212 L. HrLLIS-COLESrVAUX 



B. Vegetative reproduction of Halimeda 



Halimeda plants that grow in sand reproduce by "runners" of 

 filaments (Fig. 69). These filaments, or bundles of filaments, are at least 

 20 cm long (the limits of my aquaria) and spread laterally through the 

 substrate from the main holdfast (Colinvaux et al., 1965; Colinvaux, 

 1968a, b; Hillis-Colinvaux, 1972, 1973). They are non-photosynthetic, 



Fig. 69. Vegetative reproduction in Halimeda by "runners". A fine, filamentous thread 

 or collection of such threads coiuiects the rhizoidal portions of four young Haliniedae 

 which developed in an aquarium. See also Fig. 46. (Photograph by The Ohio State 

 University Department of Photography.) 



and are individually fine and threadlike. The walls of the filaments are 

 relatively thick, and in places pigmented yellow and regularly con- 

 stricted, so that the thread sometimes appears like a string of beads, 

 particularly in the immediate vicinity of the plant. Eventually they 

 produce a tight clump or cone-like mass of filamentous material (Fig. 

 70) which pushes up out of the substrate and from which the Halimeda 

 segment is organized (Section VI). More segments are produced, some- 

 times at the rate of at least one a day per growing tip (Colinvaux et al., 

 1965). Eventually the physical connections between young and parent 

 thallus are lost. 



