CYCADALES 



17 



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

 direction, and later through a reduction division hegins the 

 garnetophyte generation. 



Lang ol)served in ,^tartger{a that al.ont this mother cell 

 and its product a persistent layer of the sporogenous tissue 



Flo. 14. — f '//I'l'.^ r> rnh.ita, ovulate pporophyll : 

 ODo lialf natural hize. — From photogra})li 

 taken In ^VasIlin;^ton Park, (.'hica;jo. 



Fig. 15. — I-Hoon gduh^ ovulate sporo- 

 pliylls from stroliiluB shown in Fig. 

 I'J; one half natural ^ize. 



organizes, ajiparently functioning as a tapetum. AVhether a 

 definite layer he organized or not, the adjacent cells continife 

 to contri1:>ute 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 heaklike process 

 Avhich projects into the mieropyle (Fig. 17). The cell walls 

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

 persistent cajj, very noticeable in Cycads, in Ginl'go, and in 

 such fossil forms as the Cordaitales and Bennettitales. AVithin 

 this firm lieak the pjullen chamber is organized, which may be 

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

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

 pollen cliamlier of Zamia. 



