THE ALGJE 



135 



Color. The characteristic red color is due to the presence of a 

 red pigment, Phycoerythrin, which occurs in the chromatophores 

 with the chlorophyll. This 

 pigment is soluble in fresh 

 water, and forms a rose-red 

 solution which is strongly 

 fluorescent, appearing green- 

 ish yellow by reflected 

 light. The pigment varies 

 in amount, being least de- 

 veloped in the fresh-water 

 species, which are generally 

 blackish or olive-green, re- 

 sembling in color the Cyano- 

 phyceae. The marine species 

 exhibit all shades from 

 delicate rose-red to blackish 

 purple. 



Chromatophores. The 

 chromatophores, except in 

 the Bangiaceae, which are 

 not closely related to the 

 other forms, are usually 

 small, oval disks, several in 

 each cell. Just what the 

 relation of the phycoerythrin 

 is to the chlorophyll is not FIG. 105. Dictyota dichotoma: a, female 



quite clear, but it is evident "f^ ; b ' m le ^TJ* ' porangi ^ (A11 

 A , ., ,, ,. , highly magnified.) (After MURRAY.) 



that it modifies the light- 

 rays, as it is found by experiment that the rays most efficient in 

 photosynthesis are noticeably nearer the violet end of the spectrum 

 in the Rhodophycese than they are in the Chlorophyceae. The 

 phycoerythrin no doubt neutralizes the absorption of certain rays 

 in the passage of light through the water, where these plants grow 

 in deep water. 



Plant-body. Some of the Rhodophycese are simple filaments 

 (Griffithsia), or branched filaments, as in Callithamnion. A thin, 

 flat thai 1 us is found in Grinnellia and Porphyra, while some of the 

 forms living where they are exposed to the surf, such as Chondrus 

 or Gigartina, are tough and leathery in texture like some of the 

 Kelps. Much more rarely there is an incrustation of lime, and 

 the plants become of stony hardness. This occurs in the peculiar 

 Corallines. 



Cell-structure. With the exception of the Bangiales, which are some- 

 times removed from the Rhodophycese, the protoplasts of adjacent 



