12 HEPATICAE 
Class НЕРАТІСАЕ. 
Protonema very small, often rudimentary. Gametophore thal- | 
lose or foliose or, in a few genera, of a character intermediate 
between these two types, mostly dorsiventral. Leaves, when | 
present, composed of a single layer of cells, never with a true | 
midvein, arranged upon the stem in two lateral ranks,* with some- 
times a more or less well-developed ventral (third) rank. Root- | 
hairs unicellular. Chloroplasts small, several or many in a cell | 
in the assimilative parts. — Antheridia and archegonia arising each | 
from the subdivisions of a surface cell; archegonium individual- 
ized, its wall (except, rarely, the basal portion of the venter) al- | 
ways free from the adjacent tissues. 2 
Sporogonium permanently enclosed within the modified arche- 3 
gonium wall (calyptra) or more frequently included until the q 
capsule is nearly mature, when the calyptra is ruptured near the | 
top by the growth of the capsule ог by the elongation of the seta. - 
Capsule without columella and without stomata, irregularly dehis- - 
cent, operculate, ог more often opening by (usually) four valves. | 
Spores ripening simultaneously, accompanied (except in Ricciaceae) | 
by elongated, thin-walled sterile cells which (with rare exceptions) 
are provided with spiral thickenings (when each sterile cell is 
known as an elater). 
чат 
ааа 
| Order I. MARCHANTIALES. + | 
Gametophore a thallus, consisting of several distinct layers of | 
tissue, the usually clearly defined dorsal epidermis | containing 
pores (‘‘stomata” $) which communicate with narrow vertical 
* Except in a very few genera, none of which are known to occur in California. 
T For diagnosis of Order II а ыгар, see page 62. | 
і Dumortiera, not yet found in California, has а very ы thallus, being. 
without perceptibly кете epidermis, pores, ог air-chamber: 
| so-called “ stomata” of the gametophore of the маны: are quite dif- 
ferent in structure from the stomata of the sporophyte in the Ат лћосетоге;, Миза, 
неар апа 2-57 and are, perhaps, only in part analogous in function. 
But “оша” as applied to the <“ breathing pore," together with its more or less modi- 
fied pe ermal ин is a convenient term in the description of the Marchan- 
tiales and the use of the word in.this extended sense is з sanctioned by Lindberg, Schiff- 
ner, плин. and others. 
