Ihe practice of agriculture has received great benefits from scientific investigation 

 of the cycle of chemical changes on land, by agricultural chemists, plant physiologists, 

 bacteriologists, animal physiologists and by distinguished advocates of agricultural economy. 

 It is now a question of utilising the experience and the results of investigation gained 

 on land for an economy of the sea. It is self-evident that in this, we must take 

 account of the special conditions which the organisms living in water experience as con- 

 trasted with the life surrounded by air. 



As many results of science have already been adopted with advantage in the management 

 of ponds, we may be allowed to expect that similar principles can be introduced into the 

 management of the sea, in such a way that the natural production can be helped out in 

 the most rational manner possible. For all investigations which have as end the ascer- 

 taining of the productivity of a given area of water, a knowledge of the organic and 

 inorganic changes in the sea and the discernment of the natural relations between pro- 

 duction and conditions of production are quite indispensable. We have to thank V. Hen se n^ 

 for the advancement of the aims and for the methodical grounding of all general marine 

 biology. As I myself have been engaged in this field for 17 years, 1 have taken some 

 pains to advance this branch of study as much as possible after the opportunity offered 

 itself, with the organisation of the international investigations of the North-European seas, 

 to make some voyages in the North Sea and Baltic on a German research-steamer, well 

 equipped for scientific work, and to investigate some questions of general importance with 

 the help of colleagues, also to improve the already existing methods so as to obtain 

 results free of error. 



Just as on land, the true production in the sea, that is, the formation of new 

 organic substance, arises exclusively from plant-life. It is only the plant which, owing 

 to the possession of chlorophyll, can form organic materials from inorganic (carbonic acid, 

 water and a number of salts) in the presence of light. The animals on the other hand, 

 are all consumers ; they must all take the organic materials necessary for the building up 

 of the body and the maintenance of life from the plant-kingdom. On the death of animals 

 and plants the complex organic substances which composed their bodies, break down again, 

 in consequence of the activity of certain bacteria, into the same simple inorganic materials 

 from which the plants construct organic substance. 



The determination of the true production depends therefore entirely on the plants, 



' Ueber die Bestimmung des Planlttons oder des im Meere treibenden Materials an Pflanzen und Tieren. 

 (5. Bericht d. Komm. z. wiss Unters, d. deutscli. Meere. 1887). 



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