SCIENCE— ADVERTISEMENTS 



NEW BOOKS 



KEW 

 Cretaceous and Cenozoic Echinoidea 

 of the Pacific Coast 



133 Pages, 40 Plates, Paper $2.50 



SWARTH 

 Revision of the Avian Genus 

 Passerella 



149 Pages Paper $1.75 



ALLEN 

 Plankton of the San Joaquin 

 River 



292 Pages Paper $3.00 



Carriage Extra 



The University of California Press 



Berkeley, California 



19 Eait 47th Street, New York 



Journal 



of the 



Optical Society of America 



The Journal of the Optical Society of America 

 is a bimonthly publication devoted to all branches 

 of Optics. 



The current number of 164 pages contains 

 sixteen articles on lens design, photography, 

 colorimetry, optical glass, etc. 



The Journal is sent free of charge to members 

 of the Optical Society of America. The Subscrip- 

 tion rate to non-members and to libraries is $5.00 

 per year. 



The unexpected demand for back numbers has 

 depleted the supply of certain issues. Libraries 

 desiring the complete issue for 1920 should place 

 order immediately. 



New contributors to the Journal are hereby 

 informed of the Editorial Policy of this Journal 

 which insures prompt publication of all accredited 

 short papers in optics. 



For further information address 



PAUL D. FOOTE, Editor 



Bureau of Standards 

 WASHINGTON, D. C. 



Blakiston 



GAGER 



Evolution and Heredity 



in Plants 



A concise, well-illustrated 

 textbook and guide for 

 beginning students, and 

 more general readers. 



By C. STUART GAGER 



Director Brooklyn Botanic Garden 



113 Illustrations, 12nio. Cloth $1.25 

 Postpaid 



P. Blakiston's Son & Co. 



PUBLISHERS PHILADELPHIA 



THE 

 BAHAMA FLORA 



Nathaniel Lord Britton 



Director-in-Cliief of the New Yort Botanical Garden 

 AND 



Charles Frederick Millspaugh 



An octavo volume of 695 pages 

 Published by the authors 



Copies may be obtained from 



Mr. G. K. Ackerman 



Lorillard Mansion 



Bronx Park New York City 



Price $6.S5, which includes posta 



