140 THE OCEAN 



(1) Chlorophyceae, or green algae ; 



(2) Cyanophyceae, or blue-green algae ; 



(3) Phaeophyceae, or brown algae ; 



(4) Rhodophyceae, or red algae. 



The green and blue-green species live in 

 shallower water than the brown and red 

 species, but blue algae living in deep water 

 may become red, and red algae may become 

 purple, green, or yellow, according to the 

 amount of, and exposure to, sunlight. 



Attached AlgcB. — The attached algae include 

 both brown and red, and are found along 

 practically all coasts, except in polar seas, 

 where the rocks are scoured bare of all life 

 by the grinding action of ice. The brown algae 

 are the commonest and the most characteristic 

 of marine plants, and are sometimes of great 

 size, Macrocystis yiirifera of the Southern 

 Ocean occasionally reaching a length of 700 

 or 800 feet. The common brown algae of the 

 littoral zone belong to the genus Fucus, and 

 immediately below this area at low-water 

 mark the genus Laminaria prevails. Asso- 

 ciated with these plants there is in each case 

 a special and different assemblage of animals. 



The famous Gulf Weed characteristic of the 

 Sargasso Sea in the North Atlantic belongs to 

 the brown algae. It is named Sargassum 

 hacdferuniy and is easily recognised by its 

 small berry-like bladders. This floating weed 



