168 
F. Cavers. 
structure (Fig. 19, V.), giving the fruiting carpocephalum a very 
characteristic appearance, since it protrudes beyond the involucre 
and its margin is cut up into from four to sixteen long narrow 
segments, which in some species remain attached at the tips and 
serve to bring about the gradual dispersal of the spores by acting 
as a “ censer mechanism.” Campbell (8) has shown that in F. 
californica the carpocephalum is “ Composite,” as in Cryptomitrium, 
each of the four involucres containing a group of four archegonia 
as a rule. In F. Lindenbergiana, several receptacles were found by 
the writer to contain two, three, or four archegonia in some of the 
involucres, and probably the same will be found in other species of 
this genus. 
III.—Compositae. 
This group contains eight genera— Exormotlieca, Fegatella, 
Lunularia, Wiesnerella, Dumortiera, Bucegia, Preissia, and Mar¬ 
chant ia, all poor in species except Marchantia. 
The air-chambers are arranged in a single layer, except in 
Bucegia, where they are partitioned up as in Reboulia and the other 
typical Operculatae. There are usually assimilating filaments filling 
up the chambers, but exceptions occur (apart from Bucegia) in the 
genus Dumortiera, in which the air-chamber layer shows great 
reduction. The extent of the reduction varies in different species, 
and in the same species according to the conditions of the habitat 
with reference to moisture and shade. In D. hirsuta (in which D. 
irrigua is merged by Stephani) the air-chambers are laid down at 
the growing-point and, as shown by Coker (17), in plants grown 
under fairly dry conditions may persist and be roofed over, but in 
conditions of shade and moisture (in which the plant usually grows) 
the chambers become disorganised and are only recognisable in the 
parts behind the apex by the remains of the vertical partitions. In 
D. velutina, the partition-walls and the roofing layer soon become 
completely disorganised, but the thallus is densely clad with out¬ 
growths corresponding to the assimilating filaments which fill the 
chambers in other genera. In D. trichocepliala, according to 
Campbell (8), there is no trace whatever of the chambers even at 
the growing-point, but Ernst (20) and Kamerling (29) found that 
the assimilating filaments are represented by short projecting 
papillae. In Bucegia, Preissia, and Marchantia, the thallus pores are 
barrel-shaped, but in the other genera (as in the Operculatae) this 
type of pore is confined to the sexual receptacles, the pores on the 
