PTEROPSIDA 



147 



with highly dissected polycycUc dictyosteles, yet all are aUke 

 in the early stages of development of the sporangium. This, 

 together with its stalk, arises from a single cell. The first 

 division of the initial cell (Fig. 22O) is into an apical cell (i) 



Fig. 22 



Development of gametangia and sporangia as found in lepto- 

 sporangiate ferns, a, typical gametophyte. b-h, stages in develop- 

 ment of antheridium (diagrammatic), i, dehiscing antheridium. 

 J, antherozoid of Pteridium. k-n, stages in development of 

 archegonium. o-s, stages in development of sporangium of 

 Polypodium 



(1, apical cell; 2, basal cell; 3, jacket cell) 



(a, k-n, o-s, after Foster and Gifford; b-h, Davie; J, Sadebeck) 



and a basal cell (2). Further divisions take place in each 

 (Fig. 22P) and give rise to a primary sporogenous cell 

 (shaded in Fig. 22Q) and a jacket cell (3). The former gives 

 rise to a two-layered tapetum and to a number of spore 

 mother cells, surrounded by a sporangium wall one cell 

 thick. Further details of sporangium development differ 

 according to species, for some have a long slender stalk, 

 only one cell thick, while others have a short and relatively 



