232 ORTHOTRICHACE.S. 



SUB-GROUP II. DIPLOLEPIDEM. 



Peristome normally double, occasionally single, rarely 

 wanting. When present each outer tooth consists of two layers 

 of plates, the outer layer of two series divided by a vertical line, 

 the inner of a single series extending across the width of the 

 tooth, which, therefore, when viewed from the dorsal or exterior 

 surface, presents a dividing line down the centre ; the ventral or 

 interior surface, on the other hand, being without this division. 

 The inner peristome when present is usually composed of thinner 

 and more delicate tissue, consisting of two thin layers of plates, 

 the external layer divided by 16 vertical lines, alternating with 

 the outer teeth, the internal variously divided. 



This Sub-Group contains by far the greatest number of the 

 mosses, including the whole of the pleurocarpous species, and 

 some of the most extensive Orders of the acrocarpous ones. 

 Philibert has shown that the single peristome of the Aplolepideas 

 is the homologue not of the outer but of the inner peristome of 

 the Diplolepideae. It is therefore misleading to speak of the 

 outer layer of teeth in the latter as the peristome and the inner as 

 the endostome, a term occasionally used ; it would indeed be more 

 in accordance with the actual facts to term the latter the 

 peristome and the outer layer the exostome. 



* Diplolepideae Acrocarpx. 



Acrocarpous mosses, as in the preceding Orders, with a few 

 rare exceptions. Stems erect, very rarely prostrate, branching 

 frequently dichotomous. 



In Anoectangium the fruit is truly pleurocarpous, but the 

 plant is erect, the stems dichotomously branched, and the general 

 habit quite that of the acrocarpous mosses. 



Order XI. ORTHOTRICHACEyE. 



Plants usually growing in short dense cushions ; stems 

 dichotomously branched. Leaves oblong-lanceolate or linear- 

 lanceolate, usually very hygroscopic ; cells more or less rounded- 

 hexagonal, frequently papillose. Seta erect, often very short, 

 capsule exserted or more frequently more or less immersed ; 

 erect, symmetrical, smooth or striate. Calyptra smooth and 

 cucullate, or campanulate and plicate, often with erect hairs. 

 Peristome double or single, rarely none ; the outer teeth 

 frequently united in pairs. Growing on rocks or the bark of trees. 



