THE ARCHESPORIUM 109 
analysis discloses has no scientific meaning, beyond the statement of the 
histiogenic fact. At the same time, the value of the details which have 
been acquired by the pursuit of the archesporium must not be under- 
estimated for purposes of comparison. What is dangerous is the attachment 
to them of ulterior ideas: the assumption that because a definite 
“‘archesporium” is often found, it should by rights be always present: 
and the effort to trace in its appearance homologies which seem based 
‘on forced rather than on natural comparisons. On the other hand, the 
term has become so established in the literature of the subject that it cannot 
be summarily discarded: it may be retained merely in a descriptive sense, 
in those cases where the cell or cells which give rise to the sporogenous 
group are obvious, but in a descriptive sense only. 
The discrepancies which become apparent in the course of develop- 
ment between different types of sporangia tend. to justify the position 
already adopted by Strasburger on general grounds: he remarks} 
that the centre of gravity of the developmental processes does 
not lie in those cells, cell-rows, or cell-aggregates which have been 
designated ‘“archesporium” by Goebel: the archesporium still belongs to 
the asexual generation, and the presence or absence of a well-defined 
archesporium is not a matter of importance, for it is merely the merismatic 
tissue from which the spore-mother-cells are derived. From the point of 
view of a theory of sterilisation as enunciated above, these spore-mother-cells 
may be held to be, in the simpler cases at least, the residuum which a 
progressive vegetative change has left: in that case there is no reason to 
expect that the demarcation of these islands of fertile tissue should have 
followed any definite system in plants at large, which would be reflected with 
any exact uniformity in the segmentations now involved in their formation. 
The frequency of hypodermal origin of the sporogenous tissue in 
Vascular Plants is readily intelligible biologically. In all except the very 
‘simplest sporophytes the spores are protected during development by tissues 
which surround them completely: this ensures nutrition and mechanical 
protection. In the Bryophyta the scattering of the spores would be equally 
efficient whether they be produced close to the surface or deeply seated, 
since the dehiscence, whether by a terminal operculum or by longitudinal 
Slits, gives free exit to all the spores of the continuous spore-sac, and 
accordingly the spore-mother-cells of the Bryophytes may be central, as 
in many Hepatics, or removed more or less from the centre by the 
‘occurrence of a columella, as in most Mosses. But in all Vascular Plants, 
where the spores are produced in separate pockets or sporangia, the 
dehiscence leading to dissemination ‘is referred to the several sporangia 
themselves: this necessitates for them a superficial position on the plant- 
body, or, better, that they shall project beyond the surface. The hypo- 
dermal origin of the sporogenous tissue which is so frequent, may thus be 
recognised as a compromise between the two requirements of effective 
1 Annals of Botany, vol. viii., p. 316. 
