7 
than the acroscopic one; the basiscopic secondary pinnules thus are nos. 1, 3, 5 
etc., the acroscopic ones nos. 2, 4, 6 etc. This catadromous arrangement 
is the rule in species of Eudryopteris and Ctenitis. 
In other species of a polystichoid habit, i. e. the acroscopic basal pinnules 
of the 2nd, 8rd or 4th order are much more developed than the basiscopic ones, 
which gives the partitions of any order a characteristic shape, cuneate at the back, 
auriculate in front, the acroscopic pinnule is always the first, while the basiscopic 
One is moved far up from the rachis and, as arule, much smaller, so that space 
is gained for the large acroscopic pinnula below. This anadromous arrange- 
ment (fig. 2) is characteristic of all species of Polystichopsis. 
This characteristic difference between anadromous and catadromous decom- 
posite leaves can also be observed in the arrangement of the basal veins of segments 
of the ultimate order, where these toward the apex of the pinnula of the previous 
order become sessile or confluent. We have here two types: | 
1. The first basal vein of the ultimate order is the basiscopic; it runs out from 
the very base of the midrib of the ultimate segment, or, frequently, from the 
midrib of the pinnula of the former order. So in Ctenitis (fig. 1 b). 
2. The first basal vein is the acroscopic One, it runs out from the midrib of the 
ultimate segment a little above its base, the basiscopic basal vein is no. 2 
and is very oblique. So in Polystichopsis (fig. 2 b). 
Between these two principal types an intermediate type is to be found in the sub- 
genus Parapolystichum, and MEerrEeNius named the species belonging here Subpoly- 
slichoidee. The arrangement of the ribs of these species is as a whole catadromous, 
but the veins of the ultimate order show considerable inconstancy in this character 
in the same leaf, as the basiscopic as well at the acroscopic basal vein may be 
the first; frequently they are opposite, still the ultimate pinnule are, as a rule, 
decidedly polystichoid with the acroscopic basal segment considerably enlarged, 
while the basiscopic one is small and oblique, exactly as in the species of Poly- 
stichopsis. 
The number of species adopted in the two parts of this monograph is 347. 
In North America 17 more species are to be found, thus the whole number of known 
American species af Dryopteris is 364. No doubt several others may exist; I have 
had for examination several defect specimina, which certainly belong to undescribed 
“Species, and some few species described recently by other authors I have not seen. 
Some of these will probably prove to be identical with species described in this 
work. Some few of the species adopted by me may possibly be found to be too — 
_ Weakly characterized, when more material is collected, and must be reduced to be | 
