1917] Butters,— Studies in Ferns — Athyrium 177 
As Copeland has well pointed out,! Athyrium and Dryopteris are 
both relatively primitive genera of Polypodiaceae, presumably with a 
common origin, and between the more undifferentiated species of the 
two genera there is really no definable difference. In both groups, 
species occur with small hippocrepiform, round and cystopterid sori 
mingled on the same frond, and it becomes necessary to judge such 
cases, each on its individual merits. Thus Athyriwm mongolicum 
(Franch.) Diels, which has many cystopterid and dryopterid sori 
mingled with other athyrioid ones is more closely allied to the Filiz- 
femina group of Athyria, than to any species of Dryopteris, while 
Dryopteris Schaffneri (Fée) C. Chr., with a similar assortment of sori, 
is obviously a member of the somewhat specialized section Goniopteris 
of the genus Dryopteris. Similarly, in one of the species discussed in 
this paper, Athyrium alpestre (Hoppe) Rylands, evidence from the 
sori is at best very slight, and in some of its forms, as, for example, 
that found in America, such evidence is entirely wanting, yet, so 
closely do some of its forms approach to certain forms of the common 
lady fern, that the two species can scarcely be kept separate, and there 
can be no question of the generic position of Athyrium alpestre in any 
natural classification of ferns. 
In this connection, it is well to note that Christensen ? has found 
the type of pubescence very useful in classifying ferns of the genus 
Dryopteris, and it bids fare to be equally useful in delimiting the 
groups of the genera Athyriwm and Diplazium, and in indicating the 
true affinities of certain anomalous species. 
In the direction of Diplazium the limits of the genus Athyrium are 
even harder to define. As stated above, Milde è decided finally that 
this is an impossible task, and he then merged the two genera, while 
Copeland holds £ that the Asiatic Diplazia have had a multiple origin 
from the typical Athyria, and therefore cannot properly be regarded 
as constituting a genus. The Asiatic forms of Diplaziwm, and of 
Athyrium also, are certainly much more complex in their relationships 
than the American forms, and the final settlement of this question 
will depend on a careful working out of the lines of evolution of the 
1 Copeland, E. B., A Revision of the Philippine Species of Athyrium. Philip. Journ. of Sci. 
Bot. iii. 285 (1908). 
2 Christensen, C., On a natural Classification of the species of Dryopteris. Biol. Arb. 
tileg. Eug. Warming (1911). > 
3 Milde J., Ueber Ath. etc., Bot. Zeit. xxviii. 329 (1870). 
4 Copeland, E. B., loc. cit. 
