Silvery Spleenwort IOI 
mountain streams, etc.; particularly in or on the outskirts of 
cold woodlands. 
Range. Nova Scotia and New Brunswick to Minnesota, IIli- 
nois, Alabama, and Georgia. 
Athyrium thelypteroides. Desvaux, Mém. Linn. Soc. Paris. 6: 266. 1827. 
Asplenium thelypteroides. Michaux, Fl. Bor. Am. 2: 265. 1803. 
Athyrium acrostichoides. (Sw.) Diels, Die Nat. Pflanzeuf. 1°:223. 1899. 
Asplenium acrostichoides. Swartz, Shrad, Journ. Bot., 18007: 54. 18or. 
Younc 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 Pls. XXIII, XXIV. 
The early pinne 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 pinne’s midveins, become 
well marked, oblong, slightly often obscurely toothed segments, 
+n which the branches of the pinne’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 P]. XXV, Fig. 1. 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 pinne’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 
