PREFACE vii 



and to Miss Eloise Gerry, of the United States Forest Service, 

 an admirable photograph elucidating the "bars of Sanio" in 

 coniferous wood. Last but not least, the author records the 

 valuable services of Mr. James Austin, assistant in the labora- 

 tories, in connection with the preparation of the numerous photo- 

 graphic illustrations. Dr. D. H. Scott and his publishers, Messrs. 

 A. and C. Black, have very kindly permitted the reproduction of 

 a number of figures from the admirable Studies in Fossil Botany, 

 which are among the comparatively few illustrations in the present 

 work which are not original. To Dr. R. T. Jackson the author 

 is indebted for the opportunity of photographing for illustration 

 a number of the sections of carboniferous plants under his care 

 in the Botanical Museum. 



Professor John M. Coulter has been good enough to read the 

 proofs as the present volume passed through the press. To my 

 friend Mr. R. W. Sayles, Director of the Geological Museum, I 

 am indebted for valuable criticisms in the field of paleoclimatology 

 and also for other essential aid. The author is alone responsible 

 for the views expressed and for any errors. 



BOTANICAL LABORATORIES, HARVARD UNIVERSITY 

 June, 1917 



