102 Silvery Spleenwort 
often becomes an incipient or more developed midvein with 
simple branches (Pl. XXV, Fig. 2). 
It will be seen that in one sense the last step is mere repetition 
of what has gone before, and that it accords with this fern’s 
disposition to lengthen and point its leaf-segments as they de- 
velop, to enlarge teeth into segments, and to develop branches 
of midveins into midveins with branches. The leaves with 
the highly developed pinne are sometimes sterile, sometimes 
fertile. While less common than the leaves that do not repre- 
sent the height of the leaf-development, they are to be looked for 
in any luxuriant mature plant, and are likely to occur on the 
same plant with less well-developed leaves as it advances in 
development: leaves also are likely to occur in which some of 
the pinne’s segments are highly developed and others not. 
There is apparently nothing here to denote subspecific variation, 
or even monstrous development, or to entitle either the markedly 
highly developed leaves or markedly less well developed but 
mature leaves to a distinctive name. Yet the highly developed 
leaves have received at least two such names, and in one instance 
the less well developed have been interpreted as a variety of the 
highly developed.* 
In this fern each sorus is borne on a vein which stands, or on 
* “Var. serratum” Lawson is apparently based upon the highly developed leaves. 
See Canad. Nat. 181. 1864. ‘Athyrium acrostichoides thelypteroides” Gilbert is based 
upon the less well developed leaves. See Fern Bulletin, 8: 9-10, 1900. In his “List of 
North American Pteridophyta,” 15. 1901, Mr. Gilbert apparently reverses this arrange 
ment, calling the highly developed leaves the variety or ‘“‘form,”’ to which he gives the 
name “A. thelypteroides f. acrostichoides.”’ 
Swartz appears to have drawn his original definition of his A. acrostichoides from the 
highly developed leaves, judging from p. 82 of his Synopsis Filicum, where this definition 
is quoted and appears side by side with a short definition of Michaux’s A. thelypteroides, 
which Swartz evidently considered distinct. The two definitions point respectively to the 
highly developed and the less well developed leaves of this fern. 
