104 DICTYOTACEJj:.— Padina. IV. 



other Algce ; for its form and substance are strikingly peculiar. Its fan-like shape, 

 and its property of reflecting prismatic colours whilst growing under water, have 

 won it the popular name of Peacock' s-taiL 



1. Padesta Pavonia, Lamour. ; frond between membranaceous and coriaceous, 

 broadly fan-shaped, entire or deeply and variously cleft, each lacinia being then 

 fan-shaped, powdery on its outer surface ; concentric lines numerous. Harv. Phyc. 

 Brit. t. 91. J- -Ag- Sp. Alg. 1, p. 113. Zonaria Pavonia., Kiltz. Phyc. Gen. t. 22. 

 /I. Sj}. Alg. p. 565. Ulva Pavonia, Linn. E. Bot. t. 1276. (Tab. VII. B.) 



Hab. On stones, &c. about low-water mark. Annual. Spring and eai-ly summer. 

 Abundant on some of the Keys at Florida, as at Sand Key in February, W. IT. H. 

 Later in the season it appears at Key West, Dr. Blodgett, &c. Conch Key, Prof. M, 

 Tuomey. (v. v.) 



Root densely coated and cushioned with woolly hairs. Fronds tufted, from two 

 to five or six inches in height, cuneate at the base, rapidly expanding into a broadly 

 fan-shaped lamina, whose upper margin forms constantly a circular arc. This 

 lamina, which is at first simple, is at length, as the plant advances in growth, 

 cloven into numerous lobes, by splits arising in some point of the margin and 

 proceeding downward toward the base : each lobe, at first cuneate, soon becomes, 

 by the rapid lateral development of its arched margin, fan-shaped like the primary 

 frond. The whole fronds of young plants, and the several laciniae of older, are, 

 when the plant is growing, rolled up in little conical or funnel-shaped cups. At 

 distances of one or two lines, the frond is marked with concentric bands, more or 

 less evident, according to age, along each of which is developed a fringe of 

 extremely slender, orange coloured, jointed hairs. These hairs, which in young 

 plants are found on every band, are limited on older specimens to the last formed 

 bands, and at length disappear. The margin at the summit of the frond is always 

 strongly rolled inwards ; the outer or lower surface of the lamina is whitened with a 

 variable quantity of chalky powder ; the inner surface, except for the fringes of hairs, 

 is smooth, olive-coloured, greenish towards the summit. The sori of fructification 

 form concentric bands, alternating between the fringed bands. They are at first 

 concealed beneath the surface-cells, but burst through in lines, raising the membra- 

 nous skin of the frond, which then folds over them like the indusium of a fern. 

 At maturity, the sorus consists of numerous obovate, hyaline perispores, fixed to a 

 linear receptacle, each containing four sporules. Paranemata, club-shaped, articu- 

 lated filaments, are found also in concentric bands, parallel to those which produce 

 spores, and placed at short distances from them. 



Plate VII. B. Fig. 1 . Plant of Padina Pavonia ; the natural size ; jig. 2, part 

 of the surface, showing portions of the band-like sori of spores^ and of paranemata 

 respectively ; fig. 3, vertical section of the frond, showing spores in situ ; fig. 4, 



