63 
be, or have boon, Avorld-Avide in distribution; it should be found, in its 
essentials in the various tribes, excepting as sonic tribes may probably 
be derived from others, rather than directly from the primitive form; 
and, in tlic more ancient tribes, it should be possible to outline tlie devel- 
opmont of the more recent and more specialized genera from those most 
like the generalized primitive form. 
I believe that this primitive fern, through whatever stages it may 
have been evolved, from which all Polypodiacem have been derived, was 
a terrestrial plant of hnmid woods, Avith a short, stout rhizome, w^ith 
ample, compound or decompound loaves, the fertile and sterile not differ- 
entiated, with nonarticulate stipe, and with small, distinct, more or 
less round sori. I shall show that such ferns as these meet every denuind 
laid down in the preceding paragraph. Nearly or exactly this primitive 
fern exists now in the genus Nephrodium, more particularly in the 
subgenus Lastrwa. As is true of all generalized types, it is impossible 
b}' any character, or any practicable combination of characters, to diagnose 
Lastrwa as a natural group, retaining all species which as a matter of 
highly probable genetic affinity should be included and excluding all 
plants the genetic affinity of which is very remote. Lasirwa merges into 
Goniopteris througli species with a single pair of irregularly anastomos- 
ing veinlets; or else, as at least in part is probably the case, we include 
in Lastrcea a considerable number of species descended through Goniop- 
teris but with free veins; in cither case the natural separation of the two 
groups is not feasible. The line between Lastrcea and Pleocnemia is but 
little less vague. 
. The indusiiim of Lastrwa is utterly inconstant. The lines between 
Phegopteris and Dryopteris and between Goniopteris and Cyclosorus 
appear to me to be purely artificial; nor is the shape of the indusium, 
when present, invariable. It is not rarely peltate in Nephrodium immer- 
sum, just as it is sometimes reniform in Aspidium angulatum, and in the 
plant known as Mesochlaena it is diplazioid in form. Again the sorus is 
elongate, in those immediate relatives of Nephrodium nrophylhim some- 
times called Meniscium,. And even the nonarticulate stipe is not a con- 
stant character, for my Xo. 1112 is unmistakably a Lastrcea, with as 
evidently articulate a stipe as that of any other scandent fern. While 
the fronds are characteristically compound, there are exceptions, and 
there are species, both in Lastrwa and Goniopteris, with the fronds sub- 
dimorphous. 
As Nephrodium is altogether the most generalized and indefinable 
genus of ferns, its general characters — compound, ample, thin fronds; non- 
articulate stipe; short, stocky rhizome, and round sori— can be accepted 
as those of the most generalized, and therefore primitive Polypodiacem. 
Lastrma is also thoroughly cosmopolitan. 
Goniopteris is more specialized, having a relatively Citable frond-form, 
almost alwavs simply pinnate, and firmer texture. Glandular trichomos, 
