ECOLOGY AND TAXONOMY OF Holimeda 



39 



mm 



Fig. 18. H. cuneata, longitudinal section, showing parts of two regular segments, a 

 "cushion" segment and a "stalk" region. At the left is the upper portion of a regular 

 segment with part of the cortex included. To the right of it are parts of the small 

 "cushion" segment which is corticated, and the uncorticated stalk region. One or 

 both may be present, and commonly neither occurs. The pattern of medullary 

 filaments at the node, shown at the juncture of regular and cushion segments, is 

 that of fusion in twos and threes, with the participating filaments remaining fused. 

 The entangled condition of the filaments just below the region of fusion adds to the 

 difficulty of nodal dissection. The base of a regular segment, without cortical detail, 

 is shown at the right. (From Hillis, 1959.) 



the broad flat ones of gigas, which may measure to about 31 mm in 

 length and 42 mm in breadth. 



Thickness of segments varies with the number and height of the 

 inner cortical layers, and often decreases from base to apex within a 

 plant. This gradient reflects the relative ages of segments, with older 

 segments towards the base, youngest at the branch tips. Some segments 

 are ribbed, others plane, and the surface of macrophysa and favulosa 

 often appears pitted or stippled because of the large diameters and 

 separateness of their peripheral utricles (Fig. 17, Nos. 16, 24). The 

 species cuneata is unusual in that a small "cushion" segment or an 

 uncorticated "stalk" region, or both, may be interposed between a node 

 and the next regular segment above (Figs 18, 61). 



Colour is influenced by the amount of calcification, proceeding from 

 green to white or yellowish-brown as calcium carbonate increases with 

 age. Young apical segments, therefore, may be a more prominent green 

 than well-developed basal segments (HilHs, 1959). Colour, as a diagnostic 



after the onset of calcification ; (15) H. gigas; (16) H. macrophysa; (17) H. bikinensis, 

 a mature segment: (18) H. bikinensis, a very young segment (green) showing adhesion 

 of utricles at this stage of growth; (19) H. macroloba, mature segment; (20) H. 

 macroloba, young segment; (21) H. incrassata; (22) H. cylindracea, mature segment; 



(23) H. cylindracea, showing somewhat thickened walls of a basal (old) segment; 



(24) H. favulosa; (25) H. stuposa; (26) H. monile; (27) H. simulans. (From Hillis, 

 1959.) 



