io8 
F. Cavers. 
cells of the thallus, the presence of a row of initial cells at the 
growing-point, and the formation of an octant-stage in the embryo- 
geny—all of which are characteristic of the Marchantiales as 
distinguished from the Jungermanniales ; the male receptacle was 
shown to differ from that of Fegatella (which it superficially 
resembles) by having a single anterior growing-point, as in the 
lower Marchantiales. A little later appeared a detailed paper by 
Johnson (12) on material collected in Jamaica, in which it was 
shown that the narrow rhizoids have the tubercles characteristic of 
the corresponding rhizoids of Marchantiales. 
The thallus (Fig. 14) has a perfectly smooth upper surface, and 
there are no traces of air-chambers ; while the only appendages on 
the lower side, in addition to the rhizoids, are the long club-shaped 
hairs which bend up over the growing-point (Fig. 15). The absence 
of chambers and of ventral scales, and the feeble development of 
tubercles in the narrow rhizoids, may be correlated with the 
extremely hygrophilous habitat of the plant. Coker (6) has shown 
that plants of Duniortiera hirsuta (allied to Marchantia) growing on 
porous sandy soil had well-developed air-chambers, while other 
plants that were constantly wet with dripping water had no trace of 
chambers. In Dumortiera irrigua, chambers are formed at the 
apex of the thallus, but soon become disorganised and are repre¬ 
sented in the older parts only by the remains of the vertical walls, 
which form a network. Campbell (1) found that in D. trichocephala 
no trace of chambers can be detected even at the apex of the 
thallus. Hence in this hygrophilous genus we find every stage in 
the reduction of the chambers, related to the conditions of the 
habitat. Even in Marchantia itself, submerged plants or branches 
show a similar reduction of the chambers ; and in Fegatella the 
writer (5) found that the submerged form had greatly reduced 
ventral scales and hardly a trace of tubercles in the rhizoids borne 
in the axils of the scales. 
The only objections that can be urged against placing Monoclea 
in the Marchantiales are found in the position of the archegonia 
and in the form of the mature sporogonium. The archegonia are 
developed in a pit (Fig. 16) which becomes drawn out to form a 
long tube, much as in Pellia. However, the development of the 
tubular involucre of Monoclea is not in reality widely different from 
that of the hood-like involucre of the Corsiniaceae or the two-lobed 
involucre of the Targioniaceae. In these plants, as in Monolcea, the 
archegonia are produced on an unspecialised portion of the thallus, 
