214 



THE ALG^E 



and performs the photosynthetic work of the plant. Although 

 the red algae can generally be distinguished by their color, 

 the fundamental characters of the group are based on the 

 structure of the sexual organs and certain complications in 

 the life histories which will be explained in the accounts of 

 Nemalion and Polysiplionia. The plant body of the red algaa 



ranges from filamentous types 

 of great delicacy (as Callitliam- 

 nion) to such coarse forms as 

 the Irish moss (Chondrus) and 

 the dulse (Rhodymenia). It is a 

 remarkable fact that the large 

 types are really composed of 

 complicated systems of filaments 

 so closely associated, however, 

 as to give the appearance of a 

 cell tissue. Adjacent cells in 

 the same filament are usually 

 connected by strands of proto- 

 plasm, a striking feature of the 



group. Some of the red alga?, 

 FIG. 201. The Irish moss (Chondrus as the Irigh mogs and the dulsej 



are eaten, and a number of them 



About one half natural size; the shaded , ,. , 1,1 



spots are sexually formed fruits, or are used as relishes by the na- 

 cystocarps tives of the Hawaiian Islands, 



China, and Japan. Certain forms have an economic value for 

 gelatin, which is obtained from their tissues ; thus agar-agar 

 comes from the stems of a red alga (Gracilaria) which grows 

 in the seas of the Orient. 



241. Life habits. The life habits of the red algae are in strik- 

 ing contrast to those of the brown. They prefer warmer waters, 

 and the best displays are on such coasts as the Mediterranean, 

 the islands of the West Indies, southern California, and Aus- 

 tralia, They generally nourish in deeper waters than the green 

 and brown algae, and form the greater part of the seaweed growth 



