CHAPTER IV 

 THE PLANTS 



A. Floating Plants (Phytoplankton). 



BY V. H. BLACKMAN. 



THE marine algae, commonly called "seaweeds/' 

 found growing along the sea-coasts, are from their 

 size the most conspicuous plants of the sea. Apart 

 from these shore algae, which are naturally fixed in 

 position, there are an immense number of plants, 

 practically all of them microscopic, which are found 

 floating free in the sea. 



These floating plants, known as phytoplankton, 

 with very rare exceptions are the only form of veget- 

 able life found over the deeper waters of the ocean, 

 where the " fixed " algae are naturally absent, for, 

 except for accidental floating structures, there is no 

 suitable " hold " other than the sea-bottom. The 

 latter, however, is not available, for the absence of 

 light at any considerable depth precludes the growth 

 of vegetable organisms, for which some degree of 

 illumination is absolutely necessary. 



The phytoplankton is clearly of the greatest im- 

 portance in the general economy of the ocean. In 

 the sea the same rule holds as on land all animal life is 

 dependent, either directly or indirectly, on vegetable 

 life. The vegetable organisms are the only ones 

 whic h are able to obtain nourishment without preying 



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