THE GEEAT GROUPS OF BEYOPHYTES 



113 



cells more or less modified for conduction. Above these 

 the dorsal region is organized into a series of large air cham- 

 bers, into which project chlorophyll-containing cells in the 



FIG. 97. Marchantia polymorpha, a common liverwort : 1, thallus, with rhizoids, 

 bearing a mature archegonial branch (/) and several younger ones (a, b, c, d, ); 

 8 and 3, dorsal and ventral views of archegonial disk; U and 5, young sporophyte 

 (sporogonium) embryos; 6, more mature sporogonium still within enlarged venter 

 of archegonium; 7, mature sporogonium discharging spores; 8, three spores and 

 an elater. After KNY. 



form of short branching filaments. Overarching the air 

 chambers is the dorsal epidermis,, and piercing through it 

 into each air chamber is a conspicuous air pore (Fig. 94, B). 



