108 DICTYOTACE^.— DicTYOTA. iv. 



V. DICTYOTA. Lamour. 



Root coated with "woolly hairs. Frond flat, ribless, membranaceous, dichotomous 

 or sub-pinnatifid, reticulated ; the surface cellules minute, equidistant, converging 

 at the ends of the lacinise and ending in a single cellule. Concentric lines none. 

 Fructification ; roundish, scattered sori, bursting through the cuticle of both 

 surfaces of the frond, consisting at maturity of numerous obovate, tufted spores^ 

 with hyaline perispores. Paranemata in sori distinct from those containing spores, 

 clavate, articulate, filled with grumous matter. 



This genus, as recently reformed by Prof. J. Agardh, is easily known from any 

 of the preceding by the mode of development of the frond, each of whose lacini* is 

 seen to terminate in a single cellule, by the constant division of which at its lower 

 side the other cells of the frond are formed, the terminal cell being thus continually 

 pushed onwards. From this mode of growth it results that the longitudinal lines 

 of superficial cells, which in the flabellate genera already described diverge from 

 one another, in this converge: thus affording a ready method of ascertaining the 

 genus in default of fructification. 



1. DiCTTOTA Fasciola, Lamour. (?) ; fronds densely tufted, very narrow, mem- 

 branaceous, linear, many times dichotomous ; axils obtuse ; lacinise patent, very 

 entire ; apices acute ; sori forming a medial line, and often accompanied by filiform 

 processes. /. Ag. Sp. Alg. 1, p. 89. Kiltz. Sp. Alg. p. 555. Roth. Cat. Bot. vol. 

 1, p. 7, /. 1. Esp. Fug. t. 44. (?). (Tab. VIII. B.) 



Hab. On rocks and stones, and corals near low-water mark. Annual. Abun- 

 dant on the Florida Keys. Key West, Feb., W. H. H. (v. v.) 



Fronds forming large and dense tufts, matted together at the base, six to ten 

 inches in length, scarcely a line in breadth, of nearly equal breadth from the base 

 to the apex, many times dichotomous. The axils are conspicuously rounded and 

 the lacinia3 thus diverge one from another, particularly the upper ones. Some- 

 times the forking proceeds with equal arms throughout the tuft, and then the 

 plant forms round, fastigiate masses, the individual fronds not having any leading 

 stem. In other specimens one arm of the fork, at alternate sides of the growing- 

 branch, is constantly shorter than the other ; thus a frond Avith leading stems, 

 bordered with short, simple or forked laciniaj, is formed. The substance of the 

 frond is membranaceous, thickish and subopaque below ; the surface cells are about 

 four times as long as broad ; and the largish, hexagonal cells of the interior of 

 the frond may be seen through the exterior cells in the younger parts at least. 

 The apices are more or less acute, but not acuminate. The sori are disposed in a 

 line through the centre of the lamina. Those formed of paranemata are most 



