PLATE IV 



{continued) 



Fig. 3. Model representing the wall structure 

 of a Valonia vesicle. The broad lines on the 

 model represent chain directions. Note that 

 one set of chain forms a slow spiral round the 

 vesicle while the other clearly forms meridians 

 radiating from the visible "pole" and closing in 

 again on the basal "pole". 



Fig. 4. X-ray diagram of a bundle of parallel 



filaments of Cladophora sp., beam perpendicular 



to filament length, CuKa radiation. Filament 



length parallel to long edge of page. 



