ECOLOGY AND TAXONOMY OF Holimeda 



185 



Fig. 56. H. 7nonile. Cross-section of a filament from an old, white suprabasal segment, 

 showing the much thickened wall of some of the filaments, spherical body (s), and 

 aragonite crystals filling the segment space. The density of cytoiDlasmic organelles 

 appears to be comparatively low in old, white, heavily calcified segments. A jDortion 

 of a filament with wall of more usual thickness appears on right-hand side. Stained 

 with lead tartrate. Scale bar is 0-1 [i.m. 



3. Old basal segments 



In these segments, which occur mostly on perennating thalli or old 

 thalU, the filament wall may be considerably thickened, up to at least 

 2 [Jim, and stratified (Fig. 56), although there is also local thickenmg in 

 younger material. Amyloplasts are relatively prominent m some of the 

 material as are spherical bodies (Wilbur et al., 1969). 



4. Wounding response 



Siphonaceous algae, when wounded, quickly produce a yellowish 

 material often referred to as a callose or mucilagenous substance 



