TAXONOMY 
231 
DIVISION II. — BRYOPHYTA 
Plants showing a beginning of definite alternation of genera- 
tions, i.e., gametophyte (sexual phase) alternating with sporophyte 
(asexual phase of development) in their life history, the two phases 
being combined in one plant. The female sexual cell is always 
lodged in an archegonium (a multicellular female sexual organ). 
Fig. 107. 
Fig. 108. 
Fig. 107. — Section of thallus of Cetraria islandica through an apothecium. as, 
Asci, three of which contain ascospores. gon, Gonidia. The inner (central por- 
tion shows the mycelial threads of a fungus entangling the alga. (Sayre.) 
Fig. 108. — A liverwort (Lunularia) . Below, portions of the thallus, showing 
the lunar-shaped cupules, with brood-buds, or gemmae. Above a single gemma, 
greatly magnified. (Gager.) 
SUBDIVISION I. — HEPATIC/E OR LIVERWORTS 
Plants of aquatic or terrestrial habit whose bodies consist of a 
rather flat, furchate branching thallus or leafy branch which is 
dorsoventral (having distinct upper and lower surface); the upper sur- 
face consists of several layers of cells containing chlorophyll, which 
gives the green color to the plants; the lower surface gives origin to 
hair-like outgrowths of the epidermal cells serving as absorptive parts 
and called rhizoids. Upon the dorsal surface of this thalloid body 
