398 



PART III. THE CLASSIFICATION OF PLANTS. 



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 epibasal 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 archegonium) give rise to the growing-point of the first 

 leaf or cotyledon: of the two deeper (towards the venter of arche- 

 gonium) octants, the one constitutes the growing-point of the 

 stem, whilst the other gives rise to nothing beyond possibly some 



hairs. Of 

 the four hy- 

 pobasal oc- 

 tants, one of 

 the two api- 

 cal octants 

 gives rise to 

 the growing- 

 point of the 

 primary root, 

 which is dia- 

 metrically 

 opposite to 

 the growing 

 point of the 

 stem ; whilst 

 the other 

 gives rise to 

 no special 

 member : the 

 two deeper 

 hypobasal 



octants give rise to the embryonic absorptive organ, the foot. 

 The gradual development of these members is dependent upon 

 growth and corresponding cell- division, and at an early stage 

 histological differentiation into cortical and stelar tissues is 

 apparent in them. For a time the tissue of the venter of the 

 archegonium keeps pace by growth with the increasing size of the 

 embryo : but eventually the primary root and the cotyledon become 

 free, and ultimately also the stem (Fig. 264). In the meantime the 

 embryo is nourished by means of the foot which has become a mass 



FJG. 264. Section of young plant of Pteris aquilina still attached 

 to the prothallium by;its foot: p prothallium ; /foot; r primary root ; 

 s growing-point of primary stem ; I primary leaf or cotyledon. (Mag- 

 nified: after Hofmeister.) 



