114 



Bacillariese 



formed within the old ones. The resting-spores of diatoms are really 

 aplanospores, in every way comparable with those which occur in many 

 groups of the Chlorophycese. 



CULTURES. The most extensive culture experiments have been in con- 

 nection with plankton-diatoms. Miquel ('92 '98) 

 conducted a large series of experiments with a view 

 to obtaining cultures of single species of diatoms 

 and obtaining information concerning the conditions 

 requisite for their rapid increase. His methods were 

 devised in the first instance for freshwater diatoms, 

 but were afterwards found by him to succeed with 

 marine littoral species. For the culture of marine 

 diatoms Miquel prepared a special medium. Two 

 solutions were made up as follows : 



Solution A. Magnesium sulphate lOgrm., Sodium 

 chloride lOgrm., Sodium sulphate 5 grm., Ammonium 

 nitrate 1 grm., Potassium nitrate 2 grm., Sodium 

 nitrate 2 grm., Potassium bromide 0*2 grm., Potassium 

 iodide 01 grm., Water 100 grm. 



Solution B. Sodium phosphate 4 grm., Calcium 

 chloride (dry) 4 grm., Hydrochloric acid 2 cc., Ferric 

 chloride 2 cc., Water 80 cc. 



Forty drops of solution A and from 10 to 20 

 drops of solution B were added to every 1000 cc. 

 of sea- water which had been sterilized by keeping it 

 at 70 C. for about 20 minutes. Miquel also added 



a small quantity of sterilized organic matter. Good cultures were obtained 

 in this medium, and cultures of single species of diatoms were obtained by 

 fractional subdivision. 



Allen & Nelson ('00) have also obtained excellent results by this 

 method, which they say is certain and gives good cultures. These authors 

 have also used with great success a modification of Miquel's culture medium. 

 It was found possible to reduce the first solution to one of potassium nitrate 

 without detriment, the two solutions being as follows : 



Solution A. Potassium nitrate 20'2 grm., Distilled water 100 grm. 

 Solution B. Sodium phosphate (Na 2 HPO 4 . 12H 2 0) 4 grm., Calcium 

 chloride (CaCl. 2 6H 2 0) 4 grm., Ferric chloride (melted) 2 cc., Hydrochloric 

 acid (pure, concentrated) 2 cc., Distilled water 80 cc. 



2 cc. of solution A and Ice. of solution- B are added to each lOOOcc. 

 of sea-water, and the whole sterilized by heating to 70 C. When cool 

 the clear liquid is decanted from the precipitate which forms when solution B 



Fig. 83. A cell of Surirella 

 spiralis Kiitz. with eight 

 thick- walled resting-spores. 

 The detailed structure of 

 the valve is not indicated. 

 x400. 



