BBYOPHYTA 



99 



tissue occuping the centre. This is, however, very rudimentary, 

 true vessels or tracheids never being found. A similar tissue 

 occm's in the midribs of the leaves in some species. The epidermis 

 is not completely differentiated and bears no stomata. The 

 apical meristem is usually well defined, and consists sometimes 

 of a single apical cell and sometimes of a group of such cells. 



The sexual organs, borne only on tlie gametophyte, are of 

 two kinds, antlieridia giving rise to antherozoids or sjjennato- 

 zoids, and archegonia, contaming each an oosi:ilierc. In most 

 cases they arise in groups, often on special receptacles, or at the 

 apices of leafy shoots. They are generally surrounded by some 



Fig. 858. 



Fi'j. 858. Protonema of Moss. A. Early stages of geraiiuatiou of spore. 

 B. Developed protonema on which young bud, k u; is formed, which will 

 give rise to the moss plant. After Sachs. 



arrangement for protection, being either embedded in the tissue 

 of the receptacle or furnished with foliaceous mvestments. The 

 antlieridia are club-shaped, spherical, or ovoid bodies, furnished 

 with a stalls { figs. 859 and 866). They consist of a wall composed 

 of a single layer of cells, and a mass of cells in the mterior, each 

 of wliich gives rise to a spirally coiled body furnished with two 

 long cilia and known as a spermatozoid or antherozoid. The 

 cells m which the latter bodies are developed are known as 

 mother cells. When the antheridium is mature it bursts, and 

 tlie mother cells escape, the spermatozoids being discharged 

 from them later {fig. 860, a). Each antheridium produces a large 

 number of the latter. 



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