THE BROWN ALG^E 205 



CLASS III. THE BROWN ALGLE, OR PH^OPHYCE^E 



233. The brown algae. The Pliceopliycece comprise a very 

 large assemblage of marine algae, or seaweeds, called the brown 

 algae because their chromatophores are colored brown instead of 

 green. The brown pigment, however, performs the same sort 

 of work (photosynthesis) as the chlorophyll of the green algae. 

 The brown algae can generally be recognized at a glance by 

 their color, but the group is really separated from all other 

 classes of algae by certain peculiarities of structure, or mor- 

 phology. The plant bodies in most of the forms are very much 

 larger and more complex than those of any green algae and fre- 

 quently have a degree of differentiation quite above that of the 

 typical thallus. Indeed, some of the higher brown algae have 

 well-defined stems fastened to the rocks by remarkable hold- 

 fasts, resembling clusters of roots, and bearing expanded leaf- 

 like structures of complex and striking forms. Certain types 

 develop swollen bladders, which contain considerable oxygen, 

 given off from the tissues, and serve to float parts of the plant 

 in the water. Besides the complexity of the plant body the 

 brown algae are also distinguished by peculiarities of the repro- 

 ductive organs that can only be understood through a study 

 of types. Iodine is obtained from the ash of certain kelps and 

 rockweeds. These larger brown algae are also gathered from 

 the rocks and beaches by the peasantry of certain European 

 countries and by farmers on the New England coast and spread 

 over farm lands to fertilize the soil. 



234. Life habits. The brown algae are most luxuriant in the 

 colder waters of the oceans, where they form extensive growths 

 along the coasts. Some of the larger forms, as Fucus and 

 Ascophyllum, are known as rockweeds because they cover the 

 rocks between low and high tide marks with heavy fringes of 

 brown vegetation (Plate IV). Other forms, known as the kelps, 

 or devil's aprons, grow below or just at low watermark and some- 

 times form large beds attached to the rocks. These larger types 



