SEA-FISHERIES LABORATORY. 249 



did not exist, then the whole depth of the sea in process of 

 ages of time would come into complete equilibrium with the 

 air, and the dissolved carbon-dioxide would be the same in the 

 upper layers and in the depths, and accordingly there would be 

 no drop in alkalinity in the deeper zones. 



The slow drop in alkalinity demonstrates an effect of 

 photo-synthesis, but it is so small within the upper portions 

 that it may unquestionably be taken that photo- synthesis, 

 aided by convection currents, has the full alkalising effect for 

 at least 100 metres from the surface. 



This supposition leads to a photo-synthetic effect of 

 300,000 kilograms of dry organic matter such as carbohydrate 

 per square kilometre. 



Expressed in English measurement this amounts to about 

 two tons of dry organic matter per acre, and since vegetable 

 crops do not contain on an average more than 20 per cent, of 

 dry organic matter, this ocean crop corresponds to at least 

 ten tons of moist plant organisms per acre. 



The factors entering into such a computation, in the 

 present fragmentary state of our knowledge, are of course 

 vague, but the above is certainly a minimum, and it becomes 

 obvious that the sea has annually a vast crop of green-plant 

 organic matter comparable to that growing in the fields on 

 land. 



Another interesting point arising from these alkalinity 

 determinations is that the degree of photo-synthesis and the 

 corresponding weight of ocean crop is probably much more 

 abundant nearer to the littoral. It is frequently observable 

 in the table, that water taken along shore is more alkaline than 

 that taken from on board a vessel three to five miles from 

 shore. 



Observations at great distances out at sea during the 

 various seasons are most desirable but difficult to obtain. 



