IV. FUCACE.E.— Cystoseiea. 65 



when full grown. It originates in a pinnatifid, midrlbbed, flat leaf, six or eight 

 inches in length, Avhose lowest laciniaj are short and deltoid ; the upper gradually- 

 longer, broadly linear, from three lines to half an inch in breadth, and from one to 

 three inches in length. As the plant grows older, the midrib of the first leaf 

 becomes slightly bordered with a thick lamina, and thus forming a two-edged stem, is 

 developed upwards ; and new lacinite, which are successively more compound as they 

 are more distant from the root, are formed along it. The lowest of these divided 

 lacinia^ are simply pinnatifid ; the next more deeply cut, and their lacinia3 changed 

 into vesicles. Those next in order are longer, more slender and more compound ; 

 and finally the upper branches of the fronds are slender and filiform, from one to 

 two feet in length, and twice or thrice pinnate. The air-vessels begin to be formed 

 on the first divided laciniae of the young plant, and are produced in great abundance 

 on all the upper branches, sometimes every ramulus, and ahvays several of those 

 nearest the base of the branch being changed into air-cells. On old plants, when 

 the upper liranches have reached their excessively divided condition, the apices of 

 the air-vessels frequently are extended into ramuli, which become again branched, 

 and even develop small air-vessels along their branches. The receptacles are of 

 small size, short, thickish, simple or forked, tuberculated, and spring from the tips 

 of the uppermost air-cells on fully developed plants. The colour when dry is a 

 dark rich brown, and the substance is thick and leathery. 



Turnei^'s figure is taken fi'om a young, undeveloped specimen. In our plate we 

 have shown the appearance of a young stem, and the base of an older one, which 

 would have extended nearly thrice as high as the portion admitted into the figure ; 

 the upper secondary branches becoming longer and more compound. Some of 

 these upper branches are indeed so much divided, that, apart from their bases, they 

 may be mistaken for parts of a Cystoseira, and have much resemblance to C. expansa, 

 but are more robust. 



IV. CYSTOSEIRA. Ag. 



Root a conical disc. Frond much divided, either in a pinnate or dichotomous 

 manner, the upper branches and ramuli filiform ; forming receptacles by transfor- 

 mations of the ultimate ramuli, and air-vessels by swellings of the branches or 

 ramuli. Branches alternate, naked or clothed with spine-like ramuli (or leaves). 

 Air-vessels usually several together, forming a moniliform chain in some part of 

 the branch. Receptacles formed by the transformation of the terminal ramuli, terete, 

 tuberculated, smooth or thorny, of a densely cellular substance ; having numerous 

 pores, beneath which are placed the spherical conceptacles (or spore-cavities). 

 Spore-cavities containing both spores and antheridia in the same loculus. Spores 

 numerous, oblong or obovoid, subsessile, having a hyaline perispore. Antheridia 

 on branching filaments, racemose. Paranemata simple, clothing the walls of the 

 conceptacle. 



VOL. ni. ART. 4. K 



