Mesotaenium aplanosporum Taft

Separately printed, without change of paging from Bulletin of the Torrey
Botanical Club 64: 75-79. February, 1937.

The life history of a new species of Mesotaenium1

Clarence E. Taft

Mesotaenium aplanosporum sp. nov.

Cellulis oblongis, cylindracis, apicis orbiculatibus, in orbem flexus; longi-
tudinibus 1|-2| frequenter marjorim diametrim, curvatis levitis; coloro
corporo auxio orbox. Cellulis in gelatis matricis inditis.

Zygosporis globosis vel ovatis; globosis abnormis saepe, extero muro
papillatio densiter et abnormiter; rubeis fuscis coloribus.

Aplanosporis isdem formis quam vegetativis cellulis, papillatis; papillis
postulatis in transversis ordinibus circimque semenibus, rubeis fuscis coloribus.

Cellulis vegetativis 13-17¡j. latis, 18-35/¿ longioribus; Zygosporis 20-23 ¡jl
latis, 20-27/z longioribus; aplanosporis 11-14/z latis, 28-34/z longioribus.

Cells oblong-cylindrical, apices rounded, length 1^-2^ times the diameter,
slightly curved; chloroplast an axial plate. Cells embedded in a gelatinous
matrix.

Zygospore globose to ovoid-globose, often irregular, outer wall densely
and irregularly papillate, red-brown in color.

Aplanospores the same shape as the vegetative cell, papillate; papillae
arranged in transverse rows about the spore. Color red-brown.

Veg. cell 13-17/^X 18-35yu; zygospore 20-23^X20-27^; aplanospore ll-14¿i
X28-34yu.

This species is to be compared with Mesotaenium chlamydosporum
forma minor W. & G. S. West. In the vegetative condition it will doubtless
be difficult to distinguish the one from the other although the diameter
of the vegetative cells of West’s forma minor is somewhat less than that
of aplanosporum. In their monograph (the British Desmidieae, West, W. &
West, G. S. 1904) the Wests give 10/jl as the maximum width for their form
while the minimum width observed in aplanosporum was 13/jl. Therefore
the chief diagnostic character is the ornamentation of the zygospore wall.

The outer spore wall of forma minor according to West is involúcrate
while in aplanosporum it is densely and irregularly papillate. Otherwise
the zygospores are comparable.

During July of 1932 a collection of algae was taken from a dripping
sandstone cliff of the Blackhand Conglomerate Formation in Jackson
County, Ohio. The summer had been exceedingly hot and dry, but due to
seepage springs and a northern exposure, the face of the cliff remained
covered with a thick gelatinous layer of microscopic organisms. A number
of samples were taken with the supposition that they might contain some
members of the genus Mesotaenium or Cylindrocystis. This material upon
examination proved to be almost a pure culture of a single species of

1	Paper from the Department of Botany, Ohio State University, No. 381.

01192665

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