The Plant World 



A MONTHLY JOURNAL OF POPULAR BOTANY. 



Vol. 111. APRIL, 1900. No. 4. 



SOME ALGAE IN ORNAMENTAL WATERS. 

 By Mary G. Fanning. 



IN seeking algal material for study in high school classes it is not 

 necessary to go farther than the artificial ponds and lakes so common 

 in city parks. One such small lake, situated between Minne- 

 apolis and St. Paul, has been observed during the past autumn and 

 was found to contain many interesting forms. The lake, which covers 

 nearly an acre, has during the summer a small fountain in the center 

 which is fed by the city water. 



Among the blue-green forms found in the lake, Nostoc, Tolypothrix 

 and Gloiotrichia were the most abundant. 



The Nostoc colonies, (see fig. 1) each enclosing many hundreds of 

 filaments, are brownish-green, globular, jelly-like masses floating in 

 the water. A filament resembles a string of beads of two sizes, the 

 larger and less numerous known as hetei'ocysts, the smaller and more 

 numerous as cells. The^ filament grows in length by the division of 

 the cells. The plant or filament reproduces by the formation of spores 

 from these cells. Portions of these filaments, called horuwgones^ may 

 become detached, work out through the enclosing jelly, and surround- 

 ing themselves again with jelly, form a new colony. 



Tolypothrix (figs. 2, 3,) also forms colonies; that is, great numbers 

 of filaments, each one a single plant, occur in little masses or mats 

 floating in the water. The filament appears to be branched, but it is 

 false branching that takes place. The heterocysts, formed at varying 

 intervals, are fastened to the gelatinous sheath enclosing the filament. 

 As the filament, by growth and cell-division, increases in length, this 

 tension bursts the sheath and the filament protrudes throvigh the rent 

 like a bent bow. The bow finally breaks near one end and then the 



