92 STERILISATION 
Such examples serve to show that there are good grounds for holding 
that sterilisation of individual cells of the sporophyte, which by their origin 
are to be recognised as potentially fertile, does take place; and that such 
cells may be diverted to a temporary, or to a more permanent use 
in connection with the production of spores. Thus we are justified 
in holding that sterilisation, which is the initial factor in the 
working hypothesis sketched in the previous chapter, has been actually 
operative. , 
It will be impossible here to enumerate all the cases where evidence of 
sterilisation of potentially fertile cells has been brought forward ; but some 
of the more prominent instances of it 
will be quoted. At present it is the 
mere fact of sterilisation which is before 
us, not the biological consequences 
which follow in facilitating the nutrition 
or the dispersal of spores, nor yet the 
morphological advances which may 
result. These aspects of the matter 
will be left over till the several groups 
of the Archegoniatae are specially 
discussed. 
Among the Liverworts the simple 
Ricciaceae have céntrally an undiffer- 
entiated sporogenous tissue; but as a 
rule in the Marchantiaceae and Junger- 
manniaceae the almost spherical mass 
of sporogenous tissue becomes differ- 
entiated as development proceeds: 
cells, singly or in groups, instead of 
undergoing the  tetrad-division, are 
Fic. 48. developed in a vegetative manner, 
__Matlan longitudinal section of « sporogoniun either as nutritive cells (Sphaerocarpus), 
ees ewe P' or as elaters of various form and 
arrangement (compare Fig. 46, of 
Aneura). In the Anthocerotaceae, on the other hand, the archesporium 
is a dome-shaped layer surrounding a central columella; but the products 
of this layer do not only form spore-mother-cells, but also numerous 
sterile cells arise from it, which develop as an irregular network enclosing 
the mature spores. In point of fact, in the Liverworts it is the exception 
rather than the rule for the whole of the sporogenous tissue to be fertile, 
though this is the case in the simplest of them. 
In the Musci, on the other hand, the whole of the cells developed 
from the definite, single-layered archesporium normally produce spores ; 
but the archesporium is relatively small compared with the bulk of the 
young sporogonium: it shows an apparently arbitrary limitation at its 
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