154 DUDRESNAIA. 



the apical cells of these filaments cause the branches of the frond to appear 

 as if studded with red beads set in transparent glass. Fructification : 

 very dense, roundish masses of sporules, deeply seated among the radiant 

 fibres. In habit this remarkable plant a good deal resembles the grauuli- 

 ferous state of Gracilaria compressa, while the substance is more that of 

 Halymenia ligulata. 



XX. DODRESNAIA. Bonnem. [Plate 21, C.] 



Frond cylindrical, gelatinous, elastic ; the axis composed 

 of a lax network of anastomosing filaments, coated with a 

 stratum of closely combined, longitudinal fibres ; the peri- 

 phery of horizontal, dichotomous, moniliform filaments. 

 Fructification: 1, globular masses of spores attached to the 

 filaments of the periphery ; 2, external tetraspores, borne by 

 the filaments of the periphery, and generally terminating a 

 ramulus. Name, in honour of M. Dudresnay, a French na- 

 turalist. 



1. D. coccinea, Ag. ; frond fine rose-red, tender and gela- 

 tinous, much and irregularly branched ; branches alternate, 

 flexuous, moniliform, attenuated towards the apex ; ramuli 

 more or less numerous. Harv. Pliyc. Brit. t. ccxliv. Meso- 

 gloia coccinea, Hook. Br. Fl. ii. p. 386 ; Wyatt, Alg. Damn. 

 No. 148. Rivularia verticillata, E. Bot. t. 2466. 



Southern shores of England and Ireland, very rare. Summer. Brigh- 

 ton, Mr. Borrer. Bantry Bay, Miss Hutchins. Sidmouth and Torquay, 

 Mrs. Griffiths and Miss Cutler. Frond 4 8 inches high, of a fine rose- 

 red colour, very tender and gelatinous, from a quarter of a line to a line in 

 diameter at base, gradually attenuated upwards ; much and irregularly 

 branched, the smaller branches somewhat pinnated, moniliform, each series 

 becoming narrower. Under the microscope the branches appear composed 

 of numerous jointed, colourless, longitudinal fibres, set at close intervals 

 with dense tufts of rose-coloured, dichotomous filaments, which cause the 

 beaded appearance. The fruit is of two kinds, on distinct individuals : 

 1st, large dark red masses of minute spores (favellidia ) ; 2nd, elliptic-ob- 

 long or club-shaped tetraspores, with pellucid pericarps, borne abundantly 

 on the ramuli of the radiating filaments, generally terminating a ramulus. 



2. D. Hudsoni, Ag. ; fron.d much branched, filiform, pale 

 reddish ; branches mostly opposite, horizontal, once or twice 

 pinnate ; ramuli numerous, irregular, obtuse. Harv. Phyc. 

 Brit. t. ex. ; Hook. Br. Fl. ii. p. 386; Wyatt, Alg. Danm. 

 No. 99. Ulva rubens, Huds. Fl. Anal. p. 571. 



On stones and shells between tide-marks, not uncommon. Summer. 

 Frond excessively branched, slender, filiform, of a pale red or reddish 

 brown colour ; branches once or twice pinnated, with a lanceolate outline ; 

 ramuli abundant, 1 4 lines long, patent or divaricated, obtuse. The sub- 



