1 08 THE SPORANGIUM DEFINED 



he approves of the method by which it is arrived at : that is, the method 

 of recognition of the archesporium by " a last analysis " of cell-origin. 



Secondly, Goebel's method of recognition of the archesporium is not 

 consistent : he designates the inner product of the hypodermal layer in 

 the Angiospermic stamen the archesporium, notwithstanding that the 

 " schichtzellen " and the tapetum are sister-cells with it. But in the 

 Pteridophyta, on the ground of common origin by segmentation, not only 

 the tapetum but also the sporangial wall itself are described as derived 

 from a superficial archesporium. If the recognition of an archesporium 

 is to be based upon "a last analysis" of the segmentations, then the 

 hypodermal layer of the Angiospermic anther, and not merely the inner 

 product of its segmentation, is the archesporium. 



Thirdly, the recognition of the archesporium by the method of "a 

 last analysis" brings together under a common head, merely on the ground 

 of early segmentations, things which are not really comparable, and ascribes 

 a distinct origin to things which are indistinguishable when mature. The 

 superficial archesporium of the Pteridophytes gives rise to part of the 

 sporangial wall and of the tapetum : the archesporium of the Angiospermic 

 anther, on Goebel's definition, gives rise to neither. It is impossible to 

 conceive how by any known evolutionary progression the former type of 

 " archesporium " could pass into the other, and the superficial cells be covered 

 over : therefore the two are to be regarded as not truly comparable. Further, 

 the recognition of superficial cells in the Pteridophytes as archesporial 

 draws a distinction between part of the sporangial wall which originates 

 from them, and the rest which does not : thus in the Leptosporangiate 

 Ferns the apical part of the annulus would be archesporial, the lateral 

 parts would not. 



With all respect to the opinion of the writer who introduced the term, 

 I think that this last change in its application, as suggested by Wilson 

 Smith and accepted by Goebel, makes more obscure the meaning of a 

 word which never has been clear. The Bryophyta provide a reductio ad 

 absurdiun of the method of " a last analysis " ; for, following this method, 

 in Sphagnum and some others the amphithecium would be reckoned as 

 the archesporium, while in the ordinary Bryineae it would be the 

 endothecium : or, carrying the analysis in the latter case to its extreme 

 limit, the- first segments in the upper half of the zygote, or even the 

 ovum itself, would be the archesporium. 



The fact is that this sort of analysis of formative tissues has served 

 its turn : it has led to much detailed investigation, which has, however, 

 shown that the segmentations which lead up to the formation of spore- 

 mother-cells are not comparable in all cases. The time has come, in 

 presence of many divergent details, to admit frankly that there is no 

 general law of segmentation underlying the existence of that cell or cells 

 which " a last analysis " may mark out as the " archesporium," and that 

 therefore the general application of such a term to those cells which the 



