1907] BURLINGAME— SPORANGIUM OF OPHIOCLOSSALES 37 



THE WALL 



Owing to the conflict of opinions^ the youngest material at hand 

 was examined for evidence of the origin of tapetum and sporogenous 

 tissue- These sporangia have a wall three cells thick, or in some 

 cases the spindle and beginning of the wall between the middle and 



innermost cell. Fig. i shows the next stage, where the wall is three 

 or four cells thick. WHiere the wall is four cells thick and the position 

 of the walls indicates the last one formed (wall i in the figure), the 

 division is seen to have occurred in the outer cell of the three-layered 

 wall. The fifth layer of cells also arises in a similar way by the 

 division of the cells of the outer layer of a four-layered wall (figs, 2 



i 



and J, wall i). This is made clearer by an examination of the cell 

 row between the two containing five each in fig, 2. It may be seen 

 that the next division will occur in the outer cell. 



The order of development may be stated in the reverse order as 

 follows: If the cell layers be numbered from within outward j, 2, j, 

 4^ 5, then 5 and 4 arose from the division of a cell which we may call 

 c. In like manner c and j arose from the division of a cell h. As 

 already pointed out, i and 2 arose from the division of a cell a. The 

 tapetum is already formed and differentiated at the two-layered stage 

 of the wall, so that two suppositions may be entertained in regard to , 

 the early history of the wall. First, a and h may have been derived 

 from the division of a cell w, sister to the tapetal cell. Second, cell a 

 and the tapetal cell may be sister cells derived from the division of a 

 cell sister to h. Of these two suppositions, both of which assume 

 the tapetum to have oriprinated from the wall, the former seems the 



more probable. That the tapetum does arise from the wall seems to 

 be indicated by the close similarity of its cells in shape and position 

 to the tabular wall cells and their contrast to the polygonal sporoge- 

 nous cells. In the very earliest stages observed it is difficult to 

 distinguish tapetal cells from wall cells except by position, though the 

 sporogenous cells are easily distinguishable in almost all cases. It 

 is not unlikely that the first division of the cell (or perhaps cells) of 

 the sporangiogenic band is a periclinal one and separates the primary 

 sporogenous from the primarj^ wall cell. A periclinal division of the 

 latter separates the primary tapetal cell from the wall cell, subsequent 

 divisions of which produce the five-layered wall. If this interprera- 



