io6 THE SPORANGIUM DEFINED 



It remains to consider the archesporium, and the sporogenous group 

 and spores which arise from it. An archesporium, in one form or another, 

 is a necessary constant in the development of a fertile sporangium : the 

 form, the limits, the mode of origin and of later segmentation which it 

 shows, may vary, as indeed is seen to be the case in the different sporangial 

 types ; but whatever its variations may be, it is in the archesporium, and 

 in the sporogenous cells which it produces, that we see the essential feature 

 of the sporangium. It will be necessary, then, to examine it carefully, 

 and to see how far it is possible to attach a definite meaning to it. 



The term archesporium was introduced by Goebel, 1 and defined as 

 follows : " In the Vascular Cryptogams, as in the Phanerogams, the 

 spore-producing tissue may be universally referred as regards its origin 

 to a cell, a cell-row, or a cell-sheet : I designate these original parent 

 cells of the sporogenous tissue as the archesporium." To this he added 

 that "in all Vascular Cryptogams examined an hypodermal archesporium 

 exists," thus definitely localising it in a position comparable to that 

 in the Spermophyta. He remarks, however, later that he does not lay 

 special stress upon the archesporium being always a cell-row or cell-sheet, 

 and contemplates it as possible that sometimes the development may 

 proceed otherwise than by the appearance of an archesporium of the 

 form described. An examination of all the types of sporangia of living 

 Pteridophytes has shown that this is the fact : a considerable number of 

 cases have been observed in which the archesporium is not hypodermal, 

 in that it is not defined by a single periclinal wall of the parent cells 

 involved. The existence of many exceptions among Eusporangiate 

 Pteridophytes suggests a reconsideration of the archesporium. We may 

 enquire whether a definite meaning is attached to the term, and if so, 

 whether that meaning is of general application. 



The effect of Goebel's investigations on the sporangia of Pteridophytes 

 was to extend downwards from the Phanerogams the demonstration of a 

 formative cell or cells to which the origin of the spores may be ascribed. 

 Before iSSo it was held that a mass of cells within the young sporangium, 

 showing irregular divisions, took upon them the character of a sporogenous 

 tissue : Goebel's results led him, as we have seen, to the statement that 

 the spore-producing tissue can be referred as regards its origin to a 

 cell, a cell-row, or a cell-sheet, which can be distinguished very early 

 by the nature of its materials from the rest of the cell-tissue. This 

 archesporium was successfully recognised in certain cases, and the 

 tendency of the time was to expect similar success in all cases. Thus a 

 special significance came to be attached to these cells, quite apart from 

 that of the surrounding tissues, as being predestined from the first to the 

 important function of spore-production. 



The location of the archesporium in the Phanerogams was found to 

 be consistently hypodermal : in a somewhat strained sense the same was 



} Boi. Z:-it., iSSo, p. 545 etc. 



