426. PHARMACEUTICAL BOTANY 
surface of soil in flower pots of greenhouses and on the damp 
rocks and humous soil of woodlands. 
GAMETOPHYTE GENERATION.—The gametophyte or sexual 
plant consists of a dichotomously branched thalloid body with a 
distinct midrib. With a hand lens it will be noted that its green 
upper surface exhibits numerous pale green lines which divide it 
into small rhomboidal-shaped areas. In the center of each of 
these is a pore which leads into an air-chamber within the body. 
Its lower surface is nearly colorless and exhibits rhizoids and 
delicate scales. 
Guard Cell _ mina Guard Cell Upper Epidermis 
Air Chambers 
Partition sey rs 2 ce cae ae 
between Air--> a & g 
Chambers 
Lower 
Epidermis” ~ 
Rhizoid 
Fic. 312.—Marchantia polymorpha. Microscopical structure of the thallus which 
shows dorsioventral differentiation. A, vertical section showing one large air- 
cavity beneath the epidermis. B, C, D, portions of each of three kinds of rhizoids, 
the last two with inner thickenings of the wall. (Moittier.) 
A cross section of the thalloid body, when examined micro- 
scopically, will disclose an upper epidermis of epidermal cells 
containing chloroplasts and showing stomata, each stoma sur- 
rounded by four vertical rows of cells. Directly beneath this is a 
row of air-chambers separated by partitions. In each air-cham- 
ber branched rows of densely chlorophylloid cells grow upward from 
the cells which constitute its floor. ‘These do most of the work 
of photosynthesis. Below the air-chambers are several rows of 
clear parenchyma cells containing only a few chloroplasts. 
From the lower surface of these are to be noted outgrowths as 
slender rhizoids and scales. 
Some of the gametophytes will show cup-like structures on 
their upper surface. These are called cupules. They contain 
