IV. 
FUCACEiE. — Cystoseira. 
65 
when full grown. It originates in a pinnatifid, midribbed, flat leaf, six or eight 
inches in length, whose lowest laciniaa 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 laciniae, which are successively more compound as they 
are more distant from the root, are formed along it. The lowest of these divided 
laciniae are simply pinnatifid ; the next more deeply cut, and their laciniaa 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 always several of those 
nearest the base of the branch being changed into air-cells. On old plants, when 
the upper branches 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. 
Turner’s figure is taken from 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. 
IY. CYSTOSEIRA. Ay. 
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. III. art. 4. 
K 
