RALFSIA — ELACHISTKA. 49 



IV. Ralfsia. Berk. [Plate 10, D.] 



Frond coriaceo-crustaceous, fixed by its inferior surface, 

 orbicular, concentrically zoned ; composed of densely packed, 

 vertical, simple filaments. Fructification : depressed warts, 

 scattered over the upper surface, containing obovate spores 

 fixed to the bases of vertical filaments. — Name, in honour of 

 John Ral/s, Esq., of Penzance, the well-known author of a 

 monograph on British DesmidiecB and other works. 



1. ^. verrucosa, Xxe9>c\\.; frond orbicular, spreading; the 

 margin thin and closely adherent ; the disk densely covered 

 with irregular warts. R. deiista. Berk. ; Harv. Phyc. Brit, 

 t. xcviii. [not of Ag). Pndina deusta, Hook. Br. Fl. ii. 

 p. 281 ; Harv. Man. Ed. I, p. 31. 



On rocks between tide-marks, common. Perennial. Winter. — Fronds 

 forming lichen-like patches on the surface of flat rocks, from one to six 

 inches in diameter; when young orbicular, but becoming very irregular in 

 outline when old. In young specimens the surface is nearly flat and even ; 

 but in full-grown plants is exceedingly rough, with wart-like prominences. 

 Structure very dense and opaque. Fruit rare, and difficult to find. Colour 

 a dark brown. Substance leathery, hard. 



V. Elachistea. Fries. [Plate 10, F.] 



Frond parasitical, consisting of a dense tuft of free, simple, 

 articulated, olivaceous filaments, rising from a common tuber- 

 cular base, composed of vertical branching fibres closely com- 

 bined into a cartilaginous mass. Fructijication : pear-.shaped 

 spores attached to the bases of the filaments, concealed in 

 the tubercle, and frequently accompanied by paranemata. — 

 Name, sxaxftrra, the least ; from the small size of these plants. 



1. E. fucicola, Velley ; tufts pencilled ; filaments elongate, 

 flaccid, membranaceous, attenuated upwards ; articulations 

 once or twice as long as broad ; tubercle hemispherical. 

 Harv. Phyc. Brit. t. ccxl. Conferva fucicola, Hook. Br. 

 Fl.p. 354; Wyatt, Alg. Damn. No. 192; Dillw. Conf. t. 66. 



Parasitical on Funun vesiculosus, very common. Annual. Summer. — 

 Tufts an inch long, olivaceous or rusty brown, rising from a hemispherical 

 tubercle composed of dichotomously branching fibres. The filaments rise 

 from the terminal cells, and are surrounded at their origin by four or five 

 slender, club-shaped paranemata, among which the spores nestle, and 

 which, by their lateral cohesion, form the periphery of the tubercle. 



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