Silvery Spleen wort 101 



mountain streams, etc.; particularly in or on the outskirts of 

 cold woodlands. 



Range. Nova Scotia and New Brunswick to Minnesota, Illi- 

 nois, Alabama, and Georgia. 



Athyrium thelypteroides. Desvaux, Me*m. Linn. Soc. Paris. 6: 266. 1827. 

 Asplenium thelypteroides. Michaux, Fl. Bor. Am. 2: 265. 1803. 

 Athyrium acrostichoides. (Sw.)Diels, Die Nat. Pflanzeuf. i*:22^. 1899. 



Asplenium acrostichoides. Swartz, Shrad, Journ. Bot., 1800": 54. 1801. 



YOUNG leaves of Athyrium thelypteroides can be easily rec- 

 ognized in the field by their peculiar specific texture and the short 

 hairs studding their upper surface. 



The venation is pinnate. 



The early forms of the leaf are shown in Pis. XXIII, XXIV. 



The early pinnae are very short and blunt. In the course 

 of development they, as well as the leaf-blade itself, lengthen 

 more and more and become at last drawn out at apex into a long 

 point. 



In the mean time their segments, which at first are mere teeth 

 or lobes or barely defined, and contain each a simple, once-forked 

 or slightly more complex branch of the pinnae's midveins, become 

 well marked, oblong, slightly often obscurely toothed segments, 

 in which the branches of the pinnae's midveins have become well- 

 defined midveins with simple branches which occupy the seg- 

 ments' teeth. At this stage of development the leaf appears as 

 in PL XXV, Fig. i. In PL XXV, Fig. 3, is shown an enlarged 

 section of a pinna of a leaf at this stage. 



Finally, in the most highly developed leaves, the pinnae's seg- 

 ments lengthen and become slightly pointed, the segments' teeth 

 enlarge and the incisions between them deepen, so that they 

 become lobes rather than teeth, and the vein occupying each lobe 



