466 



VASCULAR CRYPTOGAMS. 



Hegelmaier and Russow have confirmed and extended the observation. They are 

 developed from a small group of epidermal cells, as Goebel has shown, and, in con- 

 sequence of repeated divisions, they soon appear as flat projections occupying the 

 whole breadth of the base of the leaf, consisting of a group of internal cells covered 

 by an external layer. Tangential divisions take place in the epidermal cells by means 

 of which the wall becomes two-layered, and the upper or external portion of the 

 tapetum is formed, the tapetum being completed by similar divisions taking place in 



Fig. 327. — A dichotomoiisly branched fertile shoot oi Lycopoditun Chaniiecyparissus, in longfitudinal section, shghtly magnified; 

 yy the axial fibrovascular mass, bb leaves, ss the young sporangia. 



more deeply placed cells : the archesporium probably consists of a transverse row of 

 cells; these undergo division and form a rounded mass of spore-mother-cells. 

 These cells become isolated, their walls undergo considerable thickening, and, after an 

 indicated division into two they form four chambers (the so-called ' special mother- 

 cells '), within each of which the contained protoplasm surrounds itself with a 

 permanent spore-wall. It is not until the projections, spines, &c., have been 

 developed upon this wall that the walls of the chambers of the mother-cells are 

 absorbed. 



