PREFACE 19 



assistance in contributing a large number of English Wealden plants 

 for comparison, and Professor Yokoyama of Tokio kindly forwarded 

 Japanese material of Onychiopsis. Dr. Albert Mann of the Department 

 of Agriculture and Doctors F. H. Blodgett and W. Ralph Jones have con- 

 tributed photo-micrographs or camera lucida drawings. 



The U. S. Geological Survey has cooperated in furnishing a large 

 number of the illustrations and in various other ways. 



Finally any student of Lower Cretaceous floras must acknowledge his 

 great indebtedness to previous workers who have contributed to our 

 knowledge of these floras, more especially to Professor Seward in 

 England, the late Marquis Saporta in Portugal, the late Professor Os- 

 wald Heer in the Arctic regions, and Professors Ward and Fontaine in 

 this country. 



