CHAPTER VI 



PELAGIC PLANT LIFE 



Not many years have elapsed since the scientific world became Historical 

 aware that the sea contains plants in abundance floating on and introduction. 

 beneath its surface, and that they build up the organic sub- 

 stances upon which marine animals depend. In the open sea 

 the plants are too minute to be detected without the microscope ; 

 so that, until this instrument came to be regularly employed by 

 biologists, it was impossible to know anything about them. 



The first to use the microscope for studying unicellular 

 organisms in the sea was the celebrated Danish zoologist, 

 O. F. Mtiller, who, in 1777, described one of the most important o. f. Muiier. 

 plants of our northern waters, namely, Ceratimn tripos. He 

 was succeeded by the microscopist Ehrenberg, who laid the Ehrenberg. 

 foundation of our knowledge regarding the multiplicity of forms, 

 their wide distribution, and their significance in the economy of 

 nature ; and also discovered the coverings of diatoms together 

 with coccoliths and the skeletons of various unicellular animals 

 (radiolaria, foraminifera) in deposits on the sea-bottom and in 

 geological strata from previous ages. Ehrenberg aroused 

 interest by pointing out the wonderful structure of these 

 coverings, and improvements in the microscope have resulted 

 in fresh wonders being disclosed, which have induced quite a 

 number of capable amateurs to take up the study of diatoms. 



Classification of these algae dates from about the middle of the 

 nineteenth century. It is based on the shape and structure of the 

 cell-wall, less attention having been given to the living contents 

 and to the biology. The pelagic forms have as a rule thinner 

 coverings, and a more indistinct structure, than the robust species 

 nearer the coast, and have therefore been less studied. How- 

 ever, occasional samples have now and then been collected from 

 the surface with nets, and researches have been carried out by Bailey. 

 J. W. Bailey in the waters off Kamchatka, by Brightwell along Brightwdi. 



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