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 algse. 



GENUS Polysiphonia 



C" Many tubes ") 



A filament of Polyaiphouia 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. fastlgiata. 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 is a 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 York northward at all seasons, and is easily recognized by its 

 general form and place of growth. Egg-shaped cystocarps, or spore- 

 cases, occur in the ends of the terminal filaments. (Plate XXV.) 



P. nigrescent. 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 XXVII.) 



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. deiidroidea. This is a variety of the species P. parasitica. Frond 

 four to five inches long ; main branches placed at irregular intervals, 

 out the secondary branches at regular intervals and alternate j branches 



