164 



MORPHOLOGY 



rogenous cell (fig. 388). The three uppermost segments and the cap 

 develop the wall of the capsule, which is only one layer of cells thick. 

 At the junction of the cap cell with the last segment is developed the 

 stomium, which is a group of cells so arranged as to permit a cleavage in 

 the wall of the capsule when it begins to dehisce. The annulus is a 



FIG. 386. Leaflet of Marattia, showing dichotomous venation and synangia 

 (instead of sori). 



band of thick- walled cells which extends from the stomium over the 

 top of the capsule and down on the other side to the stalk (figs. 385, 



390). 

 The primary sporogenous cell cuts off a sterile cell from each one of 



the four faces, these four cells developing the tapetum (figs. 388, 389). 



The centrally 

 placed sporoge- 

 nous cell then be- 

 gins a series of 

 divisions until 16 

 mother cells are 

 38? 7 / ' 1 388 389 ) V"^ formed, which 



FIGS. 387-389. Sporangium of one of the Polypodiaceae : means a maximum 



387, early stage, in which the outer papillate cell has begun to O utDUt of 6 A 

 form the apical cell; 388, later stage, in which the cap cell and 



upper segments invest a central cell (primary spermatogenous), Spores, bometimes 



which has cut off one tapetal cell; 389, later stage, in which all there are only 8, 



the tapetal cells have been cut off and have begun to divide; the even 

 central cell, by a series of divisions, forms 16 mother cells. 



mother cells. The 



tapetal cells break down, leaving the mother cells free in the enlarged 

 cavity (fig. 390). 



These two kinds of sporangia, one from each extremity of the fern 

 series, indicate not only a passage from the eusporangiate to the lepto- 

 sporangiate habit, but also a striking reduction in the output of spores 

 per sporangium. In this latter feature there is complete intergrading 

 through the intermediate families. 



