MOSSES AKD LIVERWORTS (BKYOPHYTES) 267 



upper surface. From these there escape large numbers of cells, 

 each of which produces a sperm. Sperms enter the neck of 

 the archegonium and one unites with the egg, thus producing 

 an oospore. 



The oospore does not grow directly into a new plant, but 

 produces an enlarged spherical body which is embedded in the 

 tissues. After a time all of this spherical body except a single 

 layer of outside cells divides into spores. These escape by the 

 breaking down of the tissues of old plants. They may grow 

 into new Riccia plants. 



The main Riccia body is the gametophyte, since it produces 

 the gametes which form the oospore. The sporophyte which 

 develops from the oospore is very simple. It is entirely em- 

 bedded within the gametophyte body. All of it forms spores 

 except a single outside layer of cells. Alternation of genera- 

 tions is as truly present as in the mosses but is not nearly so 

 conspicuous. 



249. Marchantia: vegetative characteristics. This liverwort 

 grows in moist places, such as swampy regions, shaded river 

 banks, and protected rocky ledges. Sometimes it forms exten- 

 sive mats, completely covering the material upon which it 

 grows. Single plants may become several inches in length 

 and breadth and many layers of cells in thickness. Its well- 

 differentiated upper and lower surfaces, apical and basal 

 regions, and masses of rhizoids, which are sometimes an inch 

 or two in length, are features which were less developed in 

 Riccia. The plants grow forward, the lobes continuing to 

 branch, until at times quite extensive growths are produced 

 (Fig. 223). Older portions may die, leaving the younger 

 branches as new and independent plants. 



The nutritive tissues of Marchantia are highly developed. 

 There are chains of special chlorophyll-bearing cells in the 

 upper tissues. These semi-open spaces or chambers are near 

 the upper surface of the plant. The surface outline of these 

 is diamond-shaped. Each diamond-shaped superficial layer of 

 cells has in its center a chimney-like pore through which there 



