DISTRIBUTION OF THE ALGjE. 229 



iu the sea ? Modern botanists have proved, experi- 

 mentally, that plants are very sensible to the action 

 of light, and it has been found that marine plants 

 are of different colours, according to the depth at 

 which they grow. 



They have been divided, according to their pre- 

 vailing tint, into three main sections : the brown or 

 black (melanospermea), the green {chloros;perniea), and 

 the red (rhodoaperniea). The green live only near 

 the surface ; they often float, and are found in large 

 quantities in the grassy seas. The red are found at 

 small depths on rocks near the coasts. The brown, 

 which are much more numerous, grow at greater 

 depths. They constitute the greater part of the 

 submarine forests. 



Although the alga3 occupy, relatively, but a small 

 portion of the earth's surface, being distributed in 

 what may be called oceanic belts, their number is 

 immense. Wherever the physical conditions are 

 favourable to their development, they fill the sea 

 with their impenetrable masses. This abundant 

 vegetation is utilised by man, whom the sea itself 

 aids in collecting them. Wind-storms sometimes 

 produce terrible effects, but oceanic storms far 

 exceed them in destructive force. If the first over- 

 throw enormous trees or immense edifices, the latter 

 easily tear whole forests of marine plants fiom theii* 



