Life-history of Tetradinis articulata. 589 
archegonium initials, lag very slightly behind the others. The result of 
this is that the central apical alveoli, instead of growing in simultaneously 
with those immediately surrounding them, grow down on to their walls. 
In this way the apical archegonium initials are from the first distinct from 
all the other alveoli (Figs. 39 and 63). Lands ( 24 ) figure of archegonium 
initials in Thuja rather suggests that a similar lagging of the alveoli which 
will form archegonium initials may take place in that genus (and, doubtless, 
in other Cupresso'fdeae). In contrast with the Callitroideae, the alveoli 
remain unsegmented until they almost meet in the central axis of the pro- 
thallus, and then (except the archegonium initials) divide up more or less 
evenly into several cells ; in the Callitroideae a small tabular cell is cut off 
from the base of each primary cell before it extends more than about half- 
way inwards. In Libocedrus , Lawson ( 27 ) describes the alveoli as forming 
several transverse divisions while they grow inwards, but this does not 
occur in Tetraclinis ; it is likely that there may be differences in this 
respect between closely related plants, as shown by Arnold i (1 and 2 ) in 
the two species of Sequoia. 
The first division of the archegonium initials occurs soon after the 
beginning of segmentation of the primary prothallus cells, and results in 
the formation of the central cell of the archegonium and a primary neck- 
cell (Fig. 40). The neck-cell soon divides again in a vertical plane, and 
each daughter-cell again in the other vertical plane, forming a single tier of 
four cells in the neck. At the same time the central cell rapidly enlarges, 
while the surrounding prothallus cells go on growing and dividing to keep 
pace with it. The archegonia (Figs. 41, 43, and 63-5) form an apical com- 
plex exactly similar to that met with in other Cupressoldeae ; 1 the cells 
immediately surrounding the complex form a fairly well-defined jacket 
layer, as in Thuja , Juniperus , and other genera. The nucleus of the central 
cell at first lies in a small mass of cytoplasm just below the neck. The 
cytoplasm also extends as a thin parietal layer round the inside of the wall, 
but the whole of the central part of the archegonium is occupied by one 
large vacuole (Fig. 63). As the archegonium matures, a small mass of 
protoplasm is also seen at the base of the archegonium, and this gradually 
enlarges so that the vacuole is completely obliterated before the archegonium 
is ready for fertilization (Figs. 41, 64). 
The number of neck-cells also increases during the development of the 
archegonium, there being finally two tiers of neck-cells, sometimes with 
more than four cells in a tier. The arrangement varies somewhat, but the 
commonest type of neck appears to consist of two tiers of four cells each. 
(See Figs. 41, 42, 45, and 46.) 
1 Cunninghamia (Miyake (32)) has a somewhat different arrangement of the archegonia, with 
a patch of sterile cells in the centre of the complex. 
