BRYOPHYTES 



97 



liverworts, being only a spore case, and from such a structure many sup- 

 pose that sporophytes of the higher plants have developed. This primi- 

 tive sporophyte is dependent in a large measure upon the gameto- 

 phyte for its nutrition, so that it appears simply as a spore case 

 developed by the gametophyte. 



The gametophyte, on the other hand, is far from being the simplest 

 gametophyte known among liverworts, being quite complex in structure. 

 The simplest liverworts should combine the simplest gametophyte with 



Figs. 221-226. — Riccia: development of the sporophyte (sporogonium) ; 221, first 

 division of the fertilized egg (oospore), transverse to the long axis of ihe archegonium; 

 222, quadrant or octant stage; 223, still later stage; 224, the coming in of pericjinal 

 walls that separate the amphithecium (outer layer of cells) from the endothecium (after 

 Garber); 225, portion of sporophyte showing three of the numerous free mother cells 

 produced, and the investing calyptra (two layers of cells) ; 226, tetrads (of spores) pro- 

 duced by the mother cells. 



the simplest sporophyte, but such a combination is not known, and per- 

 haps it no longer exists. It follows that while the history of the liver- 

 wort sporophyte may well begin with the Ricciaceae, the history of the 

 liverwort gametophyte must begin with other forms. 



Marchantiaceae. ^ — This family includes the most highly specialized 

 of the Marchantiales. The familiar genus Marchantia may be used as 

 an illustration. 



Gametophyte. — The gametophyte body is a highly developed thallus, 

 whose dorsal region contains a series of large air chambers domed by the 

 epidermis and containing special chloroplast-containing cells (fig. 227). 



