DOUBLE NUMBER. 
VOL. XIX, Nos. 7 & 8. July & Oct., 1920. 
[Published August 24th, 1920.] ^ 
THE 
NEW PHYTOLOGIST 
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: 
HYBRIDISM AND CLASSIFICATION IN THE GENUS ROSA. J. R. Matthews . 
MUTATIONS AND EVOLUTION, Chapter VI. R. Ruggles Gates. 
THE MECHANISM OF ROOT PRESSURE. [With Two 
Figures in the Text] « - - - - - - /. H. Priestley. 
METHODS AND SIGNIFICANT RELATIONS IN THE CC. West, G. E. Briggs , 
QUANTITATIVE ANALYSIS OF PLANT GROWTH \ and F. Kidd. 
PRELIMINARY NOTES ON ADDITIONAL EVIDENCE FOR 
THE HYDRION DIFFERENTIATION THEORY OF 
GEOTROPISM 
I. On the Reversal of Gjsotropic Curvature in the 
Stem - - - - - - - - - J. Small & M. W. Rea. 
II. On the Angle of Balance in Roots, Stems and 
Leaves - JSmall & M . /. Lynn. 
III. A Theory of the Origin of Leaves - - - J. Small. 
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