PELAGIC PLANT LIFE 309 



The other expeditions that were sent out about the same 

 time as the "Challenger" carried out their investigations on 

 similar lines. G. O. Sars, who was a member of the Norwegian g. o. Sars. 

 North Atlantic Expedition in 1 876-1 878, made a study on 

 board ship of the luxuriant plant life near the ice-limit, and re- 

 marked, like QErsted before him, that plants are really the basis CErsted. 

 upon which the nutriment of animals is founded. It was not, 

 however, till twenty years afterwards that an examination was 

 made of the algae in the comparatively small number of samples 

 then collected. 



Soon after 1880 Hensen commenced a physiological study Hensen. 

 of the sea, and essayed principally to estimate its production of 

 nutritive substances at different seasons. As a result the plants 

 came more into notice than they had previously done ; and it is 

 significant that Hensen found it necessary to introduce the new 

 name of " plankton " to designate generally all pelagic organisms, "Plankton 

 both plants and animals, regarded as one universal community. 

 The term "plankton" is now used for all floating organisms 

 which are passively carried along by currents, while "nekton" "Nekton." 

 — a term introduced by Haeckel — is used to designate all 

 pelagic animals which are able to swim against currents. 

 During Hensen's Plankton Expedition in 1889 Schlitt made Schutt. 

 the first investigations regarding the general biology of the 

 plankton - algse. His ingenious descriptions and admirable 

 drawings explained the different ways in which the alga; adapt 

 themselves to their floating existence. 



An endeavour was made by Hensen to find a method of Qu; 

 calculating the quantity of pelagic organisms occurring in 

 different localities. He constructed nets to be drawn up for 

 certain distances through the water, that were supposed to 

 filter the whole column of liquid through which they passed, and 

 to retain all the organisms existing therein. The total amount of 

 these organisms was then measured by determining the volume, 

 and a most careful enumeration was made of the number 

 of individuals belonging to each species. The nets were drawn 

 vertically through the whole zone where plant plankton is abund- 

 ant, that is to say, from a depth of 200 metres to the surface ; 

 and Hensen attempted to utilise the results for measuring the 

 production of life in a column of water whose superficial area is 

 one square metre. He tried at the same time to solve import- 

 ant problems, such as the rate of augmentation of algse, or what 

 proportion of individuals disappears owing either to consump- 

 tion by other organisms or unfavourable conditions of existence. 



uantitative 

 estimations. 



