CHARACTERS OF TRIBES AND GENERA. 337 



section Hemidictyum, along with the two species of Aspleni- 

 dictyum and Hemidictymn marginatum, all three very dis- 

 tinct in habit. Although I now place Ceterach after Hemi- 

 dictyum it is not that I consider it has any relationship, 

 but merely on account of having no ally for it, I place it 

 as an anomalous genus at the end of the tribe. 



Sp. C. officinarum, Willd. (v v.) (Grammitis, Sw. ; Scolo- 

 pendrium, Sin.). 



OBS. Found in rocky places, and on old walls in this 

 country, and throughout Europe and the temperate regions 

 of the Northern hemisphere generally. In Madeira the 

 fronds attain a large size, and which by some authors has 

 been described as a distinct species under the name of 

 C. aureum. 



B. Ring of Sporangia horizontal, central. 

 Sect. 1. Sori discal, punctiform, naked, rarely indusiale. 



Tribe 24. GLEICHENE^. (Plate 24). 

 (Gleicheniacece, E. Br.) 



OBS. This Tribe includes a peculiar group of Ferns, 

 consisting of about thirty described species, technically 

 distinguished from Polypodiacece by the sporangia being 

 surrounded with a horizontal ring* generally at right 

 angles with the axis of attachment. This direction of the 

 ring is common to the whole of true Gleiclieniaccce, but in 

 Matonia it is partially oblique. 



Independent of the structure of the sporangia, Gleiclie- 

 niacece are readily known from all other Ferns by their 

 fronds being once or many times dichotomously branched 

 or flabelliform (two species excepted, which have simple 

 fronds). 



