FILICmE.'E LEPTOSPORANGIA T.E 



327 



formation of the young stoma is preceded by the formation of 

 a preHminary cell (Fig. 164, v), horse-shoe shaped, and cutting 

 off a small cell from one corner of an epidermal cell. A similar 

 wall forms within this small cell, parallel to the first one (Fig. 

 164, B, St), and the cell thus separated is the stoma mother cell. 

 A longitudinal wall next divides this, and then splits in the 

 middle to form the pore of the stoma (Fig. 164, C). This when 

 complete is exactly in structure like that of other vascular 



Fig. 164. — Atiian/mii ciiiafgiiiatwn (Bory). Development of the stomata, X525 ; v, accessory cell ; 



st, stoma mother cell. 



plants, and like them communicates with the air-spaces of the 

 mesophyll. The accessory cell enlarges very much with the 

 expansion of the leaf, and its walls have the same sinuous out- 

 line that the other epidermal cells exhibit. A curious variation 

 of the ordinary form is seen in Aneimia} where the mother cell 

 of the stoma is cut out by a perfectly circular wall, very much 

 like the funnel-shaped one in the antheridium, and the stoma is 

 apparently free in the centre of an epidermal cell. It seems 

 that this also occurs in Polypodium lingua?- 



1 De Bary (3), p. 42. '-^ De Baiy, I.e. 



