under the name of Thelypteris, as also Aspidium (Lastrea) 

 Filix-mas of Swartz and its allies, under the name of Dryop- 

 teris — two genera in my opinion not at all tenable; for, allow- 

 ing that there is some diiference in the structure of the indusi- 

 um of these species, and the fertile frond of Thelypteris being 

 slightly contracted, with the margin revolute, yet I cannot be 

 induced to adopt his genera; for, on viewing the whole of the 

 species, they appear to form a gradual transition in habit and 

 character from one to another, and even in habit, passing 

 into the following genus, Pohjstichum. 



The Nephrodium hirsutum of Don, {Aspidium eriocarpum, 

 Wall.) has been characterized by Kunze as a distinct genus, 

 under the name of Hypodematium : he separates it on account 

 of its having, according to his view, pedicillate sori analogous 

 to the genus Spharopteris. Since I have seen his character 

 and figure of the genus, I have again carefully examined the 

 species; and from what I have seen, I must still continue to 

 differ from that author in considering the sori to be pedi- 

 cillate. The only peculiarity is in the receptacle being (as in 

 all large sori,) more elevated than in the generality oi Aspi- 

 dieisi but it certainly has no pedicel or footstalk, the sporan- 

 gia being borne from its base to its apex : on removing the 

 sorus, the force used will often tear away with it a small length- 

 ened portion of the epidermis of the venule, which, viewed in 

 certain positions, presents the appearance of a footstalk to 

 the receptacle, as represented at t. 28, Jig. d. of Kunze's^rt«- 

 lecta Pteridographica. 



The species of Lastrea, with bipinnatifid fronds, are so 

 similar to Nephrodium, that the two genera can only he 

 known from each other, by none of the venules of Lastrea 

 being anastomosed. 



