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- 

 iozamia, and 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 with 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. 1 18-120), the 

 first cell of a new 

 gametophyte. 



There is a single 

 massive integu- 

 ment, and the nu- 

 cellus is free only 

 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- 



FiGS. 118-120. — Megaspores of cycads: fig. n8, 

 paradoxa, showing the functional megaspore 

 enlarging at the expense of two functionless cells of the 

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

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

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

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

 (29); fig. 119, after Teeub (ii); fig. 120, after F. Grace 

 Smith (74). 



