
4 THE BRITISH FERNS. 
in Asplenium, and may be called crescentic. From Hemestheum, 
Lastrea, Lophodium, and Dryopteris [all forms of Lastrea as defined 
in this work], it differs in having the clusters of capsules linear 
rather than circular, attached to the side rather than to the back of 
the vein, and the involucre which covers them attached longitudinally 
rather than transversely. Whether it be distinct from Pseudathyrium 
is a graver and more difficult question. My own inclination is to 
unite them ; but supposing this the philosophical solution of the 
question, how are we to manage the generic name? The species of 
Pseudathyrium are emphatically excluded from Roth's genus Athy- 
rium by that learned author's definition of the involucre, and the 
species of Athyrium cannot be comprised in the genus Pseudathyrium, 
because that is distinguished by the absence of all involucre. Again, 
the two genera will not blend in one, because Roth's type species 
of Athyrium is Asplenium fontanum, and his second species Asplenium 
Halleri. Antieipating the time when characters founded on the 
absence, presence, size, or form of an involucre among Filicaceœ 
will be regarded as of no higher importance than those founded on 
the absence, presence, size, or form of a petal among Ranunoulacee, 
I cannot but also antieipate the eventual union of plants so similar 
in habit as Filie-femina and alpestre, in a genus to which a new 
name may perhaps be given. The difficulty, in such an arrange- 
ment, lies in releasing the botanieal mind from the cramping 
trammels which it has so long regarded as necessary. It is im- 
possible for botanists to neglect the involucre ; its characters are not 
only patent and manifest, but, what is a matter of still greater 
importance, are susceptible of perspicuous definition. Still, if the 
botanist seek to found on its variations higher groups than little 
clusters of species, which, like those known under the names of 
ilvense, fragile, aculeatum, dilatatum, Filix-mas or Filix-femina, may 
or may not be divided into species at the option or caprice of each 
successive author, he will find himself inextricably involved in the 
most tangled and unnatural combinations. With regard to the 
genus Athyrium, as composed by Roth of two groups, I am clearly 
of opinion that it cannot stand; the fontanum group and the Filiz- 
` femina group will not harmonise: then if we restrict the genus to 
the typical or fontanum group, we cannot, by Roth's definition, 

