428 G. B. Wieland — American Fossil Cycads. 



As now understood, however, in Cycadeoidea dacotensis 

 Macbride, C. Marshiana Ward, and several other species, 

 moncecism is indicated. In the series of species which includes 

 Cycadeoidea (or Bennettites), Gibsonianus, Morierei, and 

 Wielandi, there is every probability of dioecism. While in 

 the forms immediately ancestral to those under discussion, and 

 as now seems possible, including Cycadeoidea etrusca, it is 

 probable that the fructifications were potentially bisporangiate 

 and had continued so from far back towards the time when 

 ancestral Marattiacese attained heterospory. It is hence not 

 unlikely that within the next few years all these forms of 

 fructification will be found very definitely exhibited in cycadean 

 forms of the Mesozoic. 



The description of the expanded flowers with complete 

 restorations of typical forms of these cycads in full leaf and 

 fruit, all the details for which are now at hand, being reserved 

 for the final publication, it remains to consider briefly the 

 microsporophylls, or staminate fronds, and also to present cer- 

 tain general conclusions based upon their structure and strobilar 

 association. 



The Staminate Fronds. 



As has been explained above, the most fundamental feature 

 of the bisporangiate strobilus is a staminate or pollen-bearing 

 frond. The petiole of each frond, as seen in unexpanded stro- 

 bili which have begun to emerge from the surrounding leaf 

 bases, and which bear approximately mature pollen, is about 

 10 centimeters in entire length as folded back once adaxially 

 along the central ovulate axis. The pinnules inserted on all 

 that portion of the petiole as seen to rise and then curve inwards 

 to form a member of the still folded group, are simple, very 

 thickly set with synangia in nodes, and folded back in closely 

 appressed drooping pairs towards the axis of the receptacle, 

 between the ascending and descending segments of the petiole. 

 (See figure 1.) But on the upper portions of the frond as 

 seen in this infolded position, or inflexed prefloration, turned 

 downward and lying closely appressed to the surface of the 

 central ovulate cone, the pinnules lie in an outwardly and then 

 more and more upwardly directed position, though of course 

 becoming more and more inconspicuous towards the tip of the 

 frond. And it is also a very interesting fact that the upper 

 portion of the petiole is at first much compressed laterally, but 

 as the tip is approached becomes expanded into a broad lamina 

 much as in the ovulate fronds of Cycas. Of the pairs of sim- 

 ple pinnules there are about twenty, including the abortive and 

 smaller ones near the base of the frond as well as those near the 

 tip, the first and last fertile ones bearing but a single synangium. 



