Percursaria percursa (C.Agardh) Rosenv.

Percursaria percursa (Ag.) Rosenv.
Plate 14, fig. 6
Frond several era. long, flexuous and contorted, generally irregu-
larly and frequently contracted to a single row of cells or expanded
to a double row; cells 10-15/j. wide and from once to twice as long.
In entangled masses with other filamentous algae in upper tide
pools, in ditches in salt marshes and similar places w'here the water
is warmed by the sun. From Alaska (Bay of Unalaska) to central
California (San Francisco Bay).
Rosenvinge, Groenl. Ilavalg., 1893, p. 963, Alg. Mar. du Groenl.,
1894, p. 160. Conferva percursa Agardh, Syn. Alg. Scand., 1817,
p. 87. T etranema per cur sum Areschoug, Phyc. Scand. Mar., Sect. II,
1850, p. 418. Diplonema, percursum Kjellman, Norra Ishafv. Algfl.,
1883a, p. 371, Alg. Arct. Sea, 1883, p. 302. Entero-morpha percursa
Setchell and Gardner, Alg. N.W. Amer., 1903, p. 214; Collins, Green
Alg. N. A., 1909, p. 197; Collins, Holden and Setchell, Phyc. Bor.-
Amer. (Exsicc.), no. 968.
This interesting plant, so unlike a member of the Ulvaceae in
general appearance, seldom occurs pure, but is generally mixed with
those species of Claclophora, Enteromorpha and filamentous Myxo-
phyceae which delight in the same conditions of life. It is readily to
be told from its associates by the very symmetrically placed double
row of cells.
Percursaria percu.sa (Ag.) Rosenv.
Fig. 6. A portion of a frond showing one row of cells at one end and two
rows at the other. X 250.
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