xxxvn] 



WILLIAMSONIA 



459 



epigynous as in V actinium. This view does not exclude the 

 possibility of the existence of unisexual flowers in some species, 

 but the evidence in favour of a separation of the sexes is by no 

 means decisive. Another difficulty is the absence of protective 

 bracts in the case of the microsporophylls, a striking contrast 

 to the bract- enclosed ovulate strobili of Williamsonia or to the 

 bract-covered flowers of Cycadeoidea. Were the microsporophylls 

 borne on a separate axis general considerations would lead us to 

 expect the association of bracts with the essential organs. The 



\J 



A B 



FIG. 565. A, Williamsonia spectabilis, microsporophyll ; B, W. whitbiensis, section 

 of sporophyll ; C, W. mexicana. ( A, B, af ter Nathorst ; C, after Wieland.) 



fact that no such association has been recorded is a fact favourable 

 to the view that the flowers were bisporangiate. 



The student is warned that the opinion expressed with regard 

 to the position of the microsporophylls is contrary to that 

 which is held by several palaeobotanists 1 . 



Williamsonia mexicana Wieland. 



This species is one of the numerous types discovered by 

 Wieland in Mexico 2 . It is distinguished by the deep campanulate 



1 In addition to the papers already quoted, reference should also be made to 

 Thomas (15 2 ). 



2 Wieland (09) p. 430 (the species is here referred to as the 'El consuelo 

 Williamsonia'); (11) p. 461, fig. 17 C. 



