82 THE PLANT CELL WALL 



both containing mannose and glucose in the ratio of 2:1. The 

 hexosamine corresponds to a chitin content of about 3 per cent. 

 Lipid content totals about 8 per cent and is principally in a bound 

 form; protein content totals about 7 per cent distributed among 

 the polysaccharides as discussed. The protein component is of 

 special interest, as it contains an exceptionally high (2 per cent) 

 sulfur content. The sulfur in this pseudokeratinous protein which 

 we have seen is intimately associated with polysaccharides, is 

 critically involved in cell division in yeasts, illustrating the iden- 

 tity which may be attained by architectural and functional units 

 in the operation of life processes. 



It is apparent that a phycomycete can contain chitin whereas 

 an ascomycete can possess great amounts of hexoses and little 

 chitin. The cell walls of other phycomycetes, Rhizopus and Mucor, 

 contain only glucosamine units, whereas the cell wall polymers 

 of the Aspergillacese (ascomycetes) contain galactose, glucose, 

 and mannose in addition to glucosamine. 



The class Myxomycetae (phylum Myxothallophyta), also 

 recognized as the protozoan order Mycetozoa (class Sarcodina), 

 consists of organisms which exist for the greater part of their life 

 cycle in naked protoplasmic form. Formation of cellulosic or 

 calcified cellulosic walls is associated with sporulation and with 

 resting or sclerotial stages, which form under unfavorable envi- 

 ronmental conditions. 



Algae and Selected Protozoa 



The biochemical and morphological diversity known in the 

 algae applies to their cell wall chemistry, however, save for the 

 Chrysophyta (Chrysomonads, diatoms) cellulose is a typical wall 

 component in all phyla (Table 5). In the Chlorophyta, cellulose 

 may be accompanied by polysaccharides containing galactose and 

 glucose (Spirogyra); by polyuronic acids such as pectin (typical of 

 the Chlorophyta in general); or by chitin (Cladophorales, Oedogo- 

 niales). On the other hand, volvocalian forms such as Haematococcus 

 and Platymonas and chlorococcalian forms such as Ankistwdesmis, 

 Chlorella and Scenedesmus contain little or no cellulose. The 

 Platymonas wall contains galactose and uronic acid units, and 



