92 THE BIOLOGY OF A PLANT. 



and matured in the following manner : A superficial (epidermal) 

 cell enlarges and becomes divided into a proximal (basal) cell 

 and a distal (apical) cell (Fig. 53, a). The former develops 

 into the future pedicel or stalk of the sporangium ; the latter gives 

 rise to the head or capsule within which the spores are formed 

 (cf. Fig. 51). The pedicel arises from the original pedicel-cell 

 by continued growth and subdivision until it consists oi three 

 rows of cells somewhat elongated. The rounded capsule-cell 

 is next transformed by four successive oblique divisions into 

 four plano-convex " parietal cells" and a tetraheclral central 

 cell, the archesporium, enclosed by the others. The capsule- 

 cell is thus divided by three planes inclined at about 120 

 (Fig. 53, 5, <?). A fourth (Fig. 53, d, e) passes nearly parallel to 

 the top of the capsule and cuts off from it the central cell 

 or archesporium. In the parietal cells further divisions fol- 

 low, perpendicular to the surface, while the archesporium gives 

 rise to four intermediate or tapetal cells, parallel to the orig- 

 inal parietal group (Fig. 53, g). The sporangium now con- 

 sists of a central tetraheclral archesporium bounded by four tape- 

 tal cells, which in turn are enclosed by the parietal cells, at this 

 time rapidly multiplying by divisions perpendicular to the ex- 

 terior. Owing to the peculiar position of the planes of division 

 the whole capsule is now somewhat flattened, and it becomes 

 still more so by the formation along the edge, of a peculiar 

 structure called the ring or annulus, whose function is the rup- 

 turing of the capsule and the liberation of the spores. The an- 

 nulus is formed by a number of parallel transverse partitions (Fig. 

 53,y, h, i,j), which subdivide the peripheral cells of one edge of 

 the capsule until a certain number of cells have been formed. 

 These then project upon the capsule (Fig. 53, j) and form an in- 

 complete ring (Fig. 53, &). 



Meanwhile the tapetal cells sometimes subdivide so as to 

 form a double row (Fig. 53, A), and soon afterwards are absorbed, 

 space being thus left for the growth and enlargement of the 

 archesporium. The latter now divides first into 2, then into 4, 8, 

 and finally 16 cells, the mother-cells of the spores. These remain 

 for a time closely united, but eventually separate and again 

 subdivide, each into 4 daughter-cells (Fig. 53, I). The 64 cells 

 thus formed are the asexual spores. In their mature state they 

 have a tetrahcdral form and certain external markings indicated 



