170 Rhodora [SEPTEMBER 
Nevertheless, the commonly accepted range of some of our most 
familiar ferns is much more extended than is usual in the case of 
Phanerogams, and not infrequently is quite at variance with the ławs 
of distribution which have been worked out for the latter type of 
plants. ’ 
In a recent examination of the ferns of the Selkirk Mountains it 
occurred to the author to make a critical study of some of the forms 
which are supposed to have a very wide and somewhat anomalous 
range. It appeared that, in the treatment of closely related species 
of ferns, and of races within the species, too much reliance had been 
placed on such superficial characters as details in the form and cutting 
of the fronds, characters of a kind which botanists have found to be 
peculiarly unreliable in most groups of plants. It seemed that a 
study of such technical characters as the size, form and sculpture of 
the spores, and details of the structure of the sporangia, sori, indusia 
and scales, might reveal characters of a more stable nature than the 
purely vegetative ones usually employed. As will be seen in the fol- 
lowing series of papers, this study has led, in the case of several of our 
common groups of ferns, to the separation of species and varieties, in 
other cases to the recombination of forms supposed to be distinct, and 
the races characterized by the same technical characters have been 
found in all cases to have geographical ranges quite in harmony with 
well-known laws of the distribution of flowering plants. 
I. THE GENUS ATHYRIUM AND THE NORTH AMERICAN 
FERNS ALLIED TO ATHYRIUM FILIX-FEMINA. 
1. THE Genus ATHYRIUM. 
Fern genera are traditionally unsatisfactory, and in no part of the 
group are they more so than in the alliance of which the lady fern is a 
member. These form a naturally compact group in which it is some- 
times difficult to distinguish clearly between the species, yet in some 
treatments of the ferns the species described below have been rele- 
gated to as many as three different genera, while Athyrium Filix-femina 
itself has been placed by reputable authors in at least four of the larger 
fern genera. This is largely due to the attempt, current throughout 
the latter part of the eighteenth, and much of the nineteenth century, 
