THE GYMNOSPERMAE : CYCADALES, ETC. 



723 



Fig. 727. — Cycas reiohda. Apex of a flowering plant showing the 

 apical cluster of megasporophylls with attached ovules. 



(From the '* National Geographic Magazine.") 



Each sporophyll is 6 to 8 in. long, the upper 

 Uke a leaf, and tapering to a point (Fig. 728). O 

 lateral rows of orange-coloured ovules, appar- 

 ently replacing the pinnae on this part of the 

 organ. The whole structure is covered densely 

 with brownish hairs, but these are lost from the 

 ovules as they ripen. 



Other species of Cycas show traces of pinnate 

 structure in the sporophylls and a reduction 

 series may be arranged starting from Cycas 

 revohita and showing all stages in the modi- 

 fication of the megasporophyll, from a structure 

 in which the semblance of a leaf is still evident, 

 to a short woody structure in which all foliar 

 semblance has been lost, forming part of a cone 

 as closelv built as that of a Pine (Fig. 729). 

 Such a series probably does typify the actual 

 course of evolution of the cone in the Cyca- 

 dales, but it leads into a cul-de-sac, and the 

 ancestors of the Angiosperms probably had more 

 in common with the loose organization of Cycas 

 revohita than with the high specialization of 

 types like Zamia. 



The ovules are the largest in the plant 

 world. Thev increase but little in ripening 

 and may be as large as a hen's egg. They are 

 slightly flattened in the plane of the sporophyll, 

 and this shape corresponds to a dorsiventral 



portion broadly pinnate, 

 n the lower half are two 



IJ^J^' 



Fig. 728. — Cycas reioluta. A 

 single megasporophyll 

 showing pinnate apex and 

 two rows of laterally 

 attached ovules. 



