THE GENUS POLYSIPHONIA. 305 
3. P. FRUTICULOSA Sprengel, Syst. veg. vol. iv. 1825, p. 350. 
Rytiphlea fruticulosa Harv. Phye. Brit. pl. 220. syn. 105. 
FHutclinsia. Wulfeni C. A. Ag. Sp. Alg. vol. ii. 1828, p. 95. 
Grammita Wulfeni Bonnem. Hydroph. loc. 1822, p. 27. 
P. Martensiana Kütz. Tab. Phyc. xiv. 1864, p. 10, tab. 29 (a-e). 
P. pyenophlea Kütz. l.c. p. 10, tab. 30 (e-g). 
P. comatula Kütz. l. e. p. 10, tab. 31 (a-e). 
References. Agardh (2) ii. p. 1028 ; De Toni (22) iv. p. 950. 
Icones. Harvey, Phye. Brit. l. e. Kützing, Tab. Phyc. l.c. Falkenberg, 
Die Rhodomel. 1901, pl. 21 (1-5). Eirsiecata. Wyatt, Alg. Damnon. no. 132. 
DesCRIPTION.— Habit. Occurring in tufts from 10-15 cms. in height. 
Branching roughly pseudo-dichotomous in the main branches, with wide 
angle of divergence causing characteristically angular appearance. Smaller 
branches bi-pinnate, the whole plant being elothed with short spine-like 
ramuli set at a wide angle. Perennial species, cartilaginous in nature. 
Siphons. 8-12 pericentral, surrounded by a wide band of corticating 
cells. Colour. Dark brownish-purple. Anatomy. Articulations almost 
completely obscured throughout the plant by the corticating cells. When 
visible they are about as long as broad, except in the small branches and 
ramuli where their length is less than their.breadth. Attachment organ. 
Rhizoids developed from siphons and corticating cells at the base of the 
original axis. Later, branches arising near the base creep along the sub- 
stratum and bear laterals alternately, those on the upper side forming ‘shoots,’ 
the lower ones being modified to form attachment organs. The modified 
branches bear rhizoids profusely, frequently strengthening the holdfast by 
twisting round a portion of the coralline host. Reproductive organs. Tetra- 
spores borne in swollen and distorted ramuli. Cystocarps rare, sessile and 
ovate in form when present, crowded on the ramuli. 
The attachment organ of this species is of especial interest, resembling 
that of Pterosiphonia rather than Polysiphonia. It is the only British 
member of the latter genus which has branches specially modified to form 
attachment organs. 
Habitat. Occurring in tide-pools on the rocky bottom, and particularly in 
warm shallow pools on Corallina officinalis and other coralline alge. 
Occurring also in the low littoral zone when the Fucus serratus vegetation is 
not too dense. Common on the shores of the South of England, Ireland, and 
the Channel Islands, rare in Scotland and northern England. 
British Records, Isle of Wight, Swanage, Weymouth, Sidmouth, Torbay, 
Plymouth, Looe (Batten, 1921), Falmouth, Penzance, Mount’s Bay, Trevone, 
Hilbre Island, Isles of Man and Anglesea, Arran, Cumbrae, Ballantrae, 
Portincross, Portrush, Bantry Bay, Miltown Malbay, Roundstone Bay, 
and the Channel Islands. 
Distribution in Europe. Atlantic and Mediterranean shores. 
LINN, JOURN, —BOTANY, VOL. XLVI, Z 
