470 General Botany 



upper side are two divergent grooves in which antheridia and 

 archegonia (singular, archegonium ^) are formed. The antheridia 

 produce the sperms. The archegonium is a flask-shaped organ 

 which contains the egg. Fertilization is effected by the small 

 sperm swimming to the archegonium when the thallus is wet, 

 passing down the neck of the archegonium and fusing with the 

 egg. The oospore, or fertilized egg, germinates directly, pro- 

 ducing a rounded body of cells. The inner cells of this body 

 divide, each forming four spores, while the outer layer of cells 

 forms the sporangium wall. At maturity the sporangium wall 

 breaks, liberating the spores. 



As will become more evident when we study the ferns, this life 

 history is made up of two distinct phases, or generations. The 

 one producing the gametes is called the gametophyte; the one 

 ending with the production of spores is the sporophyte. The 

 gametophyte of all liverworts and mosses is a food-manufacturing 

 phase, the sporophyte is a parasitic phase. 



Other liverworts. Marchantia is a common thallose liverwort 

 found on moist rocks and in swamps. It differs from Riccio- 

 carpus mainly in having specialized branches (Fig. 287), arising 

 from the thallus, on which the antheridia and archegonia are pro- 

 duced. The sporophyte also has a short stalk below the sporan- 

 gium, the base (foot) of which grows downward into the tissue of 

 the gametophyte, thus becoming a distinct absorbing organ. 



Anthoceros is another thallose form, in which the sporophyte 

 is greatly elongated, growing upward from the thallus in which 

 the archegonium is embedded. The anthoceros sporophyte is 

 of further interest because the sporangium wall is several cell 

 layers in thickness and the cells contain chlorophyll. Moreover, 

 the epidermis has guard cells and stomata. 



There are many genera of leafy liverworts, and about 3000 

 species have been described. These forms are very abundant in 



^ The archegonium is found in the mosses, liverworts, ferns, and in gym- 

 nosperms. It is analogous to the oogonium of the algae. 



