GRASS-GREEN SEAWEEDS 53 



In the green algae are found the extreme forms of one-celled 

 plants. In Pleurococcus the cell is microscopic in size. In the 

 Siphonese the plant still consists of a single cell, but it attains 

 large dimensions and develops into forms resembling, in outward 

 appearance, leaf, stem, and root (see Caulerpci). 



Other plants consist of single rows of cells, called filaments 

 (Confervaceae), or of cells arranged in layers or flat surfaces, called 

 membranes (Ulvaceae). 



ORDEE CONFERVACEJE 



The silkweeds. This order is characterized by cylindrical cells 

 strung end to end, forming threads or filaments, branched and 

 unbranched. The plants inhabit both fresh and salt water, and 

 are very abundant and widely distributed. They grow in dense 

 tufts, often matted at the base. 



GENUS Ulothrix 



A yellow-green, unbranched, decumbent, soft, hair-like fleece 

 on the surface of rocks, extending indefinitely. This genus dif- 

 fers from Gluvtomorpha in the character of its filaments, which 

 are soft and gelatinous in Ulothrix, but bristle-like and wiry in 

 Chcetomorpha. 



GENUS Chcetomorpha 



The frond is filiform; the filaments are coarse, rigid, and 

 unbranched. In some species the filaments grow straight and in 

 tufts from a definite base ; in others they are twisted together 

 and are prostrate.' Often they are found floating in masses. In 

 C. tortttosa the filaments are as fine as human hair, but rigid, and 

 so closely interwoven as to resemble a layer of wool on the rocks. 

 The cell-divisions give a striped appearance to the filaments when 

 dry. 



C. tnelagonium. This species is dark green, with filaments erect, 

 coarse as a double bristle, and wiry ; five to twelve inches long. It is 

 found in rock pools from Boston northward. It does not adhere to 

 paper in drying, and loses its color if immersed in fresh water. (Plate 



C7. cerea. Yellowish-green, with filaments erect and less rigid than 



