HYPNUM. 459 



hardly reaching half-way ; cells very short, 4-5 times as long as 

 wide, sub-hexagonal ; auricles less distinct. 



Hab. Marshes, pools, etc. Common. The var. Kheiffii common. The var. 

 gracilescens rare. Fr. very rare, summer. 



This is an exceedingly protean species, and the characters given above, especially 

 as regards the measurements of the cells, must be looked upon as approximate only. 

 The variations are endless, in form of leaf, length of cells, size, mode of branching, 

 etc., and innumerable varieties have been described, many of those described by one 

 author being doubtless almost identical with those of another, according as one set 

 of characters or another is chosen for a basis of classification. Some forms are 

 exceedingly slender, with short, wide, hardly falcate leaves ; approaching H. riparium 

 in many respects ; others are very like H. fluitans, often being aquatic, elongated, 

 soft, regularly pinnate with long spreading leaves, giving a very plumose aspect to the 

 plant. The var. Kneijfii, often separated as a species, is one of the most distinct, 

 but many intermediate forms occur, and the differences are rather of habit than of 

 structural importance. An extremely slender, golden green plant which I gathered 

 on damp sand hills in Donegal Co., with minute short leaves, the nerve short, faint 

 and sometimes almost wanting, and very short wide cells, appears to belong to the 

 var. gracilescens Schp. (forma gracilescens Ren.), but it may possibly be more 

 accurately referred to the var. tenue Schp. , between which and the var. gracilescens 

 there is, as admitted by Schimper, very little difference. 



In spite of its great variability, H. aduncum is rarely difficult to distinguish from 

 the allied species, except from H. fluitans, which may almost always be known by 

 the narrower leaves, denticulate at base, with very narrow cells remaining almost 

 uniform to the base, and with a longer nerve ; there are, however, forms which are 

 extremely hard to separate. H. Sendlneri is more robust, with the leaves more 

 strongly falcate, the nerve stronger and cells firmer and narrower. H. vemicosum 

 has the leaves more falcate, plicate, and without decurrent auricles ; H. revolvens and 

 H. Cossoni are distinguished by similar characters, though the leaves are not plicate. 



8. Hypnum Sendtneri Schp. (Amblystegium Sendtneri 

 Lindb.) (Tab. LVII. A.). 



Typically rather slender, resembling H . vemicosum ; stems 

 erect, divided, with few branches, 3-6 inches high ; leaves 

 crowded, \-\ line long, strongly falcato-secund, almost circinate, 

 strongly hooked at the tips of the stems and branches, somewhat 

 flexuose and twisted when dry, more glossy than in H. aduncum, 

 which they resemble in structure; not plicate, entire; nerve 

 strong, wider than in H. aduncum, about 60-100 /* wide at base 

 (in H. aduncum 50-60 /*), usually extending into the acumen ; 

 cells about equal to those of H . aduncum in length, but narrower 

 with firmer walls, linear-flexuose, obtuse, almost uniform to base, 

 the basal usually with thin, not porose walls, the angular cells 

 firmer, with somewhat thick walls, less hyaline, forming distinct 

 decurrent auricles. Capsule longer than in H. aduncum, sub- 

 cylindric, suberect. DioiCous. 



Hab. Bogs, marshes, etc., not common. Fr. rare, summer. 



