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THE MARINE ALGÆ OF NEW ENGLAND.
Fructification borne at the base of cortical filaments; plurilocular sporangia
cylindrical, composed of few cells in a row; unilocular sporangia globose.
Fronds forming small tufts on other algæ.
Cortex with a series of exserted colored filaments ......Elachistea.
Cortex destitute of exserted filaments .......................... Myriactis.
Fronds irregularly globose, hollow at maturity ..................Leathesia.
ELACHISTEA, Duby.
(From ελαχιστα [elachista], very small.)
Fronds olive-brown, tufted or pulvinate, basal portion solid, some-what
parenchymatous, composed of densely packed branching filaments, which become
free at the surface and branch corymbosely so as to form a layer of short filaments
(paraphyses), at the base of which are borne the sporangia of both kinds and a series
of long exserted filaments; hairs formed at the base of the paraphyses, exserted;
unilocular sporangia rhombic-ovoid, plurilocular sporangia cylindrical, composed of
a few cells in a linear series.
A genus consisting of a few species, all of which form small tufts on other algæ, especially on Fucaceæ.
They may be recognized by the double series of filaments borne on the surface of the solid and but
slightly developed basal portion. The longer filaments and hairs float freely in the water, but the
shorter paraphyses are packed rather closely together, forming as it were a definite cortical layer over
the basal portion. The unilocular sporangia are common. The more or less solid basal portion of the
fronds in some of the species gives off filaments which penetrate into the substance of the algæ on
which they are growing, and by the growth and persistence of these filaments it may be that the species
are propagated from year to year, as happens in the case of certain fungi. In other species no
penetrating basal filaments have as yet been found.
The limits of the species are pretty well defined except in the case of E. fucicola, E. lubrica, and E.
flaccida, where it must be confessed the species show a tendency to run into one another. In the present
case we have included in Elachistea only the species in which, besides the paraphyses which cover the
surface, there are long projecting colored filaments as in E. scutulata, on which Duby founded his genus
Elachistea in the Botanicon Gallicon. Here undoubtedly belong E. fucicola and its allies, but the same
can hardly be said of E. pulvinata, which was made by Kützing the type of his genus Myriactis. In this
species the surface of the frond is covered by the paraphyses, but there is not in addition a series of
elongated filaments as in E. fucicola, for the exserted hairs in E. pulvinata are of a quite different
nature. We have referred E. pulvinata to the genus Myriactis, not, however, limiting the genus as
Kützing has done, for some of the forms placed by him in Phycophila should be referred to Myriactis,
although the greater part of them are correctly placed by algologists in Elachistea. It may be that there
exist forms intermediate between the true Elachisteæ and Myriactis, but, from the study of dried
specimens, we have not been able to come to such a conclusion. It should be remarked that M.
pulvinata is placed in Elachistea by the most prominent algologists, as Thuret and Bornet, Agardh,
Harvey, Le Jolis, and others. The unilocular sporangia are most common in summer, and the
plurilocular sporangia are more frequent early in the season.