Tf. 



^8 BOTANICAL GAZETTE [jULY 



tion be accepted, then Ophioglossum agrees with the other genera in 

 the origin of sporangium, wall, primary sporogenous cell, and tapetum, 

 This regularity of division is limited to the part of the outer wall 

 which from its position may be inferred to have arisen from the 

 sporangiogcnic band. In other parts of the wall, not only is the 

 division less regular, but the number of layers is greater. Further- 



i 



more, longitudinal sections show that probably this regularity is still 

 further limited to the cells derived from the initial cell (or cells) of 

 the sporangium. 



By the time the sporogenous tissue has reached the mother-cell 

 stage, the wall has its full number of cell layers. The further develop- 

 ment of the wall consists of an increase in size of the hypodermal cells 

 in the tangential plane, without any increase of thickness, and a 

 growth and anticlinal division of the epidermal cells. In mature 

 sporangia the epidermal cells are relatively deep and narrow, with 

 thickened outer walls. Fig. 7, which shows a sporangium at time of 

 dehiscence, may be compared with fig, 6, from a sporangium whose 

 sporogenous tissue had reached the stage of young tetrads. Fig. 7 

 has just half the magnification of fig. 6^ from which it is evident that 

 the epidermal cells have just about doubled their depth, and have in 

 some cases decreased in width through anticlinal division- As 

 already remarked, the hypodermal cells do not increase in thickness, 

 but become extended laterally as the sporangium enlarges. From 

 about the time the young spores begin to round up, they gradually 

 lose their cell contents and become flattened as growth of the sporan-. 

 gium progresses. Sooner or later the walls of the inner two or three 

 layers, and often all the hypodermal layers, disappear. In fig. 7 

 portions of the walls of two layers can be traced, but in other cases the 

 only remains consist of a line of debris between the spore-mass and 

 the epidermis. 



At the earliest stage examined, the wall cells contain considerable 

 starch, which increases up to the time the wall has attained its full 

 number of cell layers. After this, which is about the time the tapetal 

 Plasmodium invades the crevices of the sporogenous tissue, it gradually 

 wastes away, until none at all is present at time of dehiscence. Its 

 disappearance may be connected with the accumulation of starch in 

 the tapetal plasmodium, a matter which will be discussed subsequently. 



