HYPNACE^). 387 



occasionally short and wide, always in such cases show a 

 rhomboid or hexagonal outline, and are never regularly oval, 

 rounded, nor quadrate, at least in the middle of the leaf. 



The texture of the leaves is usually thin and membranaceous, 

 often somewhat scariose and glossy ; when dry they rarely 

 become crisped, though sometimes shrinking and becoming 

 flaccid ; as a rule they are little altered when dry and on 

 moistening rapidly regain their normal condition. 



Several of the genera here included with erect, symmetrical 

 capsules are frequently separated under the title of Ortho- 

 theciaceae ; but the distinction cannot be held of real importance, 

 since it leads to the separation of genera so obviously allied as 

 Pleuropus and Camptothecium, and to other anomalies. 



The student will have little difficulty in recognising a moss 

 as a member of this Order if attention be paid to the areolation. 

 Pterogonium, Antitrichia and Leucodon, indeed, have somewhat 

 elongate upper cells, but the marginal cells in the lower part of 

 the leaf, not the angular ones only, are short and rounded; and 

 the inner peristome, too, is more or less imperfect, at least in the 

 two latter. 



In the descriptions of the leaves, when not otherwise stated, 

 those of the secondary stems or their divisions are referred to, 

 not those of the branches ; the branch-leaves being usually 

 narrower and* frequently less highly developed than the stem- 

 leaves. » 



In the arrangement and the division into genera, as well as in 

 the nomenclature, I have for the most part followed the system of 

 the authors of the Bryologia Europsea, and of Schimper in the 

 Synopsis, Ed. II. This arrangement is open to much criticism, 

 both as to nomenclature and to the value of the genera ; it is, for 

 instance, to say the least doubtful whether groups like Pleuropus, 

 Camptothecium, and Brachythecium have any claim to a separate 

 generic rank which puts them on the same level as the genera of 

 Acrocarpous mosses, separated only as they are by characters 

 almost indefinable and none too constant. Lindberg has given an 

 original and very different arrangement in the Musci 

 Scandinavici ; but, besides that some of his grouping appears 

 very difficult to justify, I have thought it better not to run the 

 risk of causing confusion by the introduction of an arrangement 

 and nomenclature so widely differing from that of most of the 

 works the student is likely to consult, and have therefore kept 

 more or less closely to the old lines. The chief variation will be 



