INTERCELLULAR SUBSTANCES AND WALLS 



83 



traces of arabinose. Some Chlorella species contain a hemicellu- 

 lose composed of glucose. 



Table 5. A Composite Summary of Algal Wall Substances 



Some chlorophycean cell walls consist of a single cellulosic 

 layer (Protococcus) but a multilayered condition is more common 

 (Table 6). The walls of Oedogonium and Cladophora consist of an 

 inner cellulosic layer, a pectic middle layer and a chitinous outer 

 layer; Mesotaenium and Chlamydomonas contain only inner cel- 

 lulosic and outer pectic regions; Oedogonium contains an inner 

 cellulose layer, a central layer of cellulose (thin) and pectin (thick), 

 and an outer pectic layer. 



The organization of cellulose in the cell wall of Valonia (Si- 

 phonocladiales) has been examined by x-ray and electron micro- 

 scopic procedures. The wall contains several dozen lamellae, each 

 in turn an array of parallel fibers. In successive lamellae, the fibre 

 orientation alternates so that an extensively crossed structure 

 results. The cellulose fibrils are about 300 A in diameter and 

 extremely long (10[jl or more). In Cladophora (Cladophorales) the 

 chains in successive lamellae make an angle of 83° with one another. 

 The alternation further consists of steep and flat spirals. 



In the Pyrrophyta, the cellulosic wall is commonplace; some 

 dino flagellates (Dinophyceae), have non-cellulosic walls; most 

 motile forms have heavy homogeneous walls composed of inter- 

 locking cellulose plates; non-motile dinophyceans also possess 

 pectin sheaths. The Chrysophyta contain three classes and a dozen 



