THE LAW OF THE MINIMUM IN THE SEA 193 



what is the average number of eggs spawned by a mature 

 female fish, and thus the number of the latter which had 

 spawned the eggs counted could be calculated. Now these 

 were the primary objects of the Scandinavian and German 

 plankton investigations, but as the methods elaborated for the 

 solution of the problems were developed other questions of 

 more theoretical interest became studied, and it is some of these 

 which I propose to discuss. 



In 1889 the first expedition which had for its primary object 

 the study of the plankton of a large sea area was organised. 

 In that year the National left Kiel for a four months' cruise in 

 the Atlantic Ocean. In the course of this famous voyage five 

 traverses of the North Atlantic were made, and quantitative 

 and qualitative plankton collections were obtained from about 

 four hundred stations on these lines. An enormous bulk of 

 material was thus collected, and as the most of this had to 

 be quantitatively examined it is the case that the complete 

 results of the Plankton Expedition are not yet published. 

 Nevertheless, many of the groups of organisms collected are 

 already described, and notable additions to our knowledge of 

 species and of limits of distribution have been made. The 

 first solid contribution to our knowledge of the bacterial flora 

 of the sea, for instance, is contained in the Ergebnisse of the 

 Plankton Expedition. 1 The main interest of the voyage, from 

 our present point of view, is that it for the first time directed 

 attention to the cause of the astonishing contrast which has 

 been observed in the distribution of life on the surface of the 

 land and in the sea. The examination of the material collected 

 by the National showed that the plankton of the colder parts 

 of the area investigated was everywhere more abundant than 

 in the warmer sea areas traversed. 



There is such a profound difference between the distribution 

 of life on the land and in the sea that one fails at first to be 

 convinced of the accuracy of this result of the Plankton 

 Expedition. Everywhere on the land both vegetable and 

 animal life is most abundant in the tropics and decreases as 

 we pass from the equator to the poles. " He who," says Brandt, 

 " has been compelled to force his way through a tropical 

 forest and then sees the stunted vegetation of Spitzbergen just 



1 Fischer, " Bakterien des Meeres," Ergebti. Plankt.-Exped, Bd. 4, Kiel u. Leip- 

 zig, 1894. 



