312 
PLANT STUDIES 
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. 286. Marchantia polymorpha, a common liverwort : 1, thallus, with rhizoids, 
bearing a mature archegonial branch (/) and several younger ones (a, b, c, d, e); 
3 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. 283, B). 
