ECOLOGY AND TAXONOMY OF Holimeda 



201 



Fig. 62b. Same plant shown in Fig. 62a, in culture, five weeks later, showing complete 

 disintegration of the thallus. In the reef the thallus would have collapsed sooner 

 from currents and animal disturbances. Scale bar is 1 cm. 



inference. That the flagellated zooids were evidence of a sexual cycle 

 was not finally demonstrated until fusion was observed in remarkably 

 recent times (Nasr, 1947; Chihara, 1956; Kamura, 1966; Merten, 1971; 

 Meinesz, 1972b). 



The demonstration of vegetative reproductive cycles in Halimeda 

 has been even more recent. Field workers have long noticed that some 

 sort of reproduction by creeping growth through sand must occur, but 

 only recent culture work has shown the details and varieties of this 

 process (Colinvaux et al., 1965; Colinvaux, 1968b; Hillis-Colinvaux, 

 1973). This work shows that individual Halimeda thalli have a definite 

 term to their existence, and that new thalli are cloned from creeping 

 rhizoids of the parent thallus, or from broken portions partially buried 

 by chance. There is no difficulty in recognizing generations in Halimeda 

 (Fig. 63), whether these be sexual or asexual, and the life-cycle always 

 seems to involve youth, a maturity measured in months, sometimes 

 longer, senescence and death. 



