Monostroma areolatum Setch. & N.L.Gardner

240	University of California Publications in Botany [Vol. 8	univ. calif, publ. bot. vol. s	[ setchill-gardner i plate 25
4.	Monostroma areolatum S. and G.
Plate 25 and Plate 26, fig. 2
Frond very delicate, lubricous, 20-35 cm. high, sessile, saccate when
young, soon splitting and forming numerous, long, broadly ovate or
obovate, undulate, plicate and much crisped lobes, pale green ; mem-
brane distinctly and finely areolate, 9-12/x thick; cells with rounded
angles, 6-7/* diam., subspherical in cross section, grouped within each
areole.
Growing 011 Zostera in quiet waters. Sitka, Alaska.
Setchell and Gardner, Phyc. Cont. I, 1920, p. 281, pi. 30 and
pi. 31, fig'. 2.
This species of Monostroma is exceedingly beautiful and among the
most delicate and flaccid of the genus. The frond remains saccate for
a brief period only, attaining a height of but a millimeter or two.
The sack then breaks and the membrane spreads out at once, early
developing small lobes. Finally a few primary lobes are established
and these develop numerous secondary lobes. The growth 011 the
whole margin greatly exceeds that of the interior, which results in
the production of a great number of folds, making the margin very
much crisped. In the thickness of the frond and shape of the cells
M. areolatum closely approximates M. zostericola Tilden. The cells
of the latter are, however, more angular and more closely placed, and
the frond is not divided into areolae. There is a marked difference
in the size of these two species as well as in their method of develop-
ment. M. zostericola is diminutive, remains saccate for some time,
and then splits longitudinally, forming several lobes broadening out-
ward. M. areolatum very closely resembles the genus Prasiola in the
grouping of the cells as seen in surface view.
PLATE 25
Monostroma areolatum S. and G.
A photograph of a whole dried plant, the type. X 0.5.
Monostroma areolatum S. and G.
Fig. 2. A micro-photograph of a part of the surface.
Plates 21-26 are from Setchell and Gardner, Phyc. Cont. I, 1920, pp. 279-324.
pis. 26-31.
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NEW YORK BOTANICAL GARDEN
02133045