THE FRESH-WATER ALGAE 



161 



192 (193) Plant cylindrical, flattened, or branched, of a simple layer of cells, 

 reproduction by zoospores and isogametes. 



Enteromorpha Link. 



A 



193 (192) 



194 (i95) 



Frequently branched and variable in shape; chromatophore 

 parietal, with one pyrenoid. Zoospores with four cilia and a 

 pigment spot. Gametes with two cilia. 



Both zoospores and gametes are formed in the vegetative 

 cells except those at the base. 



The greater number of species of Enteromorpha are marine, 

 though E. intestinalis is found in the fresh water. Many of 

 the salt-water forms are very variable so that the species are 

 difficult to determine. 



FIG. 210. 



Enteromorpha intestinalis L. (Link), a. one-half natural 

 size. (After West.) b. X 360. (Original.) 



Plant in the adult stage a thin, membranaceous plate. . . . 194 



Chromatophore a thin, parietal lining to the membrane, with one 

 pyrenoid Monostroma Wittrock. 



The plant in early stages a hollow sack or cylinder, becoming 

 torn later, forming a membranaceous plate, near the base of 

 which certain cells elongate, grow downward and form strength- 

 ening supports. Reproduction by means of zoospores with four 

 cilia and smaller gametes with two cilia. These may germinate 

 without copulation. 



The membrane is at first very thin, but later becomes gelati- 

 nous so that the cells are more or less separated from each other. 

 Growth is not localized but is intercalary and the cells are often 

 clustered in groups of four. 



Monostroma bullosum occurs in shallow ditches, partially sub- 

 merged and partially swimming on the surface. 



FIG. 211. Monostroma bullosum Thuret. X 350. (After Reinke.) 



195 (194) Chloroplast star-shaped, radiating from the center, with one pyre- 



noid Prasiola Meneghini. 



Plant at first filamentous, but later a plate of cells grouped in 

 small areas. Rhizpids frequent at the base. Reproduction, ac- 

 cording to Lagerheim, in three ways: by isolated portions of the 

 plant, akinetes, and aplanospores. No zoospores known. 



Kiitzing has established a genus Schizogonium which greatly re- 

 sembles Prasiola. The chromatophore is stellate and the filaments 

 divide longitudinally to form two or more rows. The chief differ- 

 ence between this and Prasiola is that in the latter genus the 

 longitudinal divisions continue, while in the former they cease 

 after the first few times. 



Wille makes Schizogonium a subsection under Prasiola and is 

 followed in this by West. 



FIG. 212. Prasiola crispa Meneghini. X about 50. (After Oltmann 

 and Meneghini.) 



196 (191, 246) Plant filamentous 197 



197 (219) Filaments fine, mostly unbranched 198 



198 (217, 218) Filaments generally unbranched. Chromatophore a single, 



parietal curved plate or cylinder, rarely axial, or of several 



small, distinct discs, rarely more or less united into a network. 



Family ULOTHRICHACEAE . . 199 



