84 A TEXT-BOOK OF BOTANY. 



it develops chlorophyll and possesses stomata resembling those 

 found in certain groups of mosses and higher plants. 



MUSCI. 



In the Bosses the archegonia always form the end of the 

 axis of a shoot, whether this be a main one or a lateral one. As 

 has already been stated (p. 78), the sexual organs are surrounded 

 by leaves or leaf-like structures, known as perichsetia or peri- 

 chaetal leaves, and by hair-like structures or paraphyses, both of 

 which are considered to act as protective organs. Sometimes 

 the groups of sexual organs together with the protective organs are 

 spoken of as the " moss flower." As already stated, the Mosses 

 are both monoecious (Fig. 49, C, D) and dioecious (Fig. 49, A, 

 B), hence a moss flower may contain only one of the sexual organs 

 or it may contain both. Mosses are also characterized by an 

 abundant vegetative propagation. New branches are developed 

 from the old. " Almost every living cell of a moss can grow out 

 into protonema, and many produce gemmae of the most different 

 kinds." Entire shoots provided with reserve material are cut 

 off and form new plants. In this way moss carpets are frequently 

 formed in the woods, or masses in bogs. 



Moss Groups. There are two general classes of mosses : ( I ) 

 SPHAGNUM forms are those which produce leaves without nerves, 

 and in which the sporogonium does not possess a long stalk or 

 seta. What appears to be the stalk is the prolongation of the 

 gametophyte stem which is known as the pseudodium or " false 

 stalk." These forms are characteristic of wet places. Some of 

 the group, as Sphagnum proper, form " sphagnum bogs." New 

 plants develop on top of the old, which latter gradually die and 

 finally pass into sphagnum peat, which forms thick masses and 

 finds use as a fuel. (2) The TRUE MOSSES are especially distin- 

 guished by the differentiated character of the sporogonium, which 

 not only produces a stalk but also the peristome (Fig. 45, />), 

 which when present is of great importance in distinguishing the 

 different species. 



Economic Uses of Bryophytes. The investigations on the 

 chemistry of the Liverworts and Mosses have not been very 

 numerous. The constituents which have been found are in the 



