366 



PART IV. CLASSIFICATION. 



Fm. 218. Embryogeny of the sporophyte of Pteris serrulata ( x 235 : after Kienitz-Gerloff). 

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

 embryo in longitudinaj Section. The vertical arrows indicate the long axis of the arche- 

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

 the prothallium, pointing to its organic apex. I-l Bsisal wall; 11-11 transverse wall; 

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

 /foot. 



with the bundle of a'n older leaf, seven leaves intervening between 

 the two. 



Embryogeny of the Sporophi/te. The sporophyte is developed 

 from the fertilised female cell, the oospore : the development has 

 only been studied in species of Polypodiacese, 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 

 icall, 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 at right angles to both the 

 preceding walls, the embryo now consist- 

 ing of eight equal cells or octants. Of 

 these octants, four belong to one half of 

 the embryo, which is termed the cpibasal 

 half; and four to the other half, the 

 hypobasal half: from these octants the 

 primary organs of the sporophyte are 

 developed. Beginning with the four 

 epibasal octants, the two apical octants 

 (i.e. nearest to the neck of the arche- 



FIG. 219,-^Adiantum CapiHus- 

 Venerit. The prothallium (pj>) 

 seen from below with young 

 Fern attached to it by its foot ; i 

 its first leaf or cotyledon ; w' its 

 primary, to" secondary, roots; 

 h root-hairs of the prothallium 

 (x about 3). (After Sachs). 



