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354 PHARMACEUTICAL BOTANY 
by the Devil’s Aprons or Laminaria and the Sea Palms (Postelsia) 
which grow on rocks along the North Atlantic coast and by the 
giant kelps Macrocystis (Fig. 258) and Nereocystis (Sea Otter’s 
Cabbage) found along the Pacific coast of the United States. 
Laminaria digitata is an abundant kelp off the coast of New 
England where it grows attached to rocks by a holdfast consisting 
of a whorl of rootlet-like structures. From this arises a solid 
cylindrical stipe bearing on its end an oval or lance-shaped 
Fic. 258.—A giant Kelp (Macrocystis), one of the Brown Algz. (From U.S.D.A. 
Bur, Soils.) 
blade, the latter becoming split into finger-like segments at its 
summit. Postelsia or the Sea Palm has a holdfast of several — 
whorls of stubby rootlet-like structures and a rigid stipe about a 
foot in length, the latter terminating in a number of lanceolate 
blades. 
Because of their rich content of potassium salts, the kelps are 
used extensively as fertilizer. They also contain a fair amount of 
iodine and represent one of the chief sources of this drug. 
Tue Rockweeps.—To this group (Order Fucales) belong the 
brown seaweeds which cover many of the rocks along our North 
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