114 



FRESH-WATER BIOLOGY 



69 (70) Filaments radiately disposed in a globose or hemispherical, at- 

 tached mass. Spores unknown Rivularia Agardh. 



Forming hemispherical, globular, or hollow 

 spherical colonies attached to submerged 

 plants, such as Chara, Myriophyllum, or to 

 stones in streams and cataracts. Colonies 

 composed of radiating filaments which are 

 repeatedly branched; filaments attenuated 

 and with piliferous extremities; heterocysts 

 basal; the whole enclosed in a tough, gelat- 

 inous matrix. 



Fig. 67. 



Rivularia minutula Bornet and Flahault. 

 X 300- (After West.) 



70 (69) Filaments radiately disposed; colony often free-floating. Spores 

 regularly present Gloeotrichia J. Agardh. 



(Probably not sufficiently 

 distinguished from Rivularia to 

 justify its being made a sep- 

 arate genus.) Colony globose, 

 free-floating or attached to 

 submerged water plants; soUd 

 when young, but inflated and 

 hollow when old; composed of radiating, branched, attenuated filaments. 

 Spores elongated, cylindrical, borne immediately above the basal heterocyst. 

 G. pisum Ag. is a common plankton form and constituent of "water- 

 bloom." 



Fig. 68. Gloeotrichia pisum Agardh. X 465- (Original.) 



IMPORTANT REFERENCES ON BLUE-GREEN .\LGAE 



Farlow, W. G. 1877. Remarks on some algae found in the water supplies 



of the City of Boston. Bull. Bussey Inst., 2: 75-80. 

 Forti, A. 1907. Sylloge Myxophycearum; in De Toni's Sylloge Algarum 



omnium, Vol. V. 

 Gardner, N. L. 1906. Cytological studies in Cyanophyceae. Univ. of 



CaUf. Pub. Bot., 2: 237-296. 

 Hyams, Isabel F., and Richards, Ellen H. 1901, 1902, 1904. Notes on 



Oscillatoria prolifica. Tech. Quarterly, Vols. 14, 15, 17. 

 Klrchner, O. 1900. Schizophyceae; in Engler-Prantl Nat. Pflanzenfamilien. 

 Olive, Edgar W. 1904. Mitotic division of the nuclei of the Cyanophyceae. 



Beihefte z. Botan. Centralb., 18: 9-44. 

 1905. Notes on the Occurrence of Oscillatoria prolifica in the Ice of Pine 



Lake, Waukesha County, Wisconsin. Trans. Wis. Acad. Sci., 15: 124-134. 

 Oltmanns, Friedr. 1904-05. Morphologic und Biologie der Algen. 2v. 



Jena. 

 TiLDEN, Josephine. 1910. The Myxophyceae of North America and Adja- 

 cent Regions, etc. Minneapolis. 

 West, G. S. 1904. A Treatise on the British Frcshv/ater Algae. Camb. 



Univ. Press. 

 WOLLE, F. 1887. Fresh-water Algae of the United States. Bethlehem, Pa. 



