CYC AD ALES 157 



one of them is the strobilus of a heterosporous lycopod, which he has 

 named Lycostrobus. Scott (69) regards the evidence of the existence 

 of mesozoic cycads on the basis of staminate strobili as not convincing. 



The testimony from ovulate strobili is more definite. The evidence 

 of Zamia-like forms is unsatisfactory, but megasporophylls like 

 those of Cycas are recorded from various strata of the Mesozoic, in 

 one case with a seed attached. While the occurrence of Cycas-like 

 forms seems to be established, Nathorst (55) has found that the 

 pinnae of several of them contain double vascular bundles, rather 

 than the single one of the living Cycas, and for these he has proposed 

 the genus Pseudocycas. 



Fragments of the vegetative structures cannot be used to differen- 

 tiate Cycadales and Bennettitales, so that strobili are essential and 

 these must be well preserved. In summing up the evidence for the 

 existence of mesozoic cycads, therefore, Scott (69) says that the 

 whole question "is in an unsatisfactory condition and the evidence 

 is singularly meager." 



In view of the above statements, it is evident that there are no 

 facts as to the distribution of mesozoic cycads. That they were widely 

 distributed may be inferred from their relationship to the Bennettitales, 

 from the increasing abundance of cycads in more recent deposits, 

 and from the present distribution of the group. The distribution 

 of the living cycads has been stated at the first of the chapter. 



6. Relationship to other gymnosperms 



The relationship of Cycadales to Bennettitales and Cycadofilicales 

 is the only one that needs consideration, since the other gymnosperm 

 groups can be connected with it only by way of the Cycadofilicales. 

 Under Bennettitales (p. 86) this subject was discussed somewhat in 

 detail, and little need be added here. 



That Cycadales are connected with the Bennettitales in origin 

 seems clear; in fact, no two great gymnosperm groups have so many 

 features in common. The transition from the trunks of Cycadeoidea, 

 with their numerous lateral strobili, through such a form as Wil- 

 liamsonia gigas, with its several strobili appearing from the center 

 of a crown of leaves, to the cycads, with a usually solitary and ter- 

 minal strobilus, seems natural, and suggests that the Cycadales are 



