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ON A NEW BRITISH ALGA (VAUCHERIA SPHOE-
ROSPORA, NORDSTEDT) LATELY FOUND NEAR
MALDON.
By E. M. HOLMES, F.L.S., etc.
[Read November 28th, 1885.]
During a recent visit to this country Professor Otto Nordstedt
detected several species of Vaucheria new to Great Britain, and
amongst them a form of V. sphoerospora near Maldon, in Essex, growing
along the banks of the river for "one mile on both sides of the bridge."
This plant is an interesting one for several reasons, and a brief
notice of it may therefore possibly be acceptable to the members
of the Essex Field Club.
In a revision of the genus Vaucheria, published in the "Botaniska
Notiser" for 1879 (p. 177), Prof. Nordstedt divides the genus into
two principal sections, one of which has the antheridia sessile on
the filaments of the thallus, and in the other there is an intermediate
empty cell between the antheridium and the thalline filament. The
species under consideration belongs to the second section, and to a sub-
division of it, characterised by the oogonium, or female reproductive
organ, containing a globular oospore ; the oogonium being attached
directly to the thalline filament, i.e. without an intermediate cell.
To this sub-division belong the following species :— V. sphoerospora,
Nordst, and its variety dioica, Rosenvinge ; V. intermedia, Nordst.
and V. coronata, Nordst. The last is easily recognised by the
oogonium having five or six projecting openings, forming a sort of
crown at its apex, and by the cylindrical antheridium having an
obtuse apex, and only one, or rarely two, lateral openings. V. inter-
media has the oogonium nearly sessile, and furnished only with one
apical opening, and the antheridium has an obtuse apex with several
lateral openings, and either arises from the oogonium itself, or is
attached close to its base.
Vaucheria sphoerospora differs from the last in the oogonium being
pyriform, i.e. tapering below into a short cylindrical stalk, the
globular oosphere filling the upper portion only ; the antheridium is
cylindrical acute, with one opening at the apex, and two or more at
the sides.
In the typical form of the plant the antheridium arises from near
the base of the oogonium, and the two organs are therefore easily
observed at the same time. In the plant found by Dr. Nordstedt at