so 



TEXTBOOK OF BOTANY 



the large seaweeds known as kelps, one of which is the very 

 common rockweed (Fig. 19). A close 

 relative of the rockweed is Sargassum, 

 which is torn by storms from the places 

 where it grows along the American 

 coast, and is carried out into the ocean 

 by currents, especially by the Gulf 

 Stream. Great numbers of the plants 

 come to rest in that part of the north 

 Atlantic which is most free from cur- 

 rents — the so-called " Sargasso Sea." 

 Certain kelps grow to be several 

 hundred feet in length ; they are 

 therefore among the longest of living 

 plants, although of course the bulk of 

 such a plant is not equal to that of 

 a large tree. Kelps have been used 

 for many years as soil fertilizers on 

 the coasts of the Scandinavian coun- 

 tries, the British Isles, France, and 

 New England. Their value for this 

 purpose is due chiefly to the large 

 proportion of potash salts that they 

 contain. Immense beds of kelps exist 

 along the Pacific coast of the United 

 States and Canada, and it is thought 

 that they will prove a most valuable 

 source of potash. Some of the brown 

 algse supply iodine on a commercial 

 scale ; some are sources of mannite. 

 Many brown algse are used for food 

 in China and Japan, on the Pacific 

 islands, and in the Arctic regions. 

 None of the red algse grow to be so 

 large as the great kelps, but many of 



Fig. 19. — The rock- 

 weed (Fncus), a brown 

 alga. At the bottom is 

 an irregularly flattened 

 part that attaches the 

 plant to the rock or other 

 object on which it grows. 

 At various places on the 

 branches are bladder-like 

 swellings which help to 

 buoy the plant in the 

 water. In the swollen 

 portions at the ends of 

 the branches, the repro- 

 ductive structures are 

 produced. 



