88 THE PLANT CELL WALL 



ness, and possess considerable area relative to mass. The crystals 

 lie in the ground substance, forming a periodic pattern around the 

 collagen fibers in a definite relation to the 640 A period. 

 Mineralization is believed to occur as a catalyzed crystallization 

 involving nucleation centers within the matrix. 



Hydroxyapatite is a mineral commonly identified with the 

 osteogenic activities of the vertebrates. It is part of the intercellular 

 organo-mineral complex involved in bone formation. In the cyto- 

 plasm of the ciliate, Spirostomum ambiguum, which has been 

 extensively studied because of its size and ready cultivation, calca- 

 reous particles of 0.5-3[jl diameter have been observed in all but 

 the most youthful, dividing stages. By X-ray diffraction these 

 bodies, which possess considerable fine structure, were shown 

 to consist of hydroxyapatite. The fundamental crystallite resembles 

 in size the primary particles in bone. It is claimed that the mineral 

 particles are deposited on and/or within a fibrillar nucleus, revea- 

 ling thus a relationship similar to that in bone. 



A Note on Antigenic Cell Wall and Related Polysaccharides 



It is well known that polysaccharides determine the immunolo- 

 gical specificities of many micro-organisms, but it has been recog- 

 nized only recently that the polysaccharides of many plants and 

 animals may also react with antibodies evoked in experimental 

 animals by suitable bacterial antigens. 



Even with the limited experimental data now available it is 

 abundantly clear that wall polysaccharides of the vascular plant 

 are able to precipitate the antisera formed in the presence of the 

 capsular polysaccharides of several pneumococcal types (Table 7). 



In addition to the several cell wall polysaccharides noted, 

 types II and XIV antigens evoke antisera precipitated by synthetic 

 polyglucoses. 



In addition, almost all pneumococcus antisera are precipitated 

 by agar, carragheenins, and other polysaccharide sulfates. 



Aside from its direct immunological interests, the immuno- 

 chemistry of cell wall polysaccharide components offers a valuable 

 tool in the study of their biological and molecular properties and 

 specificities. 



