408 A TEXTBOOK OF GENERAL BOTANY 
Cycas the megasporangia also occur in a cone (Fig. 462) at the 
apex of the stem. In the genus Cycas the megasporophylls are 
not in cones (Fig. 455) and are somewhat similar to ordinary 
leaves (Fig. 457). They are produced at the tip of the stem in 
whorls alternating with whorls of ordinary leaves (Fig. 455). The 
megasporophylls of Cycas revoluta are very leaflike in appearance 


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Fig. 457. Megasporophylls of cycads 
Left, Cycas revoluta with young ovules (x 2); second figure, Cycas circinalis. 
with young ovules (x 2) ; third figure, Cycas rumphii with seed (x 2). This 
species usually bears six ovules, but two or four are also frequent. Upper right, 
Diodn edule with seed (x 2); lower right, Zamia with seed (x 4) 
(Fig. 457), while those of the genus Zamia bear almost no resem- 
blance to ordinary leaves (Fig. 457). Between these two extremes 
there are various gradations (Fig. 457). The leaflike appearance 
of the megasporophylls of Cycas revoluta indicates that they have 
been derived from ordinary spore-bearing leaves, while the era- 
dations between the megasporophylls of Cycas revoluta and those 
of Zamia indicate that even the highly modified sporophylls of 
Zamia had a similar origin, 


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