504 LIFE IN THE OCEAN. 



In the Mediterranean, at the Straits of Messina, l>v Lohmann. 



In the Tropics, the Roads of RaUim in New Pomerauia (formerly New 

 Brittania). in latitude 4 S., b}' Dahl. 



(c) During the winter months (1888-89): 



In the Bay of Naples, by Schutt. 



Second. On the high seas, by a series of drafts during the course 

 of voyages of exploration: 



In the Baltic (from Memel to Gotland): in the northern part of 

 the German Ocean, from Skagen to the Hebrides; in a great part of 

 the Atlantic during the Plankton expedition (from the middle of July 

 to the beginning of November, 1889); in the part of the sea between 

 the Lofoden Islands and the north of Spitzbergen during the Prince of 

 Monaco expedition, in July and August, 1898. 



I shall here leave out of consideration the numerous results which 

 these observations have furnished in zoology, zoogeography, and 

 oceanography, and confine myself to two points. The first is that 

 shallow seas are richer in plankton than deep seas are, and that among 

 the latter the Saragasso Sea is particularly poor (in August). The 

 explanation of this is to be sought in the law of the minimum. In 

 soundings, the intiuence of the soil and of the land with its contribu- 

 tions is more sensible, and plants find in a less mass of water a rela- 

 tively great quantit}" of inorganic substances which, in the depths of 

 the ocean, are more scattered and are specially deficient in the upper 

 layers, where alone vegetation is possible. The substances in the 

 unlighted depths can not be directly used ]\v plants. On the other 

 hand, as the great currents of the ocean extend along the coasts they 

 bring to the upper laj^ers of the high seas new food for the plants, so 

 that these layers may be relativelv more productive than the Saragasso 

 Sea, whose waters are still and in the middle of which the conditions 

 of alimentation appear to be altogether unfavorable. 



It would be important to ascertain by chemical investigations which 

 of the substances susceptible of feeding vegetation exists in smallest 

 amounts. It is probably combined nitrogen. The results mentioned 

 above, as furnished by fish ponds, lead toward this conclusion. In the 

 same line are the experiments of Apstein on the lakes of Holstein, 

 experiments which I have verified, showing that lakes rich in plankton 

 contain much nitric and nitrous acids, while lakes poor in plankton are 

 also poor in nitric acid, the c^uantity of plankton and the percentage 

 of nitrates being sensibly proportional. 



The second point to which I wish call attention in the results of 

 the quantitative stud}^ of plankton — and it is the more striking of the 

 two — is that tropical seas and the temperate zones are relatively poor 

 in plankton, while the Arctic Ocean is rich. On land it is just the 

 reverse. Luxuriant vegetation and superabundance of animal life are 



