APPENDIX D: BRANDT — 8 — 



nitrogen occurs in the western Baltic. Even in the case of the greatest quantity of 

 albuminous nitrogen yet found, the quantity of fixed nitrogen occurring in inorganic form, 

 is at least four times greater than that in the_ other form. 



For land-plants, such an extensive absorption of the food-stufFs, which must be taken 

 from the ground through the roots, is impossible. It is also known, that the absorption- 

 coefficient as regards nitrogen compounds, amounts to only a few per cent for the land- 

 plants. That the small plankton-algae can use up the food-stuffs to such an extraordinarily 

 greater degree, is readily comprehensible when we consider, that they float in a solution, 

 even though weak, of plant-food, that they take up the food-stuffs over their entire, 

 relatively very large surface and that they are in general distributed in the upper, light- 

 illuminated water-layers in a sufficiently uniform manner so as not to disturb one another too 

 much in the absorption of the food-stuffs of their immediate surroundings. We may 

 believe that the absorption-coefficient e. g. for nitrates, is greater than 50 "lo. Conse- 

 quently, the nitrogen compounds will be in sufficient quantities in general in the northern 

 seas, even though it is not altogether excluded, that they may occur in minimum quantity 

 at many seasons and under special conditions. 



It is quite different in the warm seas. It is a very striking fact, that the plankton- 

 organisms occur, not in very much greater, but to all appearance in smaller, quantities 

 in the tropical than in the colder seas in spite of better light and higher temperature, 

 though we might expect and it has many times been asserted that they did. I have 

 endeavoured in an earlier paper to explain this by the following hypothesis': 



"If the denitrifying bacteria of the sea, like the closely investigated denitrifying bacteria 

 of the land, develop a strongly disturbing activity at higher temperatures, only a relatively 

 small production would take place in the warm seas in spite of much more favourable 

 conditions (according to the law of the minimum), owing to the great disturbance amongst the 

 indispensable food-substance; whilst, in the cold seas, more nitrogen compounds would be 

 at the disposal of the producers owing to the retardation or suppression of the disturbing 

 process." It is necessary, therefore, to seek for the denitrifying bacteria in the sea and 

 determine at what temperature they are most active. The first investigations have been 

 made by Erwin Baur-, who showed that denitrifying bacteria with a high temperature- 

 optimum occurred in Kiel Bay. By means of different culture-methods. Gran** has also 

 discovered several species of another group of denitrifying bacteria on the Dutch coast. 

 The German quarterly cruises gave us, later, many opportunities to add to and determine 

 the wide distribution and relative abundance of both groups of denitrifying bacteria in the 

 open North Sea and Baltic *. 



Sterilised culture-solutions according to the methods of Baur and Gran, were mixed 

 during the cruises with I cc. of water or a small sample of the bottom-soil. These rough 

 cultures taken at different seasons of the year showed different results. The Baltic was 

 always found to be richer in these disturbing bacteria than the North Sea. In August 



' Ueber den Stoffwechsel in Meere 1. u. 2. Abhandlung (I. c). Ueber die demnächst beginnenden inter- 

 nationalen Untersuchungen der nordischen Meere (Verhandl. V. Internat, zoolog. Congress. Berlin 1901). 



' Ueber zwei denitrifiziereude Bakterien aus der Ostsee 1901. (Wiss. Meeresunters. Kiel. VI). 



^ Studien über Meeresbakterien I. (Bergens Museums Aarbog 1901. Nr. 10). 



* R. Feitel, Beiträge zur Kenntnis denitrifizierender Meeresbakterien (Wiss. Meeresunters. Kiel. VU. 

 1903). K. Brandt, Ueber die Bedeutung der Stickstoll'verbindungen für die Produktion im Meere (Beihefte z. 

 Botan Centralblatt. XVI. 1904). 



