DOUBLE NUMBER. 
VOL. XIX, Nos. 3 & 4. March 
[Published May 18th, 1920.] I : ' J 9 1920 
THE 
A BRITISH BOTANICAL JOURNAL, 
EDITED BY A. G. TANSLEY, M.A., F:R.S. 
UNIVERSITY LECTURER IN BOTANY, CAMBRIDGE, 
IN CONSULTATION WITH THE STAFF OF THE CAMBRIDGE BOTANY SCHOOL * 
Contents: 
A THEORY OF GEOTROPISM: with somk experiments 
ON THE CHEMICAL REVERSAL OF GEOTROPIC RESPONSE 
IN STEM AND ROOT [WITH PLATE I AND FlVE FIGURES 
in the Text] . . James Small: 
MUTATIONS AND EVOLUTION. Chapter II— contd. and III R. Ruggles Gates . 
WHAT IS THE SIGNIFICANCE OF THE EFFICIENCY ( Franklin Kidd, 
INDEX OF PLANT GROWTH ? [With Two Figures ] Cyril West and 
IN THE Text] - - - - - - - ( G. E. Briggs. 
THE SIGNIFICANCE OF THE EFFICIENCY INDEX OF 
PLANT GROWTH.- - - V. H, Blackman . 
PUBLISHED MONTHLY OR BI-MONTHLY - (EXCEPT AUGUST AND 
SEPTEMBER). 
WILLIAM WESLEY & SON, 
28 Essex Street* Strand,|W.C.2. 
LONDON. 
Subscription-Price, One Pound per annum (ten numbers) post free.' 
PRICE OF MONTHLY NUMBER - HALF-A-CROWN. 
PRICE OF BI-MONTHLY NUMBER - FIVE SHILLINGS. 
