108 
DICT Y OT AC EiE. — Dictyota. 
iy. 
Y. DICTYOTA. Lamour. 
Root coated with woolly hairs. Froncl flat, ribless, membranaceous, dichotomous 
or sub-pinnatifid, reticulated ; the surface cellules minute, equidistant, converging 
at the ends of the laciniae and ending in a single cellule. Concentric lines none. 
Fructification ; roundish, scattered -son, 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 laciniae 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 afiording a ready method of ascertaining the 
genus in default of fructification. 
1. Dictyota Fasciola , Lamour. (?) ; fronds densely tufted, very narrow, mem- 
branaceous, linear, many times dichotomous ; axils obtuse ; laciniae patent, very 
entire ; apices acute ; sori forming a medial line, and often accompanied by filiform 
processes. J. Ag. Sp. Alg. 1 , p. 89- Kiitz. Sp. Alg. p. 555. Roth. Cat. Rot. vol. 
1, p. 7, /. 1. Fsp. Fuc. t. 44. (?). (Tab. YIII. B.) 
TIab. On rocks and stones, and corals near low-water mark. Annual. Abun- 
dant on the Florida Keys. Key West, Feb., IF. 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 laciniae 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 with leading stems, 
bordered with short, simple or forked laciniae, 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 
