ARTIFICIAL CULTURE OF. MARINE PLANKTON ORGANISMS. 401 



a probable explanation presents itself. The following figures 

 are only comparative : 



A. 38 nigrm. OH°/QQ(used as standard). 



B. 37 ,, ,, (higher than usual), 

 c. 16 „ „ (very low indeed). 

 D. 34 ,, „ 



It will be seen tliat the amount of growth in each treated 

 sample follows the alkalinity very closely. 



Solutions of NaoCOs, NaHCOs and HCl were made up, so that 

 4 c.c. of anyone contained an amount of acid or alkali equiva- 

 lent to 10 mgrm. OH. From these a series of norinal Miquel 

 sea-waters of different alkalinities were prepared. Cultures 

 of Thalassiosira dec ipi ens were grown in these media. 



A. Normal Miquel sea-water. Control. A = 32*7 mgrm. 



OH 7 



oo- 



Perfectly normal growth. 

 B. Ditto + 4 c.c. NaoCOs per litre. A = 41*7 mgrm. 

 OH -/,,(= -r 9-0). 1.. _ 

 No difference between this culture and A. 

 c. Ditto + 8 c.c. NaoCOs per litre. A = 50*2 mgrm. 

 0H°/,, (= + 17-5). 

 Best culture in series in quality and quantity. 



D. Ditto + 4 c.c. NaHCOg per litre. A = 42-4 mgrm» 



^0H7oo(= + 9-7). 

 Slightly better than control. 



E. Ditto + 8 c.c. NaHC03 per litre. A = 51-5 mgrm. 



OH7oo(= + 18-8). 

 As D. 

 p. Ditto + 4 c.c. HCl per litre. A = 22-2 mgrm. OH 



- . 7oo(= - 10-5) • 



Fair growth, but never up to control ; exhausted 

 much sooner. 

 G. Ditto + 8 c.c. HCl per litre. A = IM mgrm. OH 

 %, (= - 21-6). 

 Poorest in series. 



^ Figures in parentheses are difference in alkalinity from cont-rol, 

 in mgrm. OH °/go. 



