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covered at an early age witli a vesicular membrane formed by a blistering
of tbe cuticle, fixed by tlieir bases, obovate, with a wide limbus, and
finally parted into four sporules. 2 . (on distinct plants) sohtary, roundish
spores (?) scattered among the cells of the surface.— ^Var. S- is very much
narrower, about a line in diameter at the base, and not a fourth of a line
above, dark broivn, coarser in substance, with more patent axUs, and
frequently spirally twisted.
A very common plant, the most widely dispersed of the genus
to which it belongs, being found along the shores of the greater
part of the temperate ocean, and also in many intertropical
localities. As might be expected, it varies considerably according
to the circumstances under which it grows, though without any
respect to climate, the most opposite varieties being frequently
found on the same shore. The variations appear to result merely
from the depth of water at which the plant grows, and the degree
of exposure to waves and currents to which it is subjected. In
rock-pools near high-water mark and to half-tide level the narrow
variety, which sometimes is much narrower and greatly more
intricate than our figure represents, is the commoner. Near
low-water mark in rock-pools, and among the Laminarioe in
sheltered bays, the broad variety occurs, of which the average
size is represented in the figure ; but some specimens in my
Herbarium, gathered by Miss Hincks, at BaUycastle, on the
coast of Antrim, are very much wider and proportionably less
compound, and bear a considerable resemblance to the tropical
L). Schroderi.
The narrow variety, especiaUy when spiraUy twisted as it
commonly is, looks very like a different species, and is regarded
by several continental authors as such. But it is merely distinct
in its extreme forms. Intermediate specimens connect it absolutely
with the broader individuals, and differences in relative
breadth are the most uncertain of aU characters, especiaUy among
the leafy marine plants. The diameter of cylindrical kinds is
more constant.
Fig. 1. Diotyota dichotoma, var. a. 2 . The same, var S — both ,
m l uze. 3. Portion of the frond with a vertical view of a sorus. ^ 4 A vertical
section of a sorus 5. A spore. 6 . Portion of the frond, with scattered
spores :— all i l l