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THE MARINE ALGÆ OF NEW ENGLAND.
0076 mm broad by about .057 mm long, composed of 8-10 cells in a row unilocular
sporangia.
Parasitic in the cryptostomata of Sargassum vulgare. Summer.
Wood’s Holl, Mass.
This species forms minute tufts on Sargassum, and is so small as easily to escape detection. It is
furthermore likely to be mistaken for the hairs normally found at certain seasons in the cryptostomata.
The description given above applies to the plant found at Wood’s Holl, which is smaller than the typical
M. pulvinata of Europe, which grows in the cryptostomata of various Cystoseiræ. In the European
specimens examined the paraphyses were decidedly stouter, rarely being less than .018 mm in breadth,
whereas with us they are seldom more than .010-12 mm broad. Our plant is through- [sic] but smaller
than the European, but, in proportion, the paraphyses are longer and slenderer. It remains to be seen
whether we are correct in considering our form a mere variety, or whether it should be kept distinct.
Perhaps it may be the Phycophila arabica of Kützing, Tab. Phyc., Vol. 8, Pl. 1, Fig. 2, which grows on
Cystoseira myrica. The species is not uncommon in summer at Wood’s Holl, and both forms of sporangia
occur together, the unilocular being much less abundant than the plurilocular.
LEATHESIA, S. F. Gray.
(Named in honor of Rev. G. R. Leathes, a British naturalist.)
Fronds olive-brown, gelatino-carnose, forming irregularly globose masses, solid
when young, but soon becoming hollow; internal portion composed of radiating,
dichotomous filaments, formed of large, irregular, colorless cells, the terminal ones
bearing a series of short, simple, colored filaments (paraphyses), which are densely
packed together, constituting the cortical layer of the frond; sporangia and hairs
borne at the base of the paraphyses; plurilocular sporangia cylindrical, composed of
few cells in a single row; unilocular sporangia pyriform or ovoid.
A small genus, comprising not more than half a dozen species, of which L. difformis is common in the
North Atlantic. Leathesia Berkeleyi, Harv., now placed in the genus Petrospongium,; Næg., although
found not rarely in Europe and apparently tolerably common on the coast of California, has not yet
been detected in New England, but may be expected. It forms rather leathery expansions on rocks at
low-water mark.
L. DIFFORMIS, (Linn.) Aresch. (Tremella difformis, Linn., Syst.—Rivularia
tuberiformis, Engl. Bot., Pl. 1956.—Corynephora marina, Ag., Syst.—Leathesia
tuberiformis, Gray, in Phyc. Brit., Pl. 324, and Ner. Am. Bor., Vol. I, Pl. 10 c; Thuret,
in Ann. des Sciences, Ser. 3, Vol. XIV, Pl. 26, Figs. 5-12.) (Pl. V, Fig. 1.)
Fronds from half an inch to two inches in diameter, solitary or aggregated, at first
globose and solid, becoming irregularly lobed and hollow; plurilocular sporangia
produced early in the season, unilocular sporangia in summer.