., •■ 



L^ 



COD FISH. 



CHAPTER V 



The Fishes of the Northern Seas 



The animal-life of the sea, like that of the land, depends largely on the nature of 

 the local plant-life. Marine plants in the main belong to groups entirely different 

 from all land or even fresh-water vegetation, although the marine flora is connected 

 with that of fresh water by means of the brackish-water flora, which, however, is 

 of very limited extent. Apart from the essential difference between marine and 

 fresh-water vegetation, the local variations in aquatic floras, due to climatic con- 

 ditions, are much less marked than are those of land floras, owing to the more 

 equable temperature of water. Although in the sea the influence of warm and cold 

 currents has to be largely taken into account, while in fresh water the amount of 

 rainfall is an important factor, yet the depth of the water is all-important in regard 

 to plant life. In addition, the amount of light received exercises a most im- 

 portant influence, the larger plants growing only near the surface, where the light 

 is brightest, while the smaller and most lowly organised types alone inhabit the 

 darkest depths. Moreover, the water has not only what may be called its basal 

 flora, but likewise supports a vast development of plant-life which floats on its 

 surface, this floating flora only being fully developed where the water is of great 

 depth, although in the shallows on coasts and elsewhere it may be mingled with 

 the basal flora. 



The nature of aquatic floras depends much on that of the river or sea bottom, 

 whether this be rocky, pebbly, muddy, or sand}*. The basal flora in fresh water 

 consists chiefly of such plants as thrive in mud, while that of the ocean is largely 



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