HOW TO KNOW THE SEAWEEDS 



Unlike the vegetation of the surface water masses of the oceans, 

 that of the illuminated sea floor and of the shore consists mostly of 

 readily visible plants of which some reach large size. Among these, to 



be sure, there are mtiny 

 microscopic forms, includ- 

 ing littoral diatoms (Fig. 

 4) and minute blue-green 

 algae (Fig. 5) which some- 

 times form more or less 

 conspicuous macroscopic 

 colonies. These must be/ 

 neglected here, however, 

 in favor of the three main 

 groups of seaweeds with 

 which we need be con- 

 cerned, namely, the Green 

 Algae (Chlorophyta), the 

 Brown Algae (Phaeophy- 

 ta) and the Red Algae 

 (Rhodophyta). The seed 

 plants, although of very 

 few kinds, are exceeding- 

 ly abundant in many 

 coastal habitats and will 

 be accounted for and il- 



Fig. 4. Two examples of different forms of Instrated at the end of 



littoral diatoms. lusiiaiea ui iiit? eiiu ui 



A. An epiphytic, chain form, Grammatophora. thiS book. 

 B. A stalked form, Licmophora. 



These three groups of algae which make up the vast majority of 

 the seaweeds are named because of the predominant colors which 

 their members commonly assume, and are technically distinguished 

 by the chemistry of their pigments. Thus, the Green Algae are char- 

 acteristically pigmented only by green chlorophyll, while the Brown 

 and Red Algae have their chlorophyll masked by other pigments. On 

 this account the Green Algae almost always appear green in color, 

 while the others may be neither brown nor red, depending upon the 

 relative dominance of the chlorophyll or of the masking pigments. 

 When the color is such as to leave one in doubt as to the group to 

 which a plant may belong, other characters must be taken into ac- 

 count in identification. Because of the difficulty experienced by most 

 students in recognizing according to color the main group to which 

 a seaweed belongs, the present key treats all of the Green, Brown 



