Sarah M. Baker. 
196 
time, this does not explain the maintenance of an enormous 
maximum through the cold period (4 n —1°C) when in both the pre. 
ceding years the greatest maximum was attained at a temperature 
of approximately 9 n C. 
Botanical Laboratory, 
Birmingham University. 
ON THE CAUSES OF THE ZONING OF BROWN 
SEAWEEDS ON THE SEASHORE. 
By Sarah M. Baker 
(University College , London). 
[Text-Figs. 27—30]. 
HE conditions which determine the zonal growth of Algae 
between the tidal limits appear likely to be very simple, and 
thus afford a very promising field for experimental study. The 
present paper is a contribution in this direction. The actual zonal 
distribution of Algae on the shore has been very thoroughly studied 
by Borgesen,’ and others. But in order to have a clear under¬ 
standing of the conditions under which the seaweeds were growing 
at the particular locality chosen for the present work, a set of 
measurements was taken to find their vertical distribution in 
relation to the tides. The experiments were carried out on the 
eastern side of White Cliff Bay, near Bembridge, Isle of Wight, 
where there is a continuous stretch of gently inclined limestone and 
marl rocks upon which the Algae grow profusely, for a distance of 
about two miles along the coast. 
The level of high water at the spring tide was found by marking 
from a boat the highest point to which the tide rose on a given 
rock. This point was used as the standard point of reference. At 
low tide an observer was stationed at this rock, while two others 
went down and found the seaweeds. The vertical distance below 
1 Borgesen. Om Alge-vegetationen ved Faeroernes Kyster. 
Gyldendalske Boghandel, Nordisk Forlag. Kjobenhavn et 
Kristiania, 1904. Also Idem. The Algal Vegetation of the 
Faroese coasts, with remarks on the phyto-geography. 
Botany of the Faroes based on Danish investigations. 
Copenhagen,1905. 
