THE EVIDENCE 91 



well suggested that each pair of pollen-sacs may 

 correspond to a synangium of Bennettites, 

 with its double row of compartments. In a 

 few Angiosperms (Mimosa, for example), similar 

 compartments exist. But have we any evidence 

 of a transition from the complex Bennettitean 

 stamen to the simple Angiospermous type? A 

 fossil recently found by Dr. Wieland in the 

 Upper Trias of the Mixteca Alta in Mexico 

 helps to bridge the gap. These beds are ex- 

 traordinarily rich in remains of Mesozoic Seed- 

 plants, especially Williamsonia, a genus which 

 has been known since the early part of the last 

 century, when Zamia gigas (now Williamsonia 

 gigas} was first discovered in the Yorkshire cliffs. 

 The flowers of Williamsonia (unfortunately pre- 

 served only as casts) have been repeatedly 

 investigated, and it has now been established that 

 both male and female organs were essentially of 

 the same type as in Bennettites. It appears, 

 however, though this is not perhaps quite certain, 

 that in Williamsonia there were distinct male and 

 female flowers. 



Now in Dr. Wieland's Mexican specimen, 

 which he calls the El Consuelo Williamsonia, 

 from the quarry where it was found, there is a 

 ring of stamens, united below into a bell-shaped 

 tube, only the upper parts being free. The 

 point of interest is that the stamens instead of 



