CARBOHYDRATES, CHITIN AND CUTIN 



325 



XXIX, p, 5 1 2), the arrangement of the amylopectins is more important, 

 b) and c) show such molecules of n '-^ 8000 and n -^ 2,000,000; it is 

 remarkable that a dichotomous amylopectin molecule of n ~' 2,000,000 

 should have only the same length {ca. 0.09 ;*) as an amylose molecule 

 of n/--' 250. The many end members of the amylopectin molecule are 



Fig. 163. Interpenetration of amylopectin chains of opposite orientation (from Frey- 

 Wyssling, 1948 c). Arrows indicate the non-reducing end of the chains. Dotted areas 



= crystalline regions (cf. Fig. iGzf). 



not aldehyde in character; only the glucose residue at the starting 

 point of the bifurcated high polymer has an open aldehyde group. 

 Therefore, it is likely that such a molecule grows by adding new 

 glucose molecules with the active aldehyde group to the brush end. 

 This is the reason why in Fig. 162 the molecules have been oriented 

 in such a way that their growth direction coincides with that of the 

 apposition growth of the starch grain. Since the amylopectin is 

 attacked by the /5-amylase from the non-aldehydic end, this would 

 explain why the enzymatic dissolution of the starch grain often starts 

 at the outer boundary of its layers. However, such an arrangement 

 would cause a higher density of the layer in its outer portion as seen 



