FERNS— FRUCTIFICATIONS 287 



cells, which also extends for some distance along 

 the outer side of the sac (Fig. 109, D, b, d). The 

 annulus is accompanied by multicellular hairs. 



The leaf was a thick fleshy one, with a layer of 

 palisade-cells, but the most characteristic anatomical 

 peculiarity is the horse-shoe bundle of the midrib 

 (Fig. 109, D, a). Authorities differ as to the systematic 

 position to be assigned to this curious Fern. Stur, 

 relying on the characters of the sorus, places it among 

 Marattiaceae, near Asterotheca and Scolecopteris, while 

 Zeiller rejects this attribution, on account of the 

 well-marked annulus. The latter feature suggests a 

 comparison with Schizaeaceae or Osmundaceae, but 

 Zeiller leaves the position of the genus an open 

 question. On the whole, the balance of characters 

 seems to weigh on the side of Marattiaceae, for there 

 is no reason why the annulus, still represented at the 

 present time in Angiopleris, should not have been more 

 highly developed in some Palaeozoic members of the 

 family. A relation, through Corynepteris, to the Botryo- 

 pterideae is also possible (see next chapter, pp. 323, 344). 



This brings us to yet another genus, Senftenbergia, 

 of still more dubious affinities. Several species have 

 been included under this genus, the foliage of which 

 was of the Pecopteroid type. The sporangia are 

 inserted singly over the lateral nerves of the pinnules, 

 near their outer end, so as to form a marginal series. 

 There is thus no formation of synangia, or even of definite 

 sori (see Fig. 1 09, G). In the typical species there is a 

 definite apical annulus, several cells in width. Pecopteris 

 exigua, referred to Senftenbergia by Stur, has no annulus, 

 and appears to be a Crossotheca (see Chapter X.). The 



