186 MANUAL OF POISONOUS PLANTS 



gether like a row of lozenges. A few of the cells fall out of the sheath form- 

 ing what is called a hormogonium. This starts a new filament which has a 

 characteristic movement hence the name Oscillatoria. Oscillatoria is common 

 in hot springs sometimes also covering damp soil in greenhouses. It is mainly 

 through decomposition that these algae become noxious. 



NOSTOCACEAE 



Cells spherical in unbranched chains frequently torulose; sheaths gelatinous 

 frequently forming jelly-like masses; reproduction by hormogonia and spores. 

 Many species of the order are troublesome in water supplies. Some species 

 of the genus Nostoc are used as food. 



Nostoc, Vaucher 



Colonies in flexuose chains united in definite gelatinous investment; cells 

 usually spherical or ellipsoidal; heterocysts terminal or intercalary; spores 

 spherical or oblong. These algae are very common in the lakes in southern 

 Minnesota, Northern Iowa, and elsewhere in the United States. By decomposi- 

 tion, Nostoc produces disagreeable products. Dr. Arthur, some time ago, found 

 Nostoc in quantities in the lakes of southern Minnesota and at one time it was 

 supposed one species produced poisoning of cattle. Dr. Arthur, however, did not 

 attribute the poisoning to this alga. One of the species of this genus frequently 

 found is Nostoc verrucosum common in both the Old and New World. 



Anabaena, Bory 



Filaments straight or curved, surrounded by a thin sheath united to form 

 a fiocculent mass ; heterocyst and spores intercalary. This alga also forms 

 filaments which are free or united in a mass. In the filaments occur the vege- 

 tative cells, the heterocysts, whose function is not known, and a spore which 

 serves to start the organism again. This organism causes much annoyance 

 in water, not only in North America but in Europe. Dr. Farlow some years 

 ago referred to its injurious properties. It has also been frequently mentioned 

 by Parker as contaminating water supplies in Massachusetts; others have no- 

 ticed it in New York, and Dr. Trelease has found it in Madison, Wisconsin. 

 The latter writer says in speaking of the Waterbloom and other algae : 



After a warm spring, on my return to Madison, June 26, 1887, I observed a considerable 

 quantity of putrid scum on the shore of Fourth I^ake, but the south wind scattered it before 

 specimens of it could be obtained. The succeeding fortnight was hot, and after a couple of 

 calm days, succeeding a strong wind from the north-west, the southern half of the lake 

 was filled with suspended particles about a millimeter in diameter. These consisted exclusive- 

 ly of Anabaena HassaJlii, already in full fruit; the spores were the customary Sphaerozyga 

 arrangment, in a collection made June 20th. 



This algae is common in many of our northern lakes and is a frequent 

 pest in water reservoirs, producing pig-pen odors and bad taste of water. 



RIVULARIACEAE 



Filiform filaments attenuated from base to apex, heterocysts basal or rarely 

 absent; sheath tubular, gelatinous, or membranous . 



Gloeotrichia, J. Ag. 



Free floating colonies solid when young but inflated and hollow when 

 old; the filaments radiating from the centre outwards. 



