12 



L. HILLIS-COLINVAUX 



(Borowitzka and Larkum, 1977), is most readily observed in young 

 segments and often is obscured by calcium carbonate crystals. 



C. Inside the filament 



The filament wall bounds the cytoplasm. The organelles are not uni- 

 formly distributed throughout the cytoplasm although the construction 



Fig. 10. H. nionile. Section of a filament from a segment less than 48 hours old showing 

 wall with fine fibrils on outer surface, two nuclei (n), chloroplasts (c), plastid with 

 concentric lamellae and starch grain (upper right-hand corner), chloroplast with 

 small starch grain (below the nuclei), mitochondria (m) and electron-dense bodies (e). 

 Calcification has begun m the spaces outside the filaments. The white spaces near 

 the filament wall represent the location of crystals that were lost in the sectioning 

 process. Stained with lead tartrate. Scale bar is 1 [xm. 



