1907] BURLINGAME—SPORANGIUM OF OPHIOGLOSSALES 39 



Longitudinal sections (figs. 6 and 7) show the method of dehis- 

 cence. About the time the young tetrads are forming, each sporangium 

 j shows a slight transverse groove. Fig. 6 shows that this corresponds 



to a band of smaller thin-walled cells. The groove becomes 

 more pronounced through the failure of the epidermal cells along it 

 to increase in depth as fast as the neighboring ones. Finally a rupture 

 of the sporangium occurs along this groove, probably due to strain 

 set up by unequal growth. The spores are shed through this slit, 

 which, so far as the material at hand indicates, seems to play a purely 

 passive role in the process. 



I 



^ 



i 



► 



\ 



THE TAPETUM 



The youngest stage of the tapetum observed is shown in fig. i. 

 That this probably originates from the first periclinal division of the 

 primary wall cell has already been pointed out. It divides periclinally 

 once (sometimes oftener, as shown in fig. 5), before the cells of the 

 sporogenous tissue have reached the mother-cell stage. Usually no 

 more strictly periclinal divisions occur. As the sporangium grows, 

 the tapetal cells elongate and divide obliquely {figs. 2, j, 5). Fig. 3 

 presents a regional view of about one-half of a sporangium with the 

 tapetum well developed and distinct at the left of the figure, where it 

 • "flay be supposed to be derived from the primary wall cell. At the right 



of the figure the tapetal cells are not easily distinguished from the 

 sporogenous tissue, and their origin is not clearly indicated, though 

 they seem rather more closely related structurally to the sporogenous 

 cells than to the sterile cells around them on the outside. In Botr>xh- 

 ium GoEBEL has shown that this part of the tapetum arises from 

 the sterile cells outside the archesporium. In the present study no 

 clear evidence for either view was obtained, owing to lack of young 



sporangia 



observed 



^i lilt; earnest ot)served stage tne tapetai ceiis are uibnnguisnauxi, 

 from the sporogenous tissue by staining reactions of the cell contents 

 and by the position of the walls. They are less easily distinguished 

 from the wall cells, but are on the whole slightly thicker radially. 

 The cytoplasm is clear and highly vacuolate and so takes the stain 

 lightly. It does not contain starch nor any form of stored food 



In this respect it differs from the 



microscope 



