PLANT LIFE 139 



common along the coasts of the Atlantic in 

 sheltered localities with a soft muddy bottom, 

 and in such positions this plant provides 

 shelter for some distinct and characteristic 

 species of animals, which live mainly, perhaps 

 exclusively, in its vicinity. 



The vast majority of sea-plants belong, 

 however, to the algae. Owing to the vertical 

 direction of the sun's rays and their consequent 

 greater penetration in the tropics, algae are 

 found at a greater depth towards the equatorial 

 regions than towards the poles. They differ 

 from terrestrial plants in finding their nourish- 

 ment dissolved in sea-water, and this being 

 uniformly distributed around them they can 

 take in food throughout the entire surface of 

 the organism. They all possess green chloro- 

 phyll — that magician which, conjuring with 

 the sunbeams, is able to build up organic 

 compounds from inorganic constituents. The 

 green chlorophyll is often masked by other 

 pigments of a red, brown, blue, or yellow 

 colour. 



The algae may be divided according to 

 habit into two main groups : (1) those attached 

 to the bottom (Benthos), and (2) those which 

 pass their whole life-cycle floating in the 

 water (Phytoplankton), and in accordance 

 with their predominant colouring they have 

 been arranged in four groups : — 



