Acrochaetium polysporum M.Howe

THE NEW YORK BOTANICAL GARDEN

MARINE ALGAE OF PERU, COLLECTED BY ROBERT E. COKER

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TYPE

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Acrochaetium polysporum sp. nov.

Basal disc well developed, monostromatic, suborbicular, mostly
!5ř~850m in diameter, closely adherent to the substratum, at
first parenchymatous, later often irregularly filamentous at the
margin, nearly all of the cells finally producing erect filaments;
cells of the disc 5.5-8.0 ¨1 broad, 1-2 times as long; erect filaments
very numerous, finally 300-500 fx (20-40 cells) long, with few or
many of the intermingled and marginal remaining 25-80 /x (2-6
cells) long, all simple or in very rare cases, with a single vegetative
branch, the cells cylindric or slightly tumid, 11-22 ju X 8-11 /*,
1-3 times as long as wide; chromatophore parietal, usually more
or less 2-lobed proximally and distally, often (especially before
cell division) so deeply lobed as to appear H-shaped, or merely
unilaterally cleft or irregularly and sparingly cribose, pyrenoid
usually a little eccentric; sporangia ovoid, 16-24/u X 8.5-12 ju,
polysporous, containing usually 8-16 (-32?) spores, lateral or
terminal, mostly in a secund lateral series of 3-20, very rarely-
opposite, sessile or with a unicellular pedicel, nearly every cell of
the erect filament sometimes giving rise to a sporangium, com-
monly also terminal on the short and less commonly on the longer
filaments, cells of the main filaments occasionally converted di-
rectly into sporangia and then becoming more or less unilaterally
gibbous or protuberant, the lateral and terminal sporangia often
regenerated from below. [Plate 31, figures i-ii.]

Growing on the laminae of Lessonia nigrescens, Pescadores
Islands, region of Ancon, Feb. 12, 1907, Coker 09150 p.p. (type);;
Chincha Islands, Coker 197 p.p.] also, rather poorly developed, on
the leaves of Macrocystis integrifolia, Chincha Islands, Coker 00614

Tw?y

Acrochaetium

89

p.p. So far as we are aware, polysporic sporangia have not hereto-
fore been attributed to Acrochaetium or Chantransia and their
manifest existence in the present species (the material is preserved
with formalin) might be considered by some to be sufficient ground
for making it the type of a new and separate genus, but so long as
monosporangia and tetrasporangia are not considered incongruous
in a single generic group (Acrochaetium or Chantransia), there seems
to be no compelling reason for refusing to admit polysporangia; in its
other characters, so far as the material at hand affords grounds for
judging, the plant is clearly a member of the group which includes
Chantransia virgatula secundata (Lyngb.) Rosenv., Chantransia
Macula Rosenv., and Acrochaetium flexuosum Vickers, even though
amply distinct from any of these. The polyspores are, as a rule,
discharged in a single mass and often adhere more or less and the
young thalli are commonly multicellular from the first. Occa-
sional cells of the older discs occur empty and we have found some
grounds for suspecting that cells of the prpstrate discs may here
and there be converted into sporangia, but the evidence on this
point is not conclusive. The erect filaments are nearly always
simple, except for the often pedicelled lateral sporangia. In
only three or four cases out of hundreds examined have we dis-
covered a vegetative branch and in no case more than one such.

Plate 31, figures i-ii. Acrochaetium polysporum.

1.	A portion of a typical basal disc.

2.	A portion of the margin of another basal disc.

3.	A portion of a more irregularly filamentous margin, showing chromatophores, etc,

4.	A typical erect filament, with secund sporangia, some sessile and others with a

one-celled pedicel. The lower emptied sporangia are being refilled from below.

5.	Another erect filament, showing a single elongate branch (of very rare occurrence)

terminated by a young sporangium. The main axis, also, is terminated by a