CYCADALES 



137 



It is probable that this condition is characteristic of the cy- 

 cads, with the barely possible exception of Microcycas. This 

 free nuclear condition is less primitive than that shown by Pinus 

 and some other gymnosperms, in 

 which a wall is formed between the 

 ventral canal nucleus and that of 

 the egg. Caldwell (52) states 

 that in Microcycas there are often 

 two or three free nuclei in the 

 archegonium, and suggests that 

 the extra nuclei may have arisen 

 from the division of the free ventral 

 canal nucleus, but more probably 

 from the fusion of two or more 

 archegonia. From a study of Cald- 

 well's figures, Land (54) suggests 

 that these archegonia are not primi- 

 tive, but are homologous with the 

 multinucleate "archegonial tubes" 

 of Welwitschia, so that the condition 

 would be intermediate between that 

 which prevails in gymnosperms and 

 that which characterizes angio- 

 sperms. The fact that the neck 

 of the archegonium in Microcycas 

 is only feebly developed seems to 

 favor this view. The archegonium 

 situation in Microcycas is shown in 

 figs. 148-150. 



During the early stages in the 

 development of the archegonia there 

 is not only no archegonial cham- 

 ber, but the archegonial region of 

 the gametophyte is slightly elevated. 

 Later, the rim of the elevation grows rapidly, while the growth of 

 the elevation itself is checked, so that what was at first the most 

 elevated portion becomes the bottom of the archegonial chamber 



Figs. 148-150. — Microcycas calo- 

 coma: fig. 148, general view of trans- 

 verse section of endosperm, showing 

 numerous scattered archegonia; X3; 

 fig. 149, archegonium with one nucleus; 

 X7S; fig. 150, archegonia with three 

 nuclei, "probably resulting from the 

 fusion of three archegonia"; X270. — 

 After Caldwell (52). 



