LIFE TN THE OCEAN. 505 



charartoristic of the Tropics and mightily contrast with the meager 

 vegfetation and sparse population of the polar solitudes; and one wotdd 

 expect beforehand to iind the same contrast in marine life. Plants 

 for example, need light to produce organic matters. Now, tropical 

 seas are better lighted than glacial seas. High temperatures, too, are 

 favorable to the development of marine organisms. Finally, the extra- 

 ordinary variety of forms in tropical seas seems to argue greater 

 wealth. Without Hensen's methods we should not have suspected 

 the remarkable fact mentioned. 



First of all. we must make sure that the results of the Plankton 

 Expedition are correct. This expedition only drew its samples during 

 a part of the year, so that it might be that at other seasons the rela- 

 tive poverty of the tropical seas would be transformed into great 

 wealth. In order to ascertain how much there was in this objection, 

 observations were made on different coasts in very different latitudes 

 during a whole year, while at the same time as many additional obser- 

 vations as possible were made in deep Avater. We thus tind at our 

 disposition numerous observations made in the three oceans at my 

 solicitation, by the Messrs. Schott, of Hamburg; Captain Bruhn. of 

 Bremerhaven, and Naval Surgeons Kramer, von Schwab, and Frey- 

 madl. All these observations lead to the same conclusions: The Arctic 

 regions are very rich in summer, while the tropical regions are poor 

 in plankton the whole year round. Conditions specially unfavorable 

 to production appear in the Mediterranean, as in the Saragossa Sea. 

 The single comparison of the curves of volume for the four coast sta- 

 tions where the results have ))een most accurate confirms this conclu- 

 sion. If we take the arithmetical means of the monthly \alues we 

 tind that in New Pomerania the mean volume of plankton for the year 

 is double that at Messina, while for the Kieler Bucht it is ten times 

 that at Messina. 



How shall we explain this remarkable fact, this bizarre contrast 

 between the production of living substances on land and in the sea i 

 First of all. we must get it clearl}- in our minds that the development 

 of plants, and consequently their production, depends not only on the 

 illumination, but also and in quite as large measure on the quantities 

 of nutritive substances that are brought to them. If one of the.se 

 substances, say combined nitrogen, is present only in relatively small 

 amount, the production will suffer from this want. Penury of nitro- 

 gen is suggested, not onh^ by the considerations put forth above, but 

 also in a striking way by the fact that, according to the drafts of 

 plankton, the quantity of nutritive substance in minimum ought to 

 depend very much upon living organisms. Even slight differences of 

 temperature have great importance for the quantity of plankton col- 

 lected, and these differences of temperature affect chiefly the vital 



