CHAPTEK XX 
THE GREAT GROUPS OF BRYOPHYTES 
HEPATIC^E (Liverworts) 
202. General character. Liverworts live in a variety of 
conditions, some floating on the water, many in damp 
places, and many on the bark of trees. In general they are 
moisture-loving plants (hydrophytes), though some can en- 
dure great dryness. The gametophyte body is prostrate, 
though there may be erect and leafless gametophores. 
This prostrate habit develops a dorsiventral body that 
is, one whose two surfaces (dorsal and ventral) are exposed 
to different conditions and become unlike in structure. In 
Liverworts the ventral surface is against the substratum, 
and puts out numerous hair-like processes (rhizoids) for ab- 
sorption and anchorage. The dorsal region is exposed to 
the light and its cells develop chlorophyll. If the thallus 
is thin, chlorophyll is developed in all the cells ; if it be so 
thick that the light is cut off from the ventral cells, the 
thallus is differentiated into a green dorsal region doing the 
chlorophyll work, and a colorless ventral region producing 
absorbing rhizoids. This latter represents a simple differ- 
entiation of the nutritive body into working regions, the 
ventral region absorbing material and conducting it to the 
green dorsal cells which use it in making food. 
There seems to have been at least three main lines of 
development among Liverworts, each beginning in forms 
with a very simple thallus, and developing in different di- 
rections. They are briefly indicated as follows : 
