42 HABITS OF SEA-WEEDS. 



fields of it are seen by the navigator, extending as far as the eye 

 can reach, and conveying the idea of rocks and shallows. 

 dangers far distant. It is sometimes so abundant, as seriously 

 to interfere with the progress of the ship through the water ; and 

 it was this which alarmed the crew of Columbus, in his first 

 voyage of discovery. 



44. The distribution of different species through the ocean, is 

 influenced by latitude, by the depth of water, and by currents, 

 nearly in the same manner as the higher plants are affected by 

 temperature, elevation above the sea level, and the conditions of 

 the atmosphere as to dryness and calmness. Some species can 

 thrive well under considerable variation in these conditions ; 

 whilst others are dependent upon certain states of them for their 

 existence. The former, therefore, are extensively diffused, being 

 found along many shores, whilst the latter are rarer, and only 

 inhabit particular spots, in which these conditions are met with. 

 Contrary to what might have been expected, considering that 

 the Algae do not imbibe any nourishment by the spreading root- 

 like fibres, which attach them to the solid masses of the shore, 

 it has been ascertained that they do not grow indifferently on all 

 kinds of rocks ; but that if, for example, along the same line of 

 coast, there be an alternation of limestone and granite rocks, 

 some species will attach themselves in preference to the former, 

 and others to the latter. This curious fact can only be explained 

 by the supposition, that small quantities of the mineral matter 

 are dissolved by the water of the neighbourhood ; and that in 

 this manner they act upon the plant. 



45. Of all tribes of plants, the Algas are commonly reputed 

 the least useful ; in fact their inutility was proverbial among 

 the ancients. Yet neither in regard to the general economy of 

 nature, nor as to the wants of man, are they to be so considered. 

 They supply food to a large number of marine animals, which 

 browse upon them as those inhabiting the land do upon its most 

 luxuriant pastures. Cattle have been very profitably fed on 

 some species abundant on the northern shores ; and even become 

 so fond of this diet as greedily to seek for it. Many kinds, 

 such as the Alaria esculenta, called in Scotland badder-locks or 

 honev-ware, furnish a wholesome and palatable food for Man, 



