BEYOPHYTA 99 



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

 true vessels or tracheids never being found. A similar tissue 

 occurs in the midribs of the 1 eaves in some species. Tlie epidermis 

 is not completely differentiated and bears no stomata. The 

 apical meristem is usually well defined, and consists sometimes 

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



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

 two kinds, antheridia giving rise to antherozoids or spermato- 

 zoids, and archegonia, containing each an oospherc. 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. 



F'nj. 858. Protonema of Moss. A. Early stages of germiuatiou of spore. 

 B. Developed protonema on which young bud, Jc w, 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 investments. The 

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

 with a stalk (figs. 859 and 866). They consist of a wall composed 

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

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

 long cilia and known as a spermatozoid or antherozoid. The 

 cells in which the latter bodies are developed are Itnown as 

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

 the mother cells escape, the spermatozoids being discharged 

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

 number of the latter. 



h2 



