ON THE GENUS POLYSIPHONIA. 271 
The Genus Polysiphonia, Grev., a critical Revision of the British species, 
based upon Anatomy. By Lity Barren, M.Sc., Ph.D. (Communicated 
by Prof. Dame HELEN GwysxE Vauauay, D.B.E., D.Sc., F.L.S.) 
(PLATES 22-25.) 
[Read 14th December, 1922. | 
THE object of the following paper is to work through critically the British 
species of Polysiphonia, but at the same time to investigate thoroughly their 
organs of attachment. An attempt having been made to collect material 
from various localities, the neighbourhood of Swanage was finally decided 
upon as the special area for purposes of this paper, a series of visits being 
subsequently made at different times of the year. The nature of the rock 
and tilt of the strata was found to influence the distribution of marine alge, 
even if one only considers the mechanical action of the water. The area 
chosen is very varied geologically, so that species can be found which need 
sheltered bays for their habitation, as well as those which are able to persist 
on rocky headlands exposed to the full force of the tide. Studland is a 
sheltered bay, eroded in sandy Tertiary beds. It is not only valuable for its 
own flora, but for the numbers of specimens which are washed into the bay 
after rough weather. West of Ballard Down the Wealden is exposed, the 
beds consisting of sand and clays, while between Durlston Head and 
St. Alban’s Head the Portlandian forms the coast-line, 19 feet of Portland 
stone forming the base of the cliffs in Durlston Bay. The mud flats of 
Poole Harbour form another type of hunting-ground, where local conditions 
cause marked variability in the form of certain species. In the marine lake 
of Poole Park a floating form of P. vartegata has been found and given to 
me for description by Mr. A. D. Cotton. Between the Haven, at the 
entrance of Poole Harbour, and Sandbanks, a number of groins run out into 
the sea, and these are particularly rich in some of the smaller Polysiphonias. 
Material which can only be obtained by dredging has been sought after at 
Plymouth from the * Oithona,’ belonging to the Marine Biological Station, 
and useful shore-collecting for individual species has been done near 
Wembury and on the island off Looe, as well as at Ilfracombe, Torquay, and 
near Berry Head. A few rare species which it was not possible to obtain 
by collecting have been examined at the Royal Botanic Gardens, Kew, the 
Natural History Museum, South Kensington, and in the herbarium of 
Mrs. Griffiths at Barnstaple. 
Former systematic descriptions of the group have been worked through 
critically, attention having been paid to the general detailed anatomy of the 
