98 MOSSES AND FERNS chap. 



side turned toward the ventral surface of the plant. From this 

 cell three sets of lateral segments are cut off, two dorsal and 

 one ventral, and each of these gives rise to a row of leaves, a 

 leaf corresponding to each segment of the apical cell. The 

 first division wall in each segment is at right angles to its 

 broad faces and divides it into two cells of somewhat unequal 

 size. The next wall formed divides the larger of the two 

 primary cells into an inner and an outer cell (Fig. 42, A), so that 

 the young segment now consists of three cells, an inner one 

 and two outer ; the latter in the dorsal segments correspond to 

 the two lobes usually found in the dorsal leaves. The two outer 

 cells now divide by walls in two planes, and rapidly grow out 

 above the level of the apical cell and form lamellae which re- 

 main single-layered, and undergo but little further modification 

 beyond an increase in size. From the base of the young leaves 

 simple hairs develop, but remain small and inconspicuous. The 

 inner of the three first formed cells of the segment, by further 

 division and growth in all directions, produces the axis of the 

 plant. This in cross or longitudinal section shows almost 

 perfectly uniform tissue. No distinct epidermis, or central 

 strand, like that found in most Mosses, can be seen. 



The branching is monopodial and the branch represents 

 the ventral lobe of a leaf. After the first division by which 

 the two lobes of the leaf are separated, only the dorsal one 

 develops into the lamina of the leaf, which is thus in the 

 segment from which a branch is to form, only one-lobed. In 

 the ventral cell three walls arise (Fig. 43), intersecting so as 

 to cut out a pyramidal cell of the same form as the apical cell 

 of the main axis, and the cell so formed at once begins to 

 divide in the same way, and forms a lateral axis of precisely 

 the same structure as the main one. 



The plants are strictly dioecious and the two sexes are at 

 once recognisable. The males are smaller, and bear special 

 lateral branches which project nearly at right angles from the 

 main axis, and whose closely imbricated light green leaves 

 make them conspicuous. At the base of each of the leaves is 

 a long-stalked antheridium, large enough to be readily seen 

 with the naked eye. 



The development of the antheridium may be easily traced 

 by means of sections made parallel to the surface of the 

 branch. At the apex (Fig. 42, C) is an apical cell much 



