CARBOHYDRATES, CHITIN AND CUTIN 



3^5 



Fig. i6i. Diagram of the submicro- 

 scopic structure of a layer of a starch 

 grain, a Outer portion looser, less 

 refractive, with little interlinking; / 

 inner portion denser, more refractive, 

 more closely interlinked. 



The stage of voluntary spherite formation is comparable to the 

 structure of starch grains. The starch molecules are obviously also fixed 

 in a radial direction by water of hydration. In this case, however, 

 the water does not function as a solvent, but participates, as a loosely 

 bound constituent, in the build-up of the spatial lattice. The starch 

 chains are far more highly polymeric 

 than the molecules of konyak mannans . 

 Notwithstanding this, the amy loses 

 are soluble and, if the starch grain 

 seems nevertheless to swell only to a 

 limited degree, there must be some 

 particular hindrance to solution. This 

 is probably to be found in the amylo- 

 pectin, the glucosan chains of which 

 are interlinked. There is good reason 

 to believe that these amylopectinous 

 linkages occur in each individual layer 

 of the starch grains in the inner, denser 



and more refractive portions and that independent, amylose chains 

 are accumulated in the outer, looser portions of the layers. Jaloveczky 

 (1942) states that the lamellae containing amvlopectin are isotropic, 

 whereas those containing amylose are anisotropic and can be stained. 



It has been suggested that all the amylopectin is localized in the 

 outermost marginal layer of starch grains, which is resistant when they 

 are made into paste. It would seem more probable, however, that the 

 starch is liable to every conceivable transition from the easily soluble 

 amyloses to the virtually insoluble constituent of the amylopectin, 

 which resists even enzymatic degradation. Thus it might be supposed 

 that amylopectins occur in the denser portions of all the layers, though 

 not in the same degree as in the insoluble outside layer which resists 

 when starch is made into paste. On this assumption the submicro- 

 scopic structure of a starch grain layer was represented in 1938 as in 

 Fig. 161. 



This diagram takes into account the following observed facts : The 

 density and refractive index at the core of a layer diminish gradually 

 towards the outer regions and then increase suddenly at the boundary 

 of the layer. The solubilitv is not equal everywhere within the layer. 

 The water of constitution between the chains is partially bound as 



