Foreword 



This publication is a continuation of the NATIONAL 

 ARBORETUM CONTRIBUTION series. CONTRIBU- 

 TION No. 1, "Annotated List of the Plants Growing 

 Naturally at the National Arboretum," by Oliver M. 

 Freeman, was published in August 1953. 



The CONTRIBUTIONS will be serially numbered. 

 Subject matter will include the results of basic and ap- 

 plied research on cultivated and wild plants, reports on 

 plant explorations and introductions, and compilations 

 and checklists of value to horticulturists. 



The continuation of the CONTRIBUTIONS provides 

 a significant opportunity for the further communication 

 of information for the advancement of horticultural and 

 botanical science. 



Director 

 National Arboretum 



