^s- 



DRYOPTEROID FERNS 



[CH. 



ex-indusiate Ferns of Goniopterid-habit, with relatively large leaf-expanses: 

 they differed from Gcniopteris only by their less highly divided leaves, and 

 by their elongated or confluent sori. There is in fact a consecutive sequence 

 of forms leading onwards from the section Lastraea (Diels, I.e. p. 177). The 

 characteristic Goniopterid venation is seen in Fig. 6^1, A. The sori are 

 usually roundish, and are seated at the junction of two secondary veins that 

 meet at an acute angle. They may be compared with those of ex-indusiate 

 Dryopteroids. But sometimes the sori are seen to be elongated following the 

 course of the veins, while in others the whole under surface of the leaf may 

 be covered by sporangia. In fact a progression is illustrated towards an 

 Acrostichoid state. 



It is but a step from this to the condition seen in certain pinnate species 

 oi Leptochiliis, a genus formerly included in Acrostichiun {Syn. Fil. p. 417). 

 Their general habit is that of Meniscmm, and comparison of their venation 

 shows that it is of the same type, but with greater complication of its net- 



Fig. 663. Venation o{ Dryopteris and Leptochiliis. A=D. lu-ophylia [Meniscmm). B = 

 L. siibcrenatiis. C= L. scalptiiratus. D = L. heteroclitiis, sterile. £ = L. keterocliCus, iextils. 

 ( X about 2. After Frau Eva Schumann.) 



work (Fig. 663, B-E). The spores have a perispore, as in Dryopteris. Frau 

 Eva Schumann has examined the relation of the sporangia to the veins, 

 both in normal and in half-fertile leaves. In the latter they are seated chiefly 

 along the veins, or in their near proximity (Fig. 664). Where a normal 

 sporophyll has been cut through in an early stage, the oldest sporangia are 

 .seated above the veins: but younger sporangia cover the intervening surfaces, 

 showing a completely Acrostichoid state (Fig. 665). The facts are here so 

 cogent that it may be stated definitely that such pinnate species oi Leptochiliis 

 as L. ciispidatiis (Pr.) C. Chr. are to be held as Dryopteroid derivatives, and 

 that their Acrostichoid condition has been derived from ex-indusiate types 

 such as the old genus Meniscmm, the sori having spread along the veins 

 and finally over the whole lower surface of the sporophyll. 



Sequences of events distinct from this, and from one another, lead to the 

 condition seen in Polybotrya Willd. and in Stenosejnia Presl. We may start in 

 each case from a soral but ex-indusiate and heterophyllous type of Dryo- 

 pteroid. In Polybotrya it has been shown by Frau Eva Schumann how the 



