296 
F. Cavers. 
plant-body of Metzgeriopsis, which may be regarded as a persistent 
protonema, agrees exactly with the thallus of a Metzgeria. The 
early stages in germination of the spore are precisely alike in 
Metzgeria and the Lejeuneas; in both cases, after one or two trans¬ 
verse divisions have taken place in the short germ-tube, the distal 
cell gives rise to a two-sided apical cell and a ribbon-like protonema 
is formed. In Metzgeria and in Metzgeriopsis the protonema con¬ 
tinues to grow as a flat thallus; in Metzgeria a midrib is formed 
and the protonema develops directly into the adult thallus, while in 
Metzgeriopsis the persistent protonema or thallus gives rise eventually 
to the leafy sexual shoots. Moreover, Metzgeria and the Lejeuneae 
agree in producing discoid gemmae, but in this respect the two 
genera simply illustrate what appears to be a general rule in the 
Hepaticae, namely, that the protonema and the gemmae of any given 
species usually show a close resemblance in form. 
As an indication that too much stress should not be laid upon 
the mode of germination and the form of the protonema in the 
different groups of Hepatioae, it may he pointed out that there are 
great variations in this respect amongst allied forms. The germi¬ 
nation of a considerable number of Hepaticae has been described 
by Gronland (37), Leitgeb (56), Campbell (3), Frau Lampa (51). 
Douin (9), Goebel (32), and others. In Hepaticae, as in Mosses, 
the development of the gametophyte is “ heteroblastic,” since there 
is first formed a protonema or “ pro-embryo ” of simple form, and 
from this the adult plant arises, usually from a terminal cell which 
becomes the apical cell of the plant-body. As a rule, the spore 
contents grow out to form a positively heliotropic and usually 
unbranched filament or germ-tube in the first instance, and the 
apical cell of the adult plant may either arise from the terminal 
cell of this filament (most Acrogynae), or the formation of a germ- 
tube may be more or less completely suppressed so that the 
protonema forms a cell-surface or disc; the young plant arising 
from one of the marginal cells. A germ-disc is formed directly 
from the spore in Radula, for instance ; in Frullania and Porella, 
divisions occur in all directions of space, producing a solid ovoid 
protonema instead of a discoid cell-surface. In various other 
genera of Acrogynae, we find transitions from the germ-tube to the 
germ-disc types of protonema; sometimes both types are found in 
the same species. 
In the other groups of Hepaticae, we find similar diversity in 
the form of protonema. Among the Anacrogynae, Anenra 
