HEPATIC^. 



347 



ITU 



by the rapid growth of the surrounding tissue of the thallus 

 (A, B, and C, 

 Fig. 232). In 

 other cases the 

 antheridia are de- 

 veloped in great 

 numbers u p o n 

 special branches, 

 as in Marchantia, 

 which has a large 

 *' antheridial disc" 

 (A and B, Fig. 

 231, hu), in whose 

 upper surface are 

 to be found many 

 imbedded anther- 

 idia. That the an- 

 theridia are actu- 

 ally external in 

 this case also, be- 

 coming apparent- 

 ly internal by the 

 growing up of the 

 .surrounding tis- 

 sues, is well shown 

 in Fig. 233. In 

 still other cases 

 (e.g., in Junger- 

 tnanniacece) the 

 antheridia are in 

 the axils of the 

 leaves, and occur 

 singly or in groups. 

 453. The ar- 

 chegonium first 

 appears as a simple 

 papilla, composed 

 of a single cell, 

 which, by subdi- 

 vision in va" 'ous 



Fig. 235. The archegonia, and origin of the sporogo- 

 nium otMarehantia polymorpha. I. and //., young arche- 

 gonia ; e, germ cell ; si, lowest cell of axial row of cells. 

 111. and IV., the same after the formation of a central 

 canal by the absorption of the axial row of cells in the 

 neck. V., the same when mature and ready for fertiliza- 

 tion. VI., the ba<e of a fertilized archeaonium. the 

 germ-cell,/, divided into two cells by a diagonal partition. 

 VlL, later stage of the same, showing further division of 

 the germ-cell, /. and the beginning of the growth of a 

 perianth, pp. VIII., still later stage of the same, the 

 perianth, pp, now enclosing the archegonium ; x, the 

 withered neck of the archegonium. IX., the unripe up_oro- 

 gonium, enclosed in the old walls of the archegonium, 

 now called the calyptra, a ; /, wall of gporogonium ; 

 ft, the short, undeveloped stalk of the eporogoninm. 

 Inside of the sporosronium are the young elaters arranged 

 radially, and between them are the spores. /. to VIII. 

 X 300 ; IX. about 30. Alter Sachs. 



directions, gives rise to a more or less 



