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(i.")4 University of California Publications in Botany [Vol.8
]>. 73) and related to D. pinnatifida Kuetzing (Tab. Phyc, vol. 9, 1859,
p. 16, pi. 39, fig. 1), to D. Pappeana Kuetzing {Joe, cit., pi. 38, fig. 2),
and to D. liturata Kuetzing {lac. cit., fig. 1). The cross-section in
the central and lower parts of the frond has a structure similar to
that shown by Okamura (1913, p. 33, pi. 109, figs. 3, 7) for D.
)Har(jinata, In D. Johnstonii the margins are thickened by divisions
of the cells of both the medulla and the surface, while in D. marginata
increase in thickness is brought about by division of the medullary
cells only.
4. Dictyota Vivesii Howe
Fronds densely caespitose, stupose at the base, 7-9 cm. high, 135-
160/A thick (240/x, at the base), collapsed and thin on drying, somewhat
regularly 3-6 times dichotomous below, the branches then rather
closely 3 or 4 times subflabellately or subpinnately dichotomous,
sinuses mostly rather acute, margins entire or slightly undulate ; main
segments oblong or obcuneate, 3-8 mm. broad, diminishing in length
and width upward, terminal segments 1-2 mm. wide; cortical cells
nearly uniform in size, 19-65/* long, 11-27/x wide, interior cells much
larger and very thin-walled ; aplanospores forming small, scattered,
inconspicuous sori.
Collected by Senor G. V. Vives at La Paz, Lower California, in
February, 1911.
Howe, Phyc. Stud. V, 1911, p. 497, pi. 27.
Dictyota Vivesii seems to be a near relative to D. Bartayresiana
Lamour. from the West Indies. According to Howe (1911, p. 498) :
' It is more caespitose in habit of growth than D. Bartayresiana, more
stupose at the base, less regularly dichotomous towards the apices,
rather broader in its broadest parts and more conspicuously dwindling
in width as the ultimate segments are approached, the axils (the
upper at least) are more acute and the segments less patent or divari-
cate, the apices are less acute, and both the cortical and the interior
cells are for the most part narrower and the cortical cells overlaying
the septa and lumina of the interior cells show scarcely any of that
differentiation in form and translucency that led J. Agardh to
describe B. Bartayresiana as 'fenestrate.' "