SECT. vn. BRYEI. 329 



ceedingly numerous, and contain the simplest of all 

 mosses ; they grow on newly turned-up soil, and are 

 chiefly annual. Their leaves generally have nerves, and 

 are bordered by large cells. The urns, which are either 

 sessile, or upon a short stalk, have not a trac6 of peri- 

 stome, and sometimes have a columella, sometimes 

 not. The spores are large compared with those of other 

 mosses. 



The tribe Dicranei contains numerous species, some 

 of which are the commonest of mosses in Europe. 

 They are easily known by their single peristome of six- 

 teen teeth divided half-way down. The leaves are ex- 

 tremely crisp and convolute, and the hood is spoon- 

 shaped. The Leucobryum is remarkable for pallid 

 leaves; it has three layers of cells, a narrow layer 

 of green cells embedded in the centre of the leaf with 

 a broader layer of colourless cells on each side, whose 

 cell walls are perforated with large round openings, as 

 in fig. 50 b. The mosses of this order live on sand- 

 stone rocks, shady banks, and trunks of trees. Fig. 50 

 shows the microscopic structure of the leaves of various 

 mosses. 



In the tribe Grimmiei we have frequently a sessile 

 urn, with a single peristome, and a mitre-shaped hood. 

 The leaves, which are dark green, have minute hex- 

 agonal perforated cells on their upper surface, and a 

 white nerve projecting from their extremity. 



In the tribe Polytrichei the mouth of the urn is mostly 

 closed by a flat membrane and a hood rough with silky 

 hairs. The leaves are sheathing at their base and 

 spreading at their tips ; except in a few cases they are 

 rigid; and the nerve often exhibits lamelliform folds. 

 The Polytrichum dendroides contains scalariform ducts, 

 and starch granules. 



The Bryei are of variable size, but a number of 

 European species are among the finest of mosses, on 



