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114
THE MARINE ALGÆ OF NEW ENGLAND.
or immersed in the frond; antherozoids formed from the cells of the protuberances or
the superficial cells of the frond; cystocarps composed of few spores arranged end to
end in a few rows, or in filaments which branch slightly; tetraspores zonate or
cruciate, stalked or attached laterally to the filaments of the frond or protuberances.
A small order, more abundant in tropical seas than on our coast, comprising species which in habit
resemble lichens rather than algæ. A few species, as Peyssonnelia squamaria and P. australis, attain a
considerable size, and are distinctly foliaceous. The greater part of the species, however, form closely
adherent crusts, which are sometimes more or less gelatinous and sometimes slightly calcareous. The
structure of the fronds is simple. From a horizontal base, composed of a single layer or a few layers of
cells, arise vertical filaments, which in some genera are densely united so as to form a parenchymatous
frond, or in others are only slightly held together by a gelatinous intercellular substance. The
fructification is found either in external raised spots or sunk in the frond. The antheridia are either
formed directly from the cells of the filaments which constitute the protuberances or from the external
cells of the fronds themselves. The tetraspores are either cruciate or zonate, and their position
constitutes an important generic mark. The development of the systocarps is known in only a few
species. In Peyssonnelia, according to Dr. Bornet, the procarp is formed from the cells of the filaments,
which form the protuberances. The upper cell elongates and forms the trichogyne, and the fertilization
consists merely in the change of the cells of the procarp into spores, thus constituting a very simple
form of cystocarp, to which Zanardini has given the name of cystidie. According to Prof. Fr. Schmitz, in
Cruoriopsis cruciata, Dufour, there are winding filaments like those described by Thuret and Bornet in
Dudresnaya. We have but few Squamarieæ on our coast, and the study of the suborder cannot easily be
pursued with us.
PEYSSONNELIA, Decaisne.
(Named in honor of J. A. Peyssonnel.)
Fronds horizontally expanded, attached by the under surface; substance
parenchymatous throughout; fructification in external convex protuberances
(nemathecia) composed of slender parallel filaments, on which are borne the
antheridia, cystocarps, and tetraspores; antherozoids produced in all the cells of the
nemathecial filaments; tetraspores cruciate, oblong, sessile or shortly stalked;
cystocarps composed of few spores, placed one over another in one or two rows or in
short, branching filaments.
A small genus, comprising probably not more than twelve or fifteen good species. P. squamaria,
common in Southern Europe, is not known with us. It may be that several of the species described by
Crouan in the Annales des Sciences and the Florule du Finistère occur with us; but it must be
confessed that from the description given by Crouan it would be by no means an easy matter to
recognize them. Those who have an opportunity for dredging on shelly bottoms at localities like Gay
Head, Block Island, Montauk, or Eastport should make a careful search for species of the present
genus.