VIII 

 DISTRIBUTION OF ALGLE 



THE eastern coast of North America has been divided into 

 four sections, which correspond to the distribution of the 

 alga? which are characteristic of each section. The boundary- 

 lines are not precise, since some species of each section extend 

 beyond the denned limits; but arctic forms are not generally 

 found south of Cape Cod, nor can tropical varieties be expected 

 north of Cape Hatteras. On the intervening coast, however, there 

 are some species common to both sections. The divisions are : 

 (1) Greenland to Cape Cod; (2) Cape Cod to Cape Hatteras; (3) 

 Cape Hatteras to Cape Florida; (4) the Florida Keys and the 

 shores of the Gulf of Mexico. 



On the Pacific coast such distinct lines of demarcation do not 

 exist, there being no such natural barriers as are formed on the 

 eastern coast, first by Cape Cod, and, second, by the stretch of 

 sand-beach which extends from New York to Charleston, and 

 which divides sharply the climatic varieties. 



The whole shore is again divided laterally into three distinct 

 belts, called the littoral, the laminarian, and the coralline zones. 

 The first or littoral zone covers the space between tide-marks. 

 Vegetable life in this zone is subjected first to exposure to the 

 sun and air, and even to desiccation, and then to entire sub- 

 mergence at constantly recurring periods. The rockweeds (Fucus), 

 which are so plentiful in this zone, are very gelatinous, nature 

 having apparently provided the gelatine to protect the cells of 

 the plant from the effects of the alternating extreme conditions. 

 Fucus and Enteromorpha predominate in this zone. 



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