I 12 
Lillian O'Keeffe. 
may he divided into two stages separated by the occurrence of 
fertilisation, which appears to be essential for the beginning of the 
second stage. In the first stage the involucre reaches the condition 
just described— i.e., it consists of two crescentic ridges which 
together with the archegonial depression form an ovoid cavity 
having its longer axis in the median line of the thallus and having 
the margins separated by a gap (through which enter the anthero- 
zoids), and it projects very slightly from the general surface of the 
thallus. After fertilisation has taken place, the two valves or 
ridges undergo active growth, the cavity being greatly enlarged ; 
the margins come together and the walls of the cells in this region 
become thickened, cutinised and coloured reddish or violet (the 
same changes taking place over the outer surface of the valves), 
the cells at the margins become tooth-like and form interlocking 
processes which cause the complete closure of the involucre (Fig. 2, 
A, D). The suture thus formed is easily separated by pressure on 
the involucre, which can thus be made to gape widely open (Fig. 2, E), 
so that there is no fusion of the marginal cells, merely an inter- 
digitation of the tooth-like processes. 
V. Sporogonium. 
The early stages in development of the sporogonium were 
followed in some detail, and were found to differ somewhat from 
what has generally been described as the typical embryogeny of 
Marchantiales, namely, the early formation of an octant stage. 
No such stage was observed, all the young embryos seen consisting 
of a single row of as many as five cells, but more often either three 
or four (Fig. 2, B, C), before any longitudinal divisions had taken 
place. This “ filamentous ” type of embryo has generally been 
regarded as typical for the Jungermanniales, as opposed to the 
early octant formation characteristic of Marchantiales, but Meyer 
(11) has recently described a similar cell-row in the early embryogeny 
of Plagiochasma, his figures closely agreeing with the series observed 
by me in Targionia. Since only one sporogonium is formed in each 
involucre, i.e., on each shoot, it is less easy to obtain a complete 
series of stages in Targionia than in the higher Marchantiales where 
each archegoniophore produces a number of sporogonia, but a 
fairly good consecutive series was obtained showing all the chief 
stages from fertilised egg to nearly mature sporogonium. The 
differentiation of the one-layered capsule wall from the central 
fertile tissue takes place at a fairly early, stage, the periclina! 
