EXPERIMEXTAL CULTURES OF DIATOMS 63 



V. 



Experimental Cultures of Diatoms occurring near 

 St. Andrews, N.B. 



By Clara W. Fritz, B.A., M.Sc, 

 Principal of East Angus Academy, Quebec. 



INTKODUCTION. 



In the summer of 1916 cultures were set up at the Atlantic Biological Station 

 with the object of providing food for marine copepods. The particular species sought 

 was Nitzschia closterium, but owing to its rare occurrence it was found necessary to 

 make trial of other forms. I have since found, however, that when present Nitzschia 

 closterium grows with great luxuriance, will in a mixed culture rapidly replace 

 many forms and is persistent. 



The results of the work of 1916 have already been recorded, and as the nutrients 

 used by Allen and Nelson (9) were found beneficial, they were again employed. 



Solution A. Dissolve 20.2 potassium nitrate in 100 c.c. distilled water. 



Solution B. Dissolve 4 g. sodium phosphate in 40 c.c. distilled water. Add 2 c. c. 

 pure concentrated hydrochloric acid, then 2 c. c. ferric chloride dissolved by gentle 

 heating. Add 4 g. calcium chloride dissolved in 40 c.c. distilled water. 



These solutions were used in the proportion of 2 c. c. of A and 1 c. c. of B per litre 

 of sea water. The precipitate thrown down by B, containing most of the iron, a little 

 phosphorus and some calcium, was allowed to settle and then removed. The sea water 

 used was first raised to 70° C. and maintained at that temperature for 30 minutes 

 in order that all plant life might be destroyed. 



Mixed Cultures. 



Plankton was collected on July 4, 1917. The collection contained nineteen 

 species, of which the prevailing forms were Chaetoceras dehile and Thalassiosira 

 nordenshioldii. In the hope of more efi'ectively isolating individual species than in 

 previous work a method of subdivision in test tubes was employed. A tube of prepared 

 sea water was inoculated with two drops of plankton and divided into six test tubes. 

 The contents of each was then added to an erlenmeyer flask of 125 c. c. volume, which 

 had been half filled with prepared sea water. Three series were arranged and with 

 each a control in untreated, sterilized sea water was run. The sets were placed in: 

 (1) a window receiving afternoon sun, (2) a window receiving no sun; (3) flasks 

 covered with cheesecloth. 



No development was obtained in the untreated water except in one flask in 

 position 2 ; and this was very slight and disappeared in ten days. In position 1, three 

 flasks produced each a mixed culture of Thalassiosira nordenshioldii and STceletonema 

 costatum. These were at their height on July 18, after which one became exhausted 

 and the other two presented Nitzschia closterium and Melosira hyperhorea. On 

 August 6 these forms were showing rapid increase and on August 25 when the work 

 was closed at the Biological Station were in excellent condition. New flasks were 

 inoculated from these and formed the source of material for winter studies. 



In position 2, five mixed cultures were obtained and one pure culture referred to 

 later. Thalassiosira nordenshioldii was always the dominant form, but was accom- 



