ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 387 



additive effect on tlie sea-water is, therefore, a sliglitly in- 

 creased concentration of phosphate and calcium. 



An analysis of a sample of tank- water for phosphorus, 

 before and after treatment with solution B (1 c.c. per 1000), 

 gave the following figures : 



Tank-water '5 nigrm. P per litre = "OOlOo grm. P0O5. 



Tank-water + solution B (without precipitate) TS mgrm. P 

 per litre = '00488 grm. P0O5. 



It will be noticed that the figures from the different 

 analyses do not agree very well. This is probably due to 

 the fact that different samples were used for analysis in each 

 case, and also to the fact that the solutions were made up in 

 the ordinary way, without any special precautions, volumes, for 

 instance, being measured in cylindrical glasses, pipettes, etc. 



Cultures were tried in sea-water containing the normal 

 amount of solution A, plus the normal constituents of solution 

 B, less all the iron and less the amount of phosphate that would 

 combine with the iron to form basic ferric phosphate (PoO- 

 2Feo03l2H20). This solution should have very nearly the same 

 chemical composition as normal Miquel sea-water from which 

 tlie precipitate has been removed. Successful cultures could 

 not, however, be obtained in it. Neither could cultures be 

 grown in sea-water to which had been added the normal 

 amount of solution A and 1 mgrm. P (as sodium phosphate) 

 per litre. 



To ascertain the effects of the different constituents of 

 solution B, experiments were carried out with separate solu- 

 tions of these constituents, each of the same strength, as in 

 Miquel's formula. Different combinations of these solutions 

 were added, together with solution A, to sterilised sea-water, 

 and the resulting media were inoculated in the usual way. It 

 was found necessary to repeat these exjDeriments a great 

 number of times, as the results obtained were rather contra- 

 dictory. To illustrate the methods used a list of the ditt'erent 

 media, and notes of the cultures obtained in them, are given 

 below. These media wei*e inoculated from cultures of 

 Thalassiosira decipiens, and the cultures were kept 



