io8 DRYOPTEROID FERNS [ch. 



The vascular anatomy of Peraneina compares closely with that of Dryo- 

 pteris filix-nias. There is a dict}-ostele without perforations, while the highly 

 divided petiolar-trace, composed of 3 to 5 main strands together with 

 some smaller strands, springs outwards from the lower side of the leaf-gap 

 (Fig. 652, 1, II, III). The ground tissue is crowded with nests of sclerenchyma 

 of irregular size and distribution, a feature not uncommon in Ferns which 

 need to resist occasional drought. The structure of the petiole resembles 

 that of the Male Shield Fern, while the origin of the pinna trace is as in 

 Cyathedid types (Fig. 652, iv, v). A single-stalked sorus is shown in section in 

 Fig. 650, G. It arises above one of the lateral veins, but always at some 

 distance from its tip, and the stalk attains a length of about i mm. A median 



/Ay 



Fis^. 652. Pcranema cyatheoides. i = part of dictyostele seen from 

 within, showing the leaf-gap, and strands of leaf-trace passing 

 outwards from it. il=^the same leaf-gap seen from without, m = 

 median strand, a^=:adaxial strands. lli = another leaf-gap with 

 its own leaf-trace sti-ands (/./.), together with parts of the leaf- 

 traces above, right and left {a.a. and b.b.). iv, v= transverse sec- 

 tions of the petiole, showing the origin of the trace of one of the 

 basal pinnae (/); 5 = subsidiary strands. (After Davie. Magnified.) 



section of a sorus still in an immature state is shown in Fig. 653. The stalk is 

 traversed by a vascular strand which dilates in the receptacle into a loose 

 mass of tracheides, as in Dryopteris (Vol. I, Fig. 14). The convex surface of 

 the mature receptacle is covered by a dense mass of sporangia, and the 

 whole is protected by a single-layered indusium, excepting for the narrow 

 opening already mentioned, which lies at the insertion of the stalk, on the 

 side towards the leaf-margin. Here the indusial lip may be curved inwards 

 so as to leave only a narrow well-guarded channel leading to the mass of 

 sporangia within. We have here one of the most accurately protected sori 

 of the whole group. The origin of the sporangia is at first almost simul- 

 taneous, though comparison of numerous sections led Davie to conclude 

 that the succession is at the first essentially basipetal: in any case a mixed 



