100 HISTORY OF BRITISH FERNS. 



cognized at a glance. The mark by which it is known is 

 this : the back of every frond is covered by densely- 

 packed, brown, pointed, chaffy scales. Among these scales, 

 and concealed by them, lie the elongate sori, which are 

 anomalous, in regard to their relationship, in having no 

 indusium. The affinity of Ceterach is without doubt with the 

 Asplenium-like Perns, and this being the case they ought 

 to have an indusium ; the Polypody-like and Acrostichum- 

 like Perns only, among the dorsal groups, wanting this 

 cover to the sori. No indusium, however, exists here, 

 unless it be represented by a kind of membranous ridge, 

 which exists on the receptacles just behind the sori, and is 

 the part which has been called an indusium. The proba- 

 bility is, that it does represent that organ, which is not 

 largely developed in consequence of the presence of so 

 dense a covering of scales, these not only serving the pur- 

 pose of a cover to the sori, but perhaps, from their crowded 

 position, preventing its proper formation. 



The name Ceterack is an alteration of the word Chetkerak, 

 which was applied to this plant by Persian and Arabian 

 medical writers. 



CETERACH OFFICINARUM, Willdenow. The Scaly Spleen- 

 wort. (Plate I. fig. 1.) 



