272 Bower. — Studies in the Phytogeny of the Filicales. 
where scales or hairs form an efficient covering. In G. linearis (=G. di - 
chotoma) they are highly specialized for the protective function (Goebel, 
‘Organography,’ ii, p. 319, Fig. 206). In general form the leaves of these 
two species are very widely expanded, and are among the largest of the 
Mertensia division of the genus. They are thus in strong antithesis to the 
leaves of the Eu-Gleichenia division, which have the leaf-area reduced, 
probably in relation to a xerophytic habit. 
The surface appendages have been too much neglected as a basis for 
comparison in Ferns. In many systematic treatises they are ignored. 
Even in the excellent work on the Filicales by Diels (Engler u. Prantl, ‘Nat. 
Pflanzenfam.,’ i. 4) theiFoccurrence and peculiarities are often left unnoticed 
in cases where, as in Gleichenia and Alsophila , they have a comparative 
value. Long ago, however, the value of surface appendages for phyletic 
comparison was noted by Prantl (‘ Schizaeaceen ’, p. 37), who concluded that 
simple hairs were the primitive type, but that in many circles of affinity 
they developed in a flattened form. The ramentum or scale is thus deriva- 
tive or secondary. This distinction of hair and scale was adopted by Max 
Kuhn as the basis of a classification of the Polypodiaceae, which he divided 
into Chaetopterides , with hairs, and Lepidopterides , with flattened scales. 
Against the use of this as a leading criterion, which resulted in an unnatural 
juxtaposition of genera, Prantl protested (‘ System der Fame ’, ‘ Arb. K. Bot. 
Gart. z. Breslau,’ p. 13). But, nevertheless, he adopted the existence of the 
scale as an expression of a progressive step of organization. This is the 
way in which the hair-scale criterion should be used as an indication of 
a relatively primitive or of a relatively advanced condition, which may 
be brought with other progressive features into a general argument ; but 
with the full knowledge that the advance from hair to scale has probably 
been made in various phyletic lines, and that it does not necessarily progress 
coincidently with other features of advance. 
An examination of the dermal appendages of Gleichenia brings some 
interesting results. Of the section Eu-Gleichenia three species have been 
examined, viz. G. polypodioides , Sm., G. dicarpa , R. Br., and G. circinnata, 
Sw. In all of them broad scales were found protecting the dormant leaf- 
apices, as also on the leaf-bases and the rhizomes. But with them are 
associated hairs. In the first two species these were pale and soft, but in 
G. circinnata they were stiffer, and very beautiful transitions can be found 
between simple brown hairs and those which are branched and tufted, and 
finally to broadened scales, with stiff hairs projecting from their margins. 
It is as though the bases of the hairs had broadened to form the scales, 
and this is their probable origin. The hairs and scales fall off early from 
rhizome and leaf. It appears thus that both hairs and scales are present, 
probably with constancy, in Eu-Gleichenia, and this is biologically in 
accordance with their xerophytic habit. 
