540 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



in the midst. In Antigraimma the veinlets are reticulate, 

 but the twin sori still face each other ; in Camftosorus, how- 

 ever, the sori diverge. Scolopendrium officinarum is one of 

 our most common ferns and rather variable. The frond is 

 sometimes forked, and sometimes the margin is curiously- 

 waved and crisped. One or two other species of the section, 

 as Camptosorus rhizophyllum, belong also to temperate 

 climates. 



614 The second section, which is tropical, in India and 

 America, consists of genera allied to Diplazium. In this the 

 sori are bilateral or double, so that the indusia open in oppo- 

 site directions. With the double sori are often intermixed 

 perfectly simple individuals. Those with simple sori, it is said, 

 may be distinguished from Asjyleniwm by the circumstance of 

 their opening towards the main nerve, while in Diplazium 

 they open from it. I fear, however, that this character is not 

 constant. Anisogonium differs from BiplaziuTH in the 

 return of the pinnate veinlets to the main veins, so as to form 

 little arches. Oxygonium has entire pinnas, with fascicles of 

 veinlets anastomosing near the margin, and there producing 

 free veinlets. Callipteris has costaform veins, the lower 

 opposite veinlets anastomosing so as to form an angle, and the 

 upper free. 



615. The third section contains the large genus Aapjlenium, 

 and one or two genera which have been separated from it. All 

 have pinnate veins, and the sori, whether more or less linear, 

 are attached to the back of a simple vein or the primary fork 

 of the vein, or indiscriminately. The edge of the indusium is 

 sometimes ciliated. In Neottopteris the tips of the veinlets 

 are joined by a transverse continuous anastomosing veinlet. 

 Allantodia has a vaulted sausage-like indusium, with reticu- 

 lated veinlets. Ceterach, as observed before, has no indusium. 

 Hemidictyon is distinguished by " the exterior margin of the 

 reticulated venation being combined by a continuous vein 

 parallel with and close to the margin, and also by its plane 

 indusium." Plenasiwm is the mere barren frond of Osmunda 

 Javanica. Like many large genera, Asplenium has repre- 

 sentatives in most parts of the world, and some of these very 



