452 ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 



But if we examine the results of analyses of these media for alkalinity 

 a probable explanation presents itself. The following figures are only 

 comparative : — 



A — 38 mgrm. OH °/^^ (used as standard). 



B — 37 „ „ (higher than usual). 



C — 16 „ ,, (very Ioav indeed). 



D-34 „ 



It will be seen that the amount of growth in each treated sample 

 follows the alkalinity very closely. 



Solutions of NaoCOg, NaHCOg and HCl were made up, so that 4 cc. 

 of any one contained an amount of acid or alkali equivalent to 

 10 mgrm. OH. From these a series of normal Miquel sea-waters of 

 different alkalinities were prepared. Cultures of Thalassiosira de- 

 cipicns were grown in these media. 



A. Normal Miquel sea-water. Control. A ^ 32*7 mgrm. OH 7oo- 



Perfectly normal groAvth. 



B. Ditto + 4 cc. Na.^C03 per litre. A = 41 -7 mgrm. OH 7^^ ( = -t- 9-0).* 



No difference between this culture and A. 



C. Ditto + 8 cc. ^XCOo per litre. A = 50-2 mgrm. 0H7„^ (= + 17-5). 



Best culture in series in quality and quantity. 

 D Ditto + 4 cc. NaHCOg per litre. A - 42*4 mgrm. OH 7'^^ ( = + 9-7). 

 Slightly better than control. 



E. Ditto + 8 cc. NaHCOo per Htre. A = 51 -5 mgrm. OH 7^^ ( = + 18-8). 



As D. 



F. Ditto -1- 4 cc. HCl per litre. A = 22-2 mgrm. OH 7„„ ( = - 10-5). 



Fair growth but never up to control, exhausted much sooner. 



G. Ditto + 8 cc. HCl per litre. A = IM mgrm. OH 7^„ ( = - 21 '6). 



Poorest in series. 



Except in the cases where the alkalinity was lowered by the addition 

 of HCl, the results obtained from this series were not up to expecta- 

 tion. Nevertheless the majority showed a distinct improvement from 

 increased " alkalinity " and in C, where the alkalinity had been raised 

 17"5 mgrm. OH7oc5 this improvement was very marked. 



Another point illustrated by cultural experiment is that in two 

 samples of an. char, water, one with " outside " and the other with 

 " tank-water " as a basis, the amount of growth in the latter consider- 

 ably exceeded that in the former, and at the same time it was found 

 that, with the tank-water, the alkalinity had not been reduced to the 

 same extent as in the case of the outside water. 



How far apparently anomalous results, which have so frequently 



* Figures in parentheses are diirerence in alkalinity from control, in mgrm. OH 7oo* 



