236 BRYOPHYTA. [CH. 



Berendt^ in their monograph on the amber plants, published in 

 1845. The determinations have since been revised by Gottsche^ 

 who recognises species of Frullania, Jungermannia, and other 

 genera. 



ISPHAGNALES. 

 ANDREAEALES. 

 BRYALES. 



The plant-body (gametophyte) in the Musci consists of a 

 stem bearing thin leaves, usually spirally disposed, rarely in 

 two rows. The internal differentiation of the stem is generally 

 well marked, and in some cases is comparable in complexity 

 w^ith the structure of the higher plants. A protonema arises 

 from the spore, having the form of a branched filamentous, 

 or more rarely a thalloid structure. Reproduction as in the 

 group Bryophyta. 



Mosses like Liverworts have an extremely wide distribution, 

 and occur in various habitats. In many districts vast tracts 

 of country are practically monopolised by peat-forming genera, 

 such as Sphagnum and other Mosses. Some genera are found 

 on rocks at high altitudes in dry regions, a few grow as 

 saprophytes, and many occur either as epiphytes on the leaves 

 and stems of other plants, or carpeting the ground under the 

 shade of forest trees. 



In the simpler Mosses, the stem consists of a parenchy- 

 matous ground-tissue with a few outer layers of thicker-walled 

 and smaller cells. In others there is a distinct central cylinder 

 which occupies the axis of the stem, and consists of long 

 and narrow cells ; in the more complex forms the structure of 

 the axial tissues suggests the central cylinder or stele of higher 

 plants. The genus Polytrichum, so abundant on English moors, 

 illustrates this higher type of stem differentiation. In a 

 transverse section of the stem the peripheral tissue is seen to be 

 composed of thick-walled cells, passing internally into large 

 parenchymatous tissue. The axial part is occupied by a 



1 Goppert and Berendt (45) PI. vi. and (53). 



2 Gottsche (86). 



