Panning: ALG^E OF THE ST. PAUL CITY WATER. 611 



Synedra and Asterionella. Of the Chlorophyceae, Scenedes- 

 mus and Raphidium were present most of the time. Among 

 the Cyanophycere, Oscillatoria and Ccelospharium were prac- 

 tically constant. 



The effect of the cold on some of the varieties is shown by 

 the accompanying plates (PI. XLIII. and XLIV.). It will be 

 seen that a fall in temperature coincides with a decrease in the 

 numbers of all except Oscillatoria, which shows a gradual in- 

 crease with the cold and is abundant for several weeks during 

 the severest weather. 



The desmids, more plentiful in the fall than at any other 

 time, although never abundant, disappeared after the cold wave 

 of the third week in December. Another fall in temperature 

 about the fourth week in January banished most of the Chloro- 

 phyceae and cleared the field of Ccelosphcerium, but some of the 

 diatoms persisted until the zero weather in February, when 

 most of them disappeared. Fragilaria was abundant in Jan- 

 uary and about January 3Oth, when Oscillatoria and Fragilaria 

 were practically the only forms seen, the water contained con- 

 siderable sandy debris and entangled in it were quantities of 

 resting spores of Glceotrichia. 



The observations vary from year to year so that a record 

 should be kept for several years before one could find what 

 forms were both constant and abundant. For example, in the 

 fall of 1898, Anabcena was " common," but in the following 

 year it is only marked " present." 



I wish to thank Mr. P. F. Lyons, of the St. Paul Weather 

 Bureau and Mr. John Caulfield, Secretary of the Water Board, 

 St. Paul, for their kind assistance. 



EXPLANATION OF PLATES XLIII. AND XLIV. 

 Table showing relation between abundance of certain forms and 

 temperature. XLIV. is a continuation of XLIII. 



PLATE XLV. 



1 . Coelastrum microporum Naeg. var. speciosum Wolle. Freshw. 

 Algae U. S. 170. pi. 156. f. 4. 1887. 



2. Pediastrum duplex Meyen Beob. iiber Algenformen. in Nova 

 Acta Acad. Leop. Carol. 772. 1829. 



3. Scenedesmus quadricauda (Turp.) Breb. Alg. Falais. 66. 1835. 



4. Scenedesmus bijttgatus (Turp.) Kg. Syn. Diat. 607. 1833. 



5. Rhaphidium polymorphum Fresen. var. aciculare (A. Br.) 

 Rabenh. Fl. Eur. Algar. 3: 45. 1868. 



