360 PAET III. THE CLASSIFICATION OF PLANTS. 



The gametophyte of the Musci possesses a remarkable capacity 

 for vegetative propagation. Thus the perennial protonema of many 

 species serves year by year to produce new adult shoots which, not 

 unfrequently, become distinct plants. In the pleurocarpous forms 

 (e.g. Sphagnum, Hypnum) the main axes gradually die away from 

 behind, the lateral branches becoming isolated, and constituting 

 the main axes of new plants. In probably the majority of the 

 Musci almost any portion of the body, a piece of stem or a leaf, 

 will, under proper conditions, grow out into protonemal filaments, 

 which give rise to adult shoots in the usual manner. In certain 

 species, belonging to the Bryinese (A.ulacomnium palustre, A. andro- 

 gynum, Tetraphis pellucida], multicellular gemmae are produced at 

 the apex of the stem, either free or enclosed in a cupule (Tetra- 

 phis). In Aulacomnium palustre the gemmae appear to be modified 

 leaves ; in A. androgynum and in Tetraphis the gemmae are 

 smaller, and consist of but few cells ; in Tetraphis they are borne 

 on long stalks. On being placed under favourable conditions, the 

 cells of the gemma grow out into protonema. 



B. The SPOROPHYTE. The oospore divides into two by a wall 

 (basal wall) transverse to the long axis of the archegonium : from 

 the epibasal half is developed the capsule (theca) and its long or 

 short stalk (seta), whilst the hypobasal half gives rise to a more or 

 less well-developed foot : the whole being termed the sporogonium. 



The segmentation of the oospore into octants (see p. 329) is 

 confined to the epibasal cell, and even this can only be traced in 

 Sphagnum, which in this respect resembles the Liverworts. In 

 the other Mosses, the epibasal cell undergoes one or more trans- 

 verse divisions, after which two oblique walls, cutting each other 

 at an acute angle, are formed in the terminal cell ; the cell marked 

 out by these two oblique walls is a two-sided apical cell by the 

 growth and segmentation of which the further development of 

 the embryo is effected. 



At an early stage in the differentiation of the capsule (see Fig. 

 238 B) the amphithecium, consisting of one or more layers of cells, 

 can be distinguished from the endothecium. The amphithecium 

 constitutes eventually the wall of the capsule ; the internal tissues 

 being formed for the most part from the endothecium. 



The archesporium becomes differentiated in various positions 

 within the young capsule. It is differentiated, in the Sphagnaceae, 

 from the innermost layer of the amphithecium ; in the Andreaeaceae 

 and Bryineae, from the external layer of the endothecium : in 



