HEPA TIC/E. 
353 
segmental cells, near to the growing-point of the thallus, divides into an outer and 
an inner cell ; the outer (superior), which bulges slightly, is the mother-cell of the 
archegonium and is further divided (as is the case in other Liverworts) by three longi- 
tudinal walls vertical to the surface of the thallus, into one internal and three external 
cells. The latter produce the six primary investing cells which, at a later period, 
give rise to as many rows of cells which are enclosed on all sides by the tissue of 
the thallus. The internal cell is divided by a transverse septum into two cells, the 
lower of which becomes the central-cell, and by division gives rise to the oosphere and 
the overlying ventral canal-cell ; the upper undergoes transverse divisions in consequence 
of which a row of neck canal-cells is formed, as also the primary stigraatic cell which 
subsequently divides cross-wise to form the stigmatic cells. The variations from the 
mode of formation of the archegonium obtaining in the other Liverworts are thus seen 
to be slight, and scarcely justify the formation of the Anthocerotese into a distinct class. 
Fig. 237 C dates from a time at which the above-mentioned details were unknown, but 
it suffices nevertheless to give some idea of the important points in the process. 
After fertilisation the oospore is divided in the manner described above. Whilst 
the developing sporogonium is gradually becoming a multicellular body dilated inferiorly 
Fig. ■2-yi.—Anthoceros lavis (after Hofmeistei") ; A a branclied thallus; B longitudinal section of a shoot (X 40); cin 
antheridia beneath the layer of superficial cells ; C longitudinal section through the apical part of a slioot ; nr rudiments of 
archeg-onia (X 500) ; D nr fertilised archeg-onium in the longitudinal section of a shoot, with an embryo consisting of 
two cells ; E multicellular embryo : Ä' in ä a colony of Nostoc settled in the tissue of the thallus. 
(Fig. 237, E)^ the cells of the surrounding tissue of the thallus undergo numerous 
divisions and form an upwardly projecting involucre which is broken through at a later 
period by the elongating sporogonium. Differentiation now takes place in the homo- 
geneous tissue of the sporogonium ; a central cylinder of from twelve to sixteen rows 
of axially elongated cells is marked out, forming the columella, whilst the cells of the 
layer immediately adjacent to it undergo division by horizontal walls and give rise to the 
mother-cells of the spores and elaters ; the external four or five layers of cells form the 
wall of the future ' pod.' Those cells of the layer investing the columella which are to 
form elaters undergo one or more vertical divisions. The elaters are here transversely 
directed rows of cells in which no spiral bands are formed. The mother-cells of the 
spores round themselves off, become gradually isolated, beginning from the apex of the 
sporogonium and proceeding basipetally, increase in size, and then divide into four, giving 
rise to the tetrahedral spores. The sporogonium elongates and becomes a pod-shaped 
structure of from fifteen to twenty millimetres in height, the brown wall of which, 
provided with an epidermis bearing stomata, splits from above downwards into two 
valves. 
A a 
