CH. XI] 



THE LIVERWORTS 



481 



closing stomata. In these chambers is the chlorenchyma, 

 in loosely-arranged lines of cells, an arrangement unusual 

 in Liverworts, and one of several features in which Mar- 

 chantia is peculiarly specialized. The thalli are dioecious, 



FIG. 340. The life cycle of Marchantia polymorpha. 



Left, thalli with archegonial and antheridial receptacles, and (on lower) 

 gemmae cups ; X |. Upper line, receptacles in median vertical section, 

 showing archegonia and antheridia, and the characteristic air chambers, 

 X 5, and also an archegonium, with sperm cells, and an antheridium, in 

 section, X 20. Lower line, ripening sporogonium, X 45, ripe sporangium 

 emitting spores intermingled with elaters, X 10, a spore and portion of an 

 elater, X 300, and a spore germinating to a thallus, X 120. (Adapted from 

 L. Kny.) 



and the archegonia and antheridia are borne upon um- 

 brella-shaped RECEPTACLES, which are upgrowths of the 

 thallus midrib ; and thus is explained the presence of bundles 

 of rhizoids in unclosed tubes in the stalks of the receptacles. 

 The antheridia, containing great numbers of regularly- 

 arranged sperm mother cells, are borne in pits on the upper 

 surface of the male receptacles, while the archegonia lie on 

 2i 



