GROUPS OF PLANTS. 55 



ferent kinds." Entire shoots provided with reserve material are 

 cut off and form new plants. In this way moss carpets are fre- 

 quently 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 pseudopodium 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 dis- 

 tinguished by the differentiated character of the sporogonium, 

 which not only produces a stalk but also the peristome (Fig. 28, 

 p) 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 

 nature of tannin, resins, ethereal oils, glucosides, alkaloids, color- 

 ing compounds and organic acids like citric, oxalic, tartaric and 

 aconitic. In the mosses starch and silicon salts are found 

 in addition. Several species of Marchantia and Jungermannia ' 

 are used in medicine. Of the mosses the following have been 

 found to have medicinal properties ; Sphagnum cuspidatum, 

 Grimmia pulvinata, Funaria hygrometrica, Fontinalis anfipyre- 

 tica, and several species of Polytrichum and Hypniim. 



PTERIDOPHYTES. 



The Pteridophytes constitute the second subdivision of the 

 Archegoniates. Like the Bryophytes these plants show a distinct 

 alternation of generations, i.e., the gametophyte or sexual gen- 

 eration alternates with the sporophyte or asexual generation. 

 Their relation is, however, somewhat changed. In the Bryophytes 

 the gametophyte is the most conspicuous and is looked upon 

 as constituting the plant proper, whereas in the Pteridophytes 



