CYCADALES 



17 



mother cell, which closes the history of the sporophyte in this 

 direction, and later through a reduction division begins the 

 gametophyte generation. 



Lang observed in Stangeria that about this mother cell 

 and its product a persistent layer of the sporogenous tissue 



FIG. 14. Cycas rerohita, ovulate sporophyll ; 

 one half natural size. From photograph 

 taken in Washington Park, Chicago. 



FIG. 15. Dioon edule, ovulate sporo- 

 phylls from strobilus shown in Fig. 

 12; one half natural size. 



organizes, apparently functioning as a tapetum. Whether a 

 definite layer be organized or not, the adjacent cells continue 

 to contribute nutrition to the mother cell and its functioning 

 spore. 



During these changes in the sporogenous tissue, the apex of 

 the nucellus develops a more or less prominent beaklike process 

 which projects into the micropyle (Fig. 17). The cell walls 

 in this beak region become firm, and the whole structure forms a 

 persistent cap, very noticeable in Cycads, in GinJcgo, and in 

 such fossil forms as the Cordaitales and Bennettitales. Within 

 this firm beak the pollen chamber is organized, which may be 

 narrow or broad, but in any event is able to contain numerous 

 pollen grains, one or two dozen having been observed in a single 

 pollen chamber of Zamia. 



