i 9 6 SCIENCE PROGRESS 



of light is much the same for both. Therefore one might expect 

 that the abundance of life in the seas in the polar regions would 

 not fall off so much as on the land. But so far from this 

 being the case the polar seas actually possess as much life as 

 the equatorial ones, and indeed it is apparently the case that 

 both the marine fauna and flora increase in abundance as we 

 pass from the equator to the frigid zones. Evidently other 

 factors than the distribution of temperature and light must 

 affect the abundance of life. What are they ? " One stands," 

 says Kjellmann, "as before an insoluble problem, when he 

 obtains a luxuriant vegetation from the depths of the sea, and 

 this when the temperature of the air is extremely low ; when 

 the surface of the sea is covered with a thick sheet of ice ; 

 and when nocturnal gloom prevails, even at noonday." x 



The cause can only be that some indispensable foodstuff 

 of the plants is more abundant in the colder seas than in the 

 warmer ones. We need only consider the plants, for it is 

 only these organisms that can form living substance from 

 inorganic materials, and we know that the animals can only 

 utilise as food the organic substance of other living things. 

 Now what is this substance which is less abundant in the 

 tropical and warmer seas than in the colder ones ? Although 

 a plant may require a number of foodstuffs for its main- 

 tenance and propagation, }^et it does not matter in what 

 proportion the most of these are present so long as one of 

 them is absent or is present in minimum quantity. If this 

 one indispensable foodstuff is absent then the production 

 ceases, and if it is present in small amount then the production 

 is also small. We may compare the "Law of the Minimum" 

 with the strength of a chain which depends on the strength 

 of the weakest link. 



Now the "producers of the sea" are chiefly the diatoms, the 

 peridinians and some of the flagellate protozoa, and we are only 

 concerned with the conditions of nutrition of these organisms. 

 They require many foodstuffs, but we may narrow down the 

 inquiry to the three substances — compounds of nitrogen (nitrous 

 and nitric acids and ammonia and the salts of these), silicic 

 acid, and phosphoric acid. Oxygen and carbonic acid are also 

 required, but the former gas is never absent in the sea, and is 



1 Brandt, "U. d. Stoffvvechsel im Meere," 2 Abhandl. Wiss. Meeresunt. Kiel. 

 Komm. Bd. 6, Kiel, 1902. 



