CYCADALES 



127 



The earliest stages in the development of the strobilus, sporophylls, 

 and ovules have not been studied in any of the genera, even so late 

 a stage as the row 

 of megaspores hav- 

 ing been noted only 

 in Stangeria, Cera- 

 tozamia, a,nd Zamia. 

 In these genera the 

 megaspore mother 

 cell when first rec- 

 ognized was deep- 

 seated in the nucel- 

 lus and surrounded 

 by a mass of cells 

 doubtless homolo- 

 gous wn'th the 

 "spongy tissue" of 

 conifers. In Stan- 

 geria (29) and Cera- 

 tozamia (11) the 

 mother cell gives 

 rise to a row of 

 three cells, and in 

 Zamia (74) to a row 

 of four cells, the 

 innermost of which 

 becomes the func- 

 tioning megaspore 

 (figs. 118-120), the 

 first cell of a new 

 gametophyte. 



There is a single 

 massive integu- 

 ment, and the nu- 

 cellus is free only 



Figs. 118-120. — Megaspores of cycads: fig. ii8, 

 Stangeria paradoxa, showing the functional megaspore 

 enlarging at the expense of two functionless cells of the 

 megaspore row; X250; fig. 119, Ceratozamia longijolia, 

 showing row of three cells, the lowest (functional mega- 

 spore) beginning to enlarge: X266; fig. 120, Zatuia flori- 

 dana, the row of four megaspores. — FiG. 118, after Lang 

 (2g); fig. iiQ, after Treub (ii); fig. 120, after F. (iR.\CE 

 Smith (74). 



for a short distance. 



At the apex of the nucellus, some time before the shedding of 



pollen, a vigorous growth results in the formation of the character- 



