173 
Phytogeny of Marchant tales. 
by the downward growth of the tissue of the branch and somewhat 
resembling the bilobed involucre of Targionia. In most species of 
Marcliantia, however, there are, alternating with the involucres, 
hollow lobes from which spring the rhizoids that pass into the 
furrows of the stalk. In M. polymorpha these lobes grow out to 
form long hollow rays, of which there are generally nine—one in 
excess of the number of involucres. The same numerical relation 
is seen in other species of Marcliantia with alternating involucres 
and lobes; the number of involucres varies from four to ten, and 
there is always one involucre short as compared with the number of 
lobes. However, the morphology of the carpocephalum will be 
discussed presently in considering thephylogeny of the Marchantiales. 
The capsule-wall has ring-fibres, except in Lunularia where 
their complete absence recalls the capsule structure of the 
Operculatee. In Fegatella, Lunularia, and Duinortiera there is a 
well-developed apical thickening which is thrown off as a lid, the 
lower portion of the capsule then splitting into from four to eight 
teeth. In the other genera the apical cap is only indicated by an 
imperfect or loose layer of cells lying within the normally single¬ 
layered capsule-wall at the apex, and the capsule opens by teeth 
extending to the apex. 
» 
Phylogeny of the Marchantiales. 
From our survey of the Marchantiales, it is evident that on the 
whole we can trace within this phylum, starting from Riccia, a 
general advance in the elaboration of the vegetative organs, the 
aggregation of the sexual organs into gametophores of increasingly 
complex organisation, and a progressive differentiation of the 
sporogonium. 
The simplest thallus structure is that seen in most species of 
Riccia, where the upper tissue consists of filaments separated by 
narrow air-spaces. But within the genus Riccia itself we find the 
higher type of assimilating tissue which is characteristic of the 
Marchantiales as a whole—the widening of the spaces to form 
roofed-over chambers, with or without the partitioning up of the 
chambers so as to form a spongy mass of tissue. In the higher 
Marchantiales, practically the only further advances made in the 
elaboration of the air-chamber zone are the development of assimi¬ 
lating filaments by outgrowth of the cells forming the floor of the 
uniseriate chambers ( Corsinia, Boschia, Targionia, some species of 
Grimaldia and Fimbriaria, all the Composite except Bucegia); and 
