306 DR. LILY BATTEN ON 
4. P. NIGRESCENS Grey. in Smith's Engl. Flora, v. 1833, p. 332. 
Conferva nigrescens Dillw. Brit. Conf. 1809, pl. 155. 
P. violascens Kütz. Spec. Alg. 1849, p. 813. 
P. regularis Kütz. Tab. Phyc. xiii. 1863, p. 16, tab. 51 (a, b). 
P. sentosa Kütz. Tab. Phye. xiii. 1863, p. 16, tab. 51 (e, d). 
P. lophura Kütz. Tab. Phye. xiii. 1863, p. 17, tab. 52 (e, d). 
References. Agardh (2) ii. p. 1057; De Toni (22) iv. p. 940; Falken- 
berg (24) p. 129 ; Hauck (31) p. 244. 
Icones. Dillwyn, Brit. Conf. 1809, pl. 155. Harvey, Phyc. Brit. 1846- 
51, pl 277. syn. 122. Kützing, Tab. Phye. l.c. pls. 51, 52 (e, d), 
56 (f-i). | Ewsiccata. Wyatt, Alg. Damnon. no. 135. 
DESCRIPTION.— Habit, A perennial, occurring in tufts as much as 5 cms. 
in diameter, and varying from a slender plant about 7 cms. in length to a 
coarse form attaining a length of 30cms. and having the lower parts clad 
with the broken remains of old ramuli. Branching variable but typically 
alternate, the branches subdividing and ultimately bearing large numbers of 
elosely pinnate ramuli, which are themselves again doubly-pinnate and bear 
dichotomous fibrillæ at their tips. During the winter the ramuli disappear, 
leaving the plant with a serrate appearance. The substance is rigid except 
in the ramuli, which are flaccid and adhere to paper. Siphons. 12-20 peri- 
central, round a central one with diameter equal to about one-third of the 
diameter of the filament. At the extreme basea row of small cells frequently 
bounds the pericentral siphons on the outside. Colour. Brownish-purple. 
Anatomy. Articulations about as long as broad in the older parts, but attain- 
ing a length of 14 times their breadth in the smaller branches. Attachment 
organ. At the base of the main axis a number of rhizoids occur, formed from 
the longitudinal elongation of pericentral siphons. Later, when cortication 
develops, external cells aid in the formation of the attachment organ, and 
procumbent branches send off rhizoids from their creeping portions. The 
dises at the apices of the rhizoids are well developed, affording additional 
resistance to the force of the waves by their mechanical interlocking, the 
part actually coming in contact with the substratum being comparable to the 
base of the attachment in complex forms like P. elongata. Reproductive 
organs. Tetraspores borne in the ramuli and uppermost branches, frequently 
intercalary in development. Antheridia formed in yellow clusters at the tips 
of the ramuli, usually among clusters of multicellular hairs. Cystocarps 
broadly egg-shaped and almost sessile. 
This species often bears a strong outward resemblance to Pterosiphonia 
thuyoides Sch., although the branching is not so regular. It may be distin- 
guished with a hand-lens by means of the attachment organ, the tiny 
branches specially modified for attachment which are present in Pterosiphonia 
thuyoides being absent in P. nigrescens, 
