1 68 THE LIVING CYC ADS 



Bennettitales or developed directly from the Cycado- 

 filicales cannot be determined until we know more about 

 the extinct forms of the lower Mesozoic. The university 

 zone of the Northern Hemisphere has been studied with 

 considerable care, and the amount of Triassic material 

 obtained has not been encouraging; but the tropics and 

 Southern Hemisphere may yield material which will 

 solve the whole problem. The immense amount of 

 fossil material secured by Wieland in the Mixteca Alta 

 of Southern Mexico, although not in a condition to be 

 sectioned, leads us to hope that the missing Hnks will be 

 discovered. 



For many years the author has been preparing a 

 much more extended technical account of the living 

 cycads. The work has been delayed by the more im- 

 portant work of these imperative times, but, when com- 

 pleted, we hope that the results will be of interest to those 

 who are investigating the evolution and phylogeny of 

 the gymnosperms. 



