PELAGIC PLANT LIFE 385 



breathing, and also to supply building material for their growth 

 and propagation. Putter has endeavoured to find out whether putter. 

 organic matter dissolved in the sea-water does not provide this. 

 He investigated its amount, and got surprisingly high values. 

 Improved methods have enabled Raben to check his experi- 

 ments ; in water from Kiel there were 10.9 to 13.9 milligrams, 

 or on an average 12.25 milligrams, of organic combined carbon 

 per litre of sea-water, and at a station in the Baltic 3 milligrams. 

 These are really high values, if we compare them with the 

 quantities of organic substance we are able to point to in the 

 form of living organisms. Lohmann's studies show that the 

 total amount of the organic combined carbon in the plankton at 

 Laboe in Kiel Bay varied during the year between 12.7 mg. 

 and 1 89.8 mg. per 1000 litres of sea- water. According to Raben's 

 investigations at a place close by, the mean value of organic 

 combined carbon in dissolved form is 12,250 mg. per 1000 litres, 

 or in other words about sixty times as much. 



Too little is known, unfortunately, about the occurrence of 

 organic matter, and there are many difficulties to be overcome 

 before we can look for conclusive results. Perhaps the most 

 discouraging thing is that even the best filters allow a good 

 many organisms to pass through them. The water-samples 

 to be examined ought possibly to be freed from all suspended 

 insoluble matter by means of the centrifuge, but even this 

 method will not always give entirely satisfactory results, since 

 some of the algae (cyanophycese, Halosphcp.ra) are lighter than 

 sea-water, while the nimbler animals will swim up from the 

 bottom before one can separate the clear water from the 

 deposit. Putter's hypothesis, however, certainly deserves to 

 be further tested. If it be really true that in the salt-water of 

 the open sea there is organic substance in sufficient quantities 

 to be compared with what is combined in plants and animals, 

 then this substance must be due to the production of plants. 

 We will accordingly be forced to conclude that the pelagic 

 algse distribute to their surroundings through their surface 

 comparatively large quantities of organic substance, and that 

 their production is thus in actual fact much more consider- 

 able than we are led to believe, when we merely measure what 

 they store up in their cells during growth and augmentation. 

 Even if it seems strange biologically that they should evince 

 such want of economy in regard to valuable nutritive matter, 

 it would be unwise to reject the hypothesis, and the best plan 

 is to await the results of continued investigations. Some 



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