Il8 FISSIDENTACE^. 



Order VII. FISSIDENTACE.E. 



Plants with truly distichous, vertically placed leaves, in one 

 plane ; in all the British species more or less oblong-lanceolate, and 

 equitant or clasping the stem, the basal part of the upper side of 

 the limb being as it were split to the nerve into two laminae ; the 

 cells hexagonal or rounded. Fruit lateral or terminal, exserted, 

 small, peristome dicranoid. 



The plants of this Order belong with one or two exceptions 

 to the large genus Fissidens, — Conomitrium and Octodiceras being 

 by many authors considered as sub-genera — and, although very 

 variable in size, possess a uniform habit by which they are readily 

 known, and indeed form one of the most natural of the Orders of 

 mosses. 



28. FISSIDENS Hedw. 



The diagnosis given above includes the most important 

 characters of the genus ; to this it may be added that the fruit 

 somewhat resembles that of Dicranella, but is always smooth, not 

 striate ; the peristome is usually very densely and highly papillose, 

 the papilla? often tending to take a spiral arrangement, instead 

 of being in vertical lines, and the divisions are subulate, straighter 

 and more rigid than is usual in Dicranum. 



The position of the male inflorescence is exceedingly variable, 

 and in the descriptions as well as in the arrangement of the species 

 I have paid little heed to this character. 



The synonymy of the various species, especially of the more 

 minute ones, is exceedingly involved and complicated ; I have for 

 the most part followed Braithwaite in his original nomenclature 

 (Brit. M. Fl., Vol. I., pp. 67-80), as being on the whole the most 

 rational. I have used almost the same terms as Braithwaite in 

 designating the different parts of the leaf, indicating by ' sheathing 

 laminse ' the conduplicate portion, by ' superior lamina ' the part of 

 the leaf beyond the sheathing laminae on the upper side of the 

 nerve, by ' inferior lamina ' the whole of the lamina on the lower 

 side of the nerve. The nerve itself will in most of the species be 

 found to reach just to the apex, where it often becomes confluent 

 with the cells of the thickened border when that is present. 



The calyptra is small and cucullate, but occasionally it may be 

 mitriform, and more rarely quite entire at the base ; but these 

 differences do not appear to mark any important divergence of 

 types. The areolation of the lowest leaves on the stem is usually 

 laxer than that of the upper ones. 



