292 DR. LILY BATTEN ON 
It is evident that the Polysiphonia has obtained food from the dark cells, 
and also there seems no other explanation of the need for the ‘swollen thin- 
walled tip of the rhizoid, which applies itself so closely to the host cells (see 
page 277 et seq.). 
It is not absolutely necessary for the life of the Polysiphonia that it should 
be fixed to any host, but on the rare occasions when it occurs on a rocky 
substratum its vegetative growth is less perfect, although external conditions 
are similar with respect to depth and general environment. This shows that 
a direct advantage is gained by an epiphytic habit, and the statement is 
amplified by an examination of the anatomy. 
There is frequently a slight local modification of the cells of the host in 
the immediate vicinity of the penetration of the Polysiphonia. Sometimes a 
little swelling occurs, and very frequently the cortical cells are displaced so 
that they no longer occur in chains. 
Habitat. Occurring chiefly on Ascophyllum nodosum, but occasionally 
found on Fucus serratus and Fucus vesiculosus. It rarely occurs on a rocky 
substratum. Common. 
British Records. Very common on the shores of the British Islands where- 
ever its host-plant, Ascophyllum nodosum, grows. 
Distribution in Europe. Atlantic shores and Baltic Sea. 
3. P. FURCELLATA Hook. in Smith’s English Flora, v. 1833, p. 332. 
P. forcipata J. G. Ag. Alg. Med. 1842, p. 127. 
Reference. Agardh (2) ii. p. 1025. 
Icones. Harvey, Phye. Brit. pl. 7. syn. 126. Johnstone & Croall, 
Nat. print. Brit. Seaweeds, pl. 221. 1859. Kützing, Tab. Phye. xiii. 
p. 25, tab. 79, 1863. Ewsiecatr. Crouan, Alg. mar. Finist. no. 306, 1852. 
Lloyd, Alg. Ouest Fr. no. 230, 1854. 
DESCRIPTION.— Habit. Plants 12-14 cms. in length, with a well-marked 
central axis and numerous lateral branches. Main branches arising 
alternately with very wide axils, smaller branches and ramuli showing 
marked pseudo-dichotomy, apices being eventually clad with clusters of 
fibrillæ. Siphons. 8 or 9 pericentral round small central. Colour. Brick- 
red when fresh, becoming much darker in the herbarium. Anatomy. 
Length of artieulations 3-5 times their breadth in the main branches, 
diminishing in the smaller branches, and only equal to their breadth in the 
ramuli. Reproductive organs. Tetraspores are intercalary in development, 
and are borne in distorted ramuli.  Cystocarps are ovate and sessile. 
Antheridia are borne in clusters at the tips of the ramuli. 
P. ceramivformis Crouan appears to have been assigned to a young form 
of P. furcellata, which is perhaps nearest to P. furcellata a. forcipata Ag. 
(2) ii. p. 1025. The articulations in this form are shorter than those of 
P. furcellata, and the siphons number eleven or twelve. 
Habitat, Usually recorded either dredged or floating. Rare. 
