APPENDIX D: BRANDT _ 6 — 



from the ground, like land- plants and sea-grass — the only marine blossoming plant, but 

 from the surrounding water. This holds good for all algae, for the small floating plankton- 

 algae as for the ground diatoms and the larger fixed algae. The food of the algae, of by far 

 the great majority of marine plants therefore , must consequently occur in dissolved 

 condition in the water, and the sea-water itself is like a very weak solution of plant-food, 

 which contains all the inorganic materials necessary for the formation of organic substance. 



If we consider the composition of the sea-water on the one hand and that of marine 

 plants on the other, we find that there are but few isolated inorganic substances; and 

 these are available for the plant-life in such relatively small quantities, that they — having 

 regard to the law of the minimum — command the amount of the production in the sea. 

 The substances of chief importance, according to the present state of our knowledge, are 

 the inorganic nitrogen compounds (ammonia, nitrites and above all nitrates), salts 

 of phosphoric acid and silicic acid. Very small quantities of these food-stuffs occur 

 in sea-water, of many indeed only traces. For the building-up of organic substance in 

 marine plants, the silicic acid is much more necessary than the nitrogen compounds, and 

 these again are required in greater degree than the phosphates. Exact chemical analyses 

 have therefore to be made with regard to the composition of the principal plankton-plants, 

 in order to learn, how much they require of these food-materials which occur in traces. 

 Further, detailed investigation is necessary concerning the content of sea-water in regard 

 to these rare food-materials, in order to judge how poverty in the one case, richness in 

 the other, may arise. Lastly, simple experiments are also wanted to test the correctness 

 of the conclusions, which have already been won from the chemical analysis of the 

 organisms and of water. According to the methods used in modern agriculture (e. g. 

 by employing a method recommended by Zuntz' for fresh-water ponds), we can determine 

 the food-stuffs which are especially favourable to the growth of the various forms, and 

 which of the food-stuffs is present in minimum quantities at certain times and in a certain 

 region of water, by adding the separate food-stuffs, which possibly are present in minimum 

 quantities, to the sea-water containing living plankton-plants to be investigated. The 

 results of these three series of investigations must agree with one another. Also, for the 

 further elucidation of the results gained, we require to have bacteriological investigations, 

 investigations of the bottom and also of the composition of the water in general, in addition 

 to the usual hydrographical investigations. 



Of these manifold investigations, which are quite indispensable for a deeper insight 

 into what is going on in the sea, only a portion could at first be carried out. Above all, 

 it is necessary to improve the methods for the quantitative determination of very small 

 quantities of nitrogen compounds, also of silicic acid and phosphoric acid and to such 

 an extent that trustworthy information may be gained regarding the horizontal and vertical 

 distribution of these food-stuffs and their dependence on the seasons of the year. 

 Investigation The grcatcst difficulties are presented by the nitrogen compounds, ammonia, nitrites 



°comp"ou'n'ds" '^"*^ uitratcs, which must be distinctly separated as much as possible. In his work recently 

 published, on the method of the quantitative determination of nitrogen compounds in sea- 

 water. Dr. Raben^ has also given a number of values for the quantities of nitrogen 



' K. Knauthe, Die Karpfenzucht. Neudamm 1901, p. 147 et seq. 



^ E. Raben, Uebçr quantitative Bestimmung von Stickstoffverbindungen im Meerwasser, nebst einem 

 Anhang über die quantitative Beslimmung der im Meerwasser gelösten Kieselsäuie. (Wissensch. Meeresunters. 

 Vlll. Kiel 1904). 



