GROUP III. PTERIDOPHYTA : FILICIN^ ; LEPTOSPORANGIATJE. 397 



present towards the surface where the leaves are borne ; i.e. 

 towards the dorsal surface (see p. 388). 



In a monostelic stem, such as that of Osmunda, though the 



FIG. 262. Embryogeny of the sporopbyte of Pteris serrulata ( x 2S5 : after Kienitz-Gerloff ). 

 A In longitudinal section : B transverse section, at right angles to the preceding : C older 

 embryo in longitudinal section. The vertical arrows indicate the long axis of the arche- 

 gonium, pointing to the neck : the horizontal arrows indicate the longitudinal axis of 

 the prothallium, pointing to its organic apex. I-I Basal wall; II-II transverse wall; 

 Ill-Ill median wall : r apical cell of root ; I apical cell of cotyledon ; s apical cell of stem ; 

 / foot. 



bundles are numerous, no such meshwork is formed. The bundles 

 are here common. A single bundle enters the stem from each 

 leaf, runs straight through several in- 

 ternodes, and then curves to join with 

 the bundle of an older leaf, seven leaves 

 intervening between the two. 



Embryogeny of the Sporophyte. The 

 sporophyte is developed from the fertil- 

 ised female cell, the oospore : the de- 

 velopment has only been studied in 

 species of Polypodiaceae, and has been 

 found to be as follows. The oospore is 

 first of all divided into two cells by the 

 formation of a wall, the basal wall, which 

 nearly coincides with the long axis of 

 the archegonium : a second wall is then 

 formed, the transverse wall, at right 

 angles to the preceding, with the result 

 that the spherical embryo now consists 

 of four cells or quadrants : then a third 

 wall, the median wall, is formed in a plane 



FIG. 263. Adiantum Capillus- 

 Veneris. The prothallium (pp) 

 seen from below with young 

 Fern attached to it by its foot ; b 

 its first leaf or cotyledon ; w' its 

 primary, to" secondary, roots; 

 7i root-hairs of the prothallium 

 (x about 3). (After Sachs). 



