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 i 

 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 



^Annals of Botany, vol. viii., p. 316. 



