mnium. 347 



at base larger, sub-rectangular. Capsules sometimes aggregate, 

 horizontal, yellowish brown, finally brown, lid with a rather stout 

 shortly rostrate beak, usually decurved ; peristome deep yellow, 

 finally brownish. Synoicous. 



Hab. Rocks, usually by streams ; not common. Fr. spring. 



M. serratum is a plant of alpine and subalpine regions, while M. hornum, though 

 equally at home there, is more frequently found in lowland woods. The characters- 

 separating the two plants will be found under the latter species. 



Mnium serratum is often quite indistinguishable in the field from M. ortho- 

 rrhynchum, although the latter is usually somewhat more densely tufted with the leaves, 

 more crowded. Under the microscope the difference is easily seen, the cells in M. 

 serratum being internally rounded, not angular, and half as large again in diameter as 

 those of M. orthorrhynchum. M. riparium differs in its usually smaller size, more 

 distant leaves, and dioicous inflorescence. 



7. Mnium orthorrhynchum B. & S. (Tab. XLVII. B.). 



Allied to the last species, but more closely tufted, with the 

 leaves in the upper part of the stem and branches more closely 

 set, narrower, oblong-lanceolate, doubly spinose-serrate from 

 below the middle ; cells often but not always seriate, angular, 

 quadrate or hexagonal, small, about 75 p in diameter, chloro- 

 phyllose, incrassate. Seta about an inch long, red, solid, solitary ;: 

 capsule usually horizontal, oblong ; lid shortly rostrate, straight 

 or oblique. Dioicous. Male flower discoid. 



Hab. Rocks, especially in damp situations in mountainous country. Rare. 

 Fruit very rare, late summer. 



In its aspect this species usually resembles a slender form of M. hornum, and is 

 in this way often distinguishable from M. serratum, but by no means always. The 

 dioicous inflorescence and the small angular cells are the safest guides. 



Several allied plants have been described as species from the continent and from 

 N. America, some of which will no doubt stand ; one of these (M. lycopodioides 

 Hook. ) should be looked for here. It is well described by Philibert in the Rev. Bry. 

 1895, pp. 2 sqq. It differs in the more distant, more laxly areolated leaves toothed to- 

 near the base, as well as in the fruit ; it is in fact more nearly allied to M. riparium. 



8. Mnium riparium Mitt. (Tab. XLVII. C). 



Closely resembling M. serratum, but with more distant 

 broader leaves, usually more quickly narrowed at the base, 

 ovate-oblong ; on the sterile shoots often rounded-ovate ; cells 

 resembling those of M. serratum, about 20 /j, in diameter, 

 rounded, hardly angular . Seta short, pale red; capsule horizontal 

 .or sub-pendulous. Dioicous. 



Hab. Shady woods and rocks by water, very rare. Sussex ; Yorkshire ; 

 Perthshire. Fruit not found in Britain, spring. 



