Vol. XX, No. 4 
November 2, 1921 
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 
A Study of some of the Factors Controlling the Periodicity of Freshwater 
Algse in Nature. By William J. Hodgetts, M.Sc. (With 3 figures 
in the text).150 
Thalassiophyta and the Algal Ancestry of the Higher Plants. By F. E. 
Fritsch .165 
The Study of Human Implements as an Aid to the Appreciation of 
Principles of Evolution and Classification. By E. J. Salisbury . . 179 
WHELDON & WESLEY, Ltd. 
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