66 THE WEALTH OF THE SEA 



mately 390 square miles of kelp on the Pacific coast, 

 about half of which was in the vicinity of San Diego. 

 These immense beds seemed to offer an almost in- 

 exhaustible supply of kelp from which the potash 

 requirements of the United States could be met. 

 Later the actual harvesting operations indicated 

 that the amount of kelp commercially available had 

 been greatly overestimated. Around San Diego, how- 

 ever, a great deal of kelp was harvested. In 1918 

 alone, 14,029 tons of potassium salts were produced 

 from this source, and during the war this industry 

 ranked second among the potash industries of the 

 United States. 



The giant kelp called macrocystis is the only im- 

 portant species commercially harvested for its po- 

 tassium content. It grows from a sort of anchorage 

 called a holdfast, sometimes as much as two feet in 

 diameter. A number of stipes (corresponding to the 

 stems of land plants) grow from a single holdfast. 

 These stipes are about half an inch in diameter at 

 the base. They vary from twelve to nearly a hundred 

 in number, and are very long, sometimes reaching a 

 length of a thousand feet. The serrated leaves are 

 about a foot in length and four inches wide. The 

 leaves are held at the surface by a bulb-like float 

 called a pneumatocyst. Since this kelp is a perennial, 

 the beds may be harvested three or four times a year 

 without danger of exhausting them. 



Another kelp called nereocystis often grows 

 around the edge of the beds of macrocystis. This 

 plant consists of a holdfast from which stretches a 

 long stipe that terminates in a nearly spherical float 



