1917] Butters,— Studies in Ferns — Athyrium 171 
to rely entirely upon the structure of the sorus and indusium for 
generic distinctions and delimitations. This attempt is now seen to 
have resulted in an artificial system entirely comparable to the Lin- 
naean system of classification of flowering plants. In some cases, 
particularly in highly specialized groups, it resulted in bringing 
together related forms, but it often led to obvious absurdities both of 
aggregation and of separation. It naturally resulted in particularly 
illogical results in such a group as Athyrium, where the sorus is a 
peculiarly variable and unstable organ. 
The genus Athyrium Roth ex Mertens! was originally founded 
entirely upon soral characters which further investigation has shown 
to be illusory. In view of this it is not strange that botanists like 
Mettenius and Hooker should have found it impossible to maintain 
the genus, and should have considered it merely as a section of Asplen- 
ium. In 1866 and 1870, Milde, however, in two notable papers? 
showed that the lady fern and its relatives differ in several respects 
from the true Asplenza, and refounded the genus Athyrium on a firmer 
basis. He laid particular stress on the structure of the scales in the 
two genera and on differences in the vascular structure of the frond. 
He also pointed out that Phyllitis (Scolopendrium) and Camptosorus 
agree with Asplenium in both of these respects, while Diplazium, sev- 
eral of the other genera of Asplenicae, and the more primitive genera 
of the Aspidicae agree with Athyrium. In his second paper he confirms 
his earlier results so far as the differences between Athyrium and 
Asplenium are concerned, but he confesses that he is unable to main- 
tain any generic difference between Athyrium and Diplazium, and he 
accordingly transfers a long list of species from the latter genus to 
Athyrium. 
In general, the distinctions pointed out by Milde hold very well, 
1 Auszug eines Briefes von Hrn. Prof. Mertens in Bremen an den Herausgeber, Rémer’s Archiv 
fiir die Botanik, ii. pt. 1, 105 (1799). 
Roth, A. G., Tentamen Florae Germanicae, iii. 58 (1800). 
Roth’s diagnostic character was the recurved sorus. Though his description of the genus 
was evidently based almost wholly on A. Filix-femina, which has since been considered the type 
of the genus, and on its various European forms, which he treated as distinct species, he listed 
as the first species A. fontanum, a genuine Asplenium with no close affinity to the lady fern. 
This species often has some of its sori recurved, and rarely has a few of them hooked as in true 
Athyrium. Roth’s reason for placing this fern first was evidently merely that he was arrang- 
ing all of the species in order, with the least compound first. That he did not consider it typical 
is evident, as it differs in several respects, notably in its entire indusia, from his generic descrip- 
tion. 
2 Milde, J., Das Genus Athyrium. Bot. Zeit. xxiv. 373 (1866). 
Id., Ueber Athyrium, Asplenium und Verwandte, Bot. Zeit. xxviii. 329 et sqq. (1870). 
