BRYOPHYTA— MUSCI 



113 



Class Y.— MUSCI (MOSSES). 



In the group of the true mosses a still further advance, espe- 

 cially in the direction of anatomical differentiation, is seen. The 

 gametophyte is always foUose, and bears rhizoids instead of 

 simple root hairs. The sporogonium escapes from the calyptra 

 before the spores are mature ; it never contains elaters, and always 

 possesses a well-defined columella. The plants are of small size, 

 and grow upon the earth, rocks, trees, or old walls ; some are 

 saprophytic, growing on decaying wood, &c. A few are aquatic. 



Ficx. 871. 



Fig. 870. Protenema of Moss. A. Early stages of germination of spore. 

 B. Developefl protonema on which young laud, k ic, is formed, which will 

 give rise to the moss plant. After Sachs. 



The protonema is in most cases a filamentous structure, 

 copiously branched. The septa are usually arranged obliquely 

 across the filament. Generally part of it ramifies below the 

 surface of the soil and is colourless, while the remainder con- 

 tains chloroplastids. Each filament grows by segmentation 

 of a single terminal or apical cell. 



The shoot is rarely dorsiventral as in the Liverworts. It grows 

 by means of an apical cell, which is usually three-sided, and 

 gives rise by its segmentation to three rows of leaves. It is 

 frequently branched, the branches arising not in the axils of the 

 leaves, as in the Phanerogams, but either beside or below them. 



VOL. II. I 



