90 STERILISATION 
spore-production before the tetrad-division. It is a secondary matter 
morphologically that in this case their existence is brief; but physiologically 
it is important, for they are sacrificed to furnish better nutrition to the 
‘others which remain fertile, and produce spores. The structure seen in 
Fig. 45 is thus to be interpreted as indicating the sterz/isation of certain of 
the potentially fertile cells in the sporogenous group of Pszlotum. 
A second example illustrating this partial sterilisation of a sporogenous 
group may be quoted: it is selected from among the Bryophytes; but 
the same arguments as in the previous case will equally apply here. 
Fig. 46 illustrates two stages in the development of the sporogonium of 
Aneura: the younger shows the clearly defined, hemispherical internal group 
Fic. 46. 
A, median section of young sporogonium of Aneura amhrosioides. The internal mass 
of cells of the sporogonial ypead (‘‘archesporium”) is already differentiated so as to 
indicate the sterile elaterophore, and the outer fertile region. ZB, the same, older: the 
indications of sterilisation have extended outwards, and it is only the peripheral fringe of 
cells (shaded) which will be sporogenous. C, transverse section of the same. X 150. 
of cells of the sporogonial head, which are equivalent zzer se, inasmuch 
as they have a common origin ; but they are already differentiated into two 
distinct regions, a peripheral fertile region, of which the cells are shaded, 
and a central sterile region. The former differentiates at a later stage into 
spore-mother-cells and elaters: the latter forms the sterile elaterophore. 
The whole hemispherical group corresponds in position to the body 
similarly placed in other Hepaticae, which have no elaterophore, and 
in which the whole region develops into spores and elaters. This case 
therefore illustrates an advanced stage of sterilisation of tissue which may 
be held to be ancestrally sporogenous throughout. But the final fate of 
the sterile cells here is not merely to serve as evanescent nutritive cells ; 
for the elaterophore and elaters are a permanent tissue and permanent 
cells, which remain till the ripeness of the spores, and are functional in 
their dispersal. 
