CH. X] THE RED ALG^B 445 



much eaten in Japan, and invaluable in bacteriology as a 

 culture basis for Bacteria. The distinctive rose-red color 

 is given by a special pigment, called PHYCOERYTHRIN, present 

 in the chromatophores with the chlorophyll. It appears to 

 aid in photosynthesis, though the method is not wholly 

 clear. Perhaps it works through its fluorescence, by which 

 rays of light otherwise unavailable are brought within reach 

 of the chlorophyll, all possible rays being valuable where 

 so many are lost through absorption by the water. Some 

 kinds have the power, in common with other Algae (Charales, 

 Acetabularia) , to store up lime in their walls; and thereby 

 they add irregular stony growths to the rocks upon which 

 they grow. Such is the nature of the pink "nullipores" 

 found at extreme low tides on our own coasts and often mis- 

 taken for coral, while in the tropics they actually contribute 

 largely to the construction of the real coral reefs. They 

 reproduce asexually by non-motile drifting spores, especially 

 a characteristic kind formed in groups of four and called 

 TETRASPORES (Fig. 311). No motile reproductive bodies of 

 any kind are found in the group. Their sexual reproduction, 

 however, is elaborately specialized, as noted below. 



The Rhodophycese include three or four orders, of which 

 a single one, the Floridece, is so much the larger and more 

 important as to become almost synonymous with the class. 

 One of the commonest and simplest in reproduction of 

 the Floridese is Nemalion, a small, branching, filamentous, 

 purplish form which grows in patches on rocks among the 

 Rockweeds. Its only known method of reproduction is that 

 ^partially represented in Figure 217. The combir^d egg nell 

 (CARPOGONIUM) and trichogyne there shown is called a 

 PROQARJP; after fertilization, effected by the small, round, 

 non-motile sperm cell (SPERMATIUM) , the trichogyne withers, 

 and the egg cell grows into a compact, branched structure^ 

 producing asexual spores on the branches, the entirejnass 

 being called a CYSTOCARp.The spores grow each to a new_ 

 plant. A practically similar method of reproduction occurs in 



