RED SEAWEEDS 87 
like little balls, either adherent to the branches, or raised on short 
stalks. It is the largest group, and contains many of the most 
beautiful of the red alge. 
Genus Polysiphonia 
(‘‘ Many tubes "’) 
A filament of Polysiphonia appears, when seen under the mi- 
croscope, like a bundle of filaments made up of a central tube, or 
axis, surrounded by a number of other tubes. It is by the number 
of these parts, called siphons, which vary in number from four 
to twenty, that the species is determined. In some plants the 
siphons are surrounded by a layer of cells, called corticating or 
bark cells, which give the filaments a solid, uniform appearance. 
In others the siphons are naked, and the filaments then seem 
striped or banded with color. It is difficult, without a micro- 
scope, to be sure of the classification. There are, however, other 
characteristics which separate many of the species, and some of 
these are described below. Two hundred species of Polysiphonia 
have been named by algologists. The plants are plentiful on all 
shores, especially in warm, shallow waters. Some species are per- 
ennial, but most of them are annuals and disappear in winter. 
P. fastigiata. This species grows on Ascophyllum nodosum in a 
globular tuft, and appears like a dark-brown ball, one inch to three 
inches in diameter. The frond isa dense mass of rigid filaments branch- 
ing many times in a forking manner and at broad angles. The ends are 
of nearly equal length, giving the plant a spherical shape. It is common 
from New northward at all seasons, and is easily recognized by its 
general form and place of growth. Egg-shaped cystocarps, or spore- 
yoccur in the ends of the terminal filaments. (Plate XXV.) 
. nigrescens. Frond three to twelve inches long, rigid below, soft 
above; main stem thick as a bristle, but not always easy to distinguish ; 
branches alternate and densely branched at the ends; siphons twelve to 
sixteen in number; filaments banded; color black or very dark brown. 
(Plate X XVII.) 
P. parasitica. Frond one inch to three inches long; branched in a 
pinnate or feather-like manner ; filaments flat ; all branches and branchlets 
emanating from the edges and on the same plane, giving a flat frond; 
color reddish-brown; resembles a fine Ptilota plumosa; cystocarps on 
short stalks. It is found on the California coast. (Plate XXV.) 
P. dendroidea. This is a variety of the species P. parasitica. Frond 
four to five inches long; main branches placed at irregular intervals, 
but the secondary branches at regular intervals and alternate; branches 
