122 DRYOPTEROID FERNS [CH. 



genera referred to the Aspidieae by Diels may be held as forming a coherent 

 group of Ferns, related to one another though subject to modifications as to 

 detail. The first step will be to consider the probable connections downwards 

 of that central type which is represented by the Common Male Shield 

 Fern \ 



Dryopteris FILIX-MAS (L.) Schott 



The essential features of the Male Shield Fern have been described already 

 in Vol. I, Chapter I. The basket-like habit with ascending stock is similar to 

 that seen in dwarf Tree-Ferns (Fig. 31), and it is very closely shared by 

 PerancDia and Diacalpe, which also have similar pinnate leaves and open 

 venation: their chaffy scales too correspond, while the superficial position 

 of the sori of them all and the insertion of each upon a vein in its course 

 towards the margin are as in the Cyatheaceae and Gleicheniaceae. 



Most of the leaves of the Male Shield Fern bear each a bud laterally, some 

 distance above the leaf-base (Vol. I, Fig. I, B, C). These buds raise the 

 question whether each is to be regarded as a product of unequal dichotomy 

 of the axis, the bud representing the weaker shank carried up upon the 

 leaf-base: or whether it is an adventitious development (Vol. I, p. 78). The 

 fact that dichotomy is prevalent in the creeping species oi Dryopteris lends 

 some degree of probability to the former alternative (Fig. 32). Such difficulties 

 of interpretation in terms of dichotomy appear to be inherent in the develop- 

 ment of a compact shoot by condensation from a laxly forking rhizome. 

 Similar basal buds are seen in Lophosoria, Metaxya, and Aisophila, though 

 these lie nearer to the leaf-base and are median. Collectively such facts 

 suggest frequent progressions, probably polyphyletic, from a lax creeping 

 rhizome to a compact, and ultimately it may be to a dendroid habit. 



The simple dictyostele oi Dryopteris (Fig. i, E, F), and the insertion of the 

 highly disintegrated leaf-trace upon the lower region of each foliar gap closely 

 resembles what has been seen in Peranema. The general conclusion naturally 

 follows that in external form and in internal structure the two genera are 

 closely related: as also is Diacalpe. This will make the comparison of their 

 sori all the more interesting. 



1 The Male Shield Fern is so familiar an object, even to elementary students, that it is liable to 

 be treated simplj' as a "type," while comparison of its features from an evolutionary point of view 

 is apt to be left in abeyance, chiefly perhaps from deficiency of knowledge of the necessary facts. 

 A like treatment is often meted out to the Bracken. It is seldom realised, even by teachers, and very 

 rarely indeed is it suggested by them to students, that these two common and almost cosmopolitan 

 Ferns occupy distinct and very important positions in the phyletic system. They are alike in the fact 

 that both are intermediate types, and that they have interesting relations both upwards and down- 

 wards in the evolutionary scale. They take their distinct places : the Bracken, with its dermal hairs 

 in the marginal series, being related downwards to the Dicksonioid Ferns in which scales are absent: 

 the Male Shield Fern, with its chaffy scales so prominent a feature, being related downwards to the 

 scaly Cyatheoid Ferns. 



