I30 



DRYOPTEROID FERNS 



[CH. 



D. phegopteris. But the distinction is bridged over by many tropical species 

 leading from the indusiate to the ex-indusiate state. In the latter a tendency 

 commonly appears to extend the sorus along the course of the vein that 

 bears it: this is to be seen in the Beech Fern (Fig. 66i, y4), but more markedly 

 in Dryopteris decussata (L.) Urban (Fig. 66 1, E). Such details are reminiscent 

 of a like spread of the sorus in Hypolepis rcpe)is (Figs. 586, 587, pp. 9, 10), 

 which, however, belongs to a quite distinct phylum. In both we see a feature 

 frequent in the more advanced phyletic types, viz. the discarding of structures 

 protective of the sporangia, followed by a loosening of control of the sorus. 

 In earlier days these would all have been swept into the comprehensive but 

 heterogeneous genus Polypodiinn : now the examples quoted take their places 

 respectively as Dryopteroid and Dennstaedtioid derivatives. 

 A 



Fig. 661. y4 = Dryopteris phegopteris (L.) C. Chr. A segment of the second order, showing the naked 

 sori elongated along the veins ( x 5). After Luerssen. B = Dryopterts decussata (L.) Urban, part of 

 a pinna, enlarged, after Mettenius, from Christ. 



ACROPHORUS Presl 

 Presl's monotypic East Indian genus AcropJiorus appears to find its natural 

 place here. It has been referred to a Davallioid affinity: but its habit, its 

 anatomy, and the presence of plentiful chaffy scales all point towards 

 Dryopteris. The upright stock contains a simple dictyostele with highly 

 segregated leaf-traces, after the type of the Male Shield Fern. The sorus is 

 sometimes seated on the end of a vein, hence the generic name. This is seen 

 in Fig. 662, rt, which also shows the small fimbriated indusium. But often it 

 may be attached laterally on the vein which extends beyond the receptacle, 

 as in Fig. 662, b: both types may appear upon the same leaf. The indusium 

 is very variable, and it is often so small as to be hidden by the sporangia 

 when mature. The sorus is of the mixed type. All this points to an affinity 

 of Acrophoriis with Dryopteris. The similarities that led to a reference to the 

 Davallieae are probably homoplastic, and they are negatived by the anatom}% 

 and by the presence of chaffy dermal scales. 



