248 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



an approximation the carbon be assumed to be all converted 

 into carbohydrate, then some calculation may be given to 

 demonstrate what such figures mean. 



The amount of 8-8 milligrams per litre of carbon-dioxide 

 changed corresponds to 24 milligrams of organic carbon, and 

 this is 6 milligrams per litre of carbohydrate, synthesised, or 

 6 parts in a million of the sea-water — at first sight a 

 ridiculously small quantity, but it is spread out in the sea. 

 Six milligrams in a litre gives 6 grams in a cubic metre of sea- 

 water. If the change by photo-synthesis occurred to only a 

 depth of one metre, this would mean on a square kilometre of 

 sea surface 6 millions of grams, or 6,000 kilograms of carbo- 

 hydrate synthesised. 



But the change occurs for a distance down in all probability 

 of some hundreds of metres instead of one metre. Convection 

 currents, winds and tides, mix the water thoroughly up for 

 many metres deep. 



The careful observations of Sven Palitzsch 4 have proved 

 that the alkalinity of the sea-water does decrease as the depth 

 from the surface increases, but there is scarcely any appreciable 

 decrease at 100 metres, and even at 400 metres the decline is 

 usually still small. 



This decline in alkalinity at greater depths is of interest 

 as an evidence of photo-synthetic activity and its relationship 

 to alkalinity of the water. Its cause is probably three-fold, 

 first the photo-synthetic activity decreases with depth as the 

 intensity of the light diminishes in traversing the water ; 

 secondly, with increasing depth there is less admixture by 

 currents with the more alkaline water due to photo-synthesis 

 of the upper layers ; and thirdly, organic debris of plant and 

 animal in descending becomes oxidised, and these oxidations 

 again set free carbon- dioxide which lowers in turn the alkalinity 

 of the water. 



If it be supposed, for the moment, that photo-synthesis 



