422 ANNUAL BEPORT SMITHSONIAN INSTITUTION, 1935 



uncovered at ebb and overflowed at flood tide. Fucus natans, appar- 

 ently floating unattached, was described by Columbus as Sargazo. In 

 the North Atlantic, the sailors with Columbus, seeing great olive-col- 

 ored masses of it, thought that it was land. The mariner soon learned 

 that it tails a steady wind, and thus he knew when he found it whether 

 the wind had been blowing in the observed direction for some time. 

 The Sargasso Sea, famous in early explorations, was named from the 

 alga Sargassum, noted for its beauty and grace of form. Its lacelike 

 branches are due to minute species of C ampanularia^ Plumularia, 

 and Sertularia. Sargassum is commonly found in both the Atlantic 

 and the Pacific Oceans, and in tropical and subtropical seas. 



The character of the marine algae is determined by salinity and 

 temperature of the water, light intensity, and the nature of the ocean 

 floor for attachment. The continued existence of the marine algae 

 depends upon their ability to cope with enemies. Their greatest 

 enemy is doubtless the mechanical action of the water during storms, 

 after which the shore is fringed with plants ruthlessly torn from their 

 places. Seaweeds are adapted by structure to yield to or to resist the 

 constant action of the water. Strong holdfasts allow the long and 

 flexible varieties to wave harmlessly back and forth. Stiff, low, and 

 round kinds permit the water to flow over and around them. Prac- 

 tically all seaweeds grow on the sides, upper surfaces, and crevices of 

 large rocks and bedrocks; some grow on stones not longer than 5 

 centimeters, and a few on the under side of stones. 



If sand is shifted in large amounts by water currents, it beats 

 against the algae and buries and kills them. Fishes use seaweed for 

 their food, and this appreciably affects the quantity of some kinds. 

 Many of the larger seaweeds and corallines are protected by secre- 

 tions of lime, but some fishes even eat the corallines. One authority 

 studying Hawaiian fish food found that no fish is strictly herbivorous 

 and the majority are carnivorous. Many eat some algae. The fish 

 were divided into four groups according to their food : Plankton feed- 

 ers, bottom feeders, shrimp feeders, and carnivores. Algae were found 

 in the stomachs of all the groups except the shrimp feeders. 



At times, oceans receive their coloring from the algae that are 

 abundant in their waters at a particular time. Some of the tropical 

 marine forms are phosphorescent. A greenish-brown discoloration 

 of the sand of seashores due to certain species is common after the 

 tide has ebbed. 



SYMBIOTIC AND PARASITIC ALGAE 



Many algae are found living in association with specific plants or 

 animals. A true symbiosis exists when each member of the pair living 

 together contributes to the mutual support. The lichens are the most 



