16 HANDBOOK OF BRITISH MOSSES. 



num, as frequently eroded, though they never assume the ex* 

 centric outline which is so common amongst Jungermannia. 

 An approach however is made in Homalia trichomanoides 

 (Plate 4, fig. 5) and in Schistostega osmundacea (Plate 14, 

 fig. 4). 



In several cases the lamina, beyond the nerve or between 

 the nerve and the margin, consists of more than one stratum 

 of cells, as for example in Leucobryum glaucum (Plate 1, fig. 6), 

 where the green cells are imbedded between two strata of 

 white cells, whose walls are perforated, while in Sphagnum 

 (Plate 1, fig. 5) the large perforated cells which contain a 

 spiral thread have uniformly a border of narrow distinct green 

 cells. 



The border of the leaf is often revolute, and sometimes in- 

 volute, and the base variously amplexicaul. The whole leaf 

 is sometimes convolute. In every case the leaves are sessile, 

 and they are never deciduous. In some instances, as in Fonti- 

 nalis (Plate 3, fig. 2), they are so closely folded that they are 

 strongly keeled, and eventually split along the keel, so that 

 each leaf looks as if it were double, a circumstance which has 

 occasionally led to error. 



Their direction is extremely variable. They are often 

 crowded and imbricated, frequently however they are patent, 

 not unfrequently secund, while many instances occur in which, 

 either wholly or in part, they are remarkably squarrose. In 

 the species with flattened branches they are for the most part 

 really or apparently distichous. In a dry state their direction 

 is often different and sometimes distinctly spiral, while their 

 surface becomes crisped, folded, or undulate. 



They are always arranged round the axis in some definite 

 order. Sometimes they are two-ranked with the stem still 

 cylindrical or flattened, sometimes three-ranked, but more 



