STARCH-SUBSTANCE, AND THE STRUCTURE, ETC., OF THE STARCH-GRAIN. 



57 



staining reactions with canna starch are summarized by Denniston in tables 1 and 2, the 

 order of the pai'ts being from the margin inward. 



Table 1. 



Table 2. 



The layers which take the deepest color with iodine and gentian violet Denniston 

 regards as being the more dense, but, in case of such precipitants as were used by Meyer 

 {loc. ciL, p. 51) and Fischer {loc. cit., p. 55), the less dense. The liinitation of the orange 

 layer, he holds, can not be due to hindi'ance to the penetration of the dye, because the layer 

 does not become thicker in time and because in the case of crushed grains in which the dye 

 has access at once to all of the layers the parts adjacent to the outer layer do not become 

 yellow. He also noted that the central part of Canna grains stain yellow, and that frequently 

 young grains stain entirely orange with the exception of one or two dots, thus in agreement 

 with the view expressed by others that the young grain is of difTerent composition from the 

 later superposed starch. As further evidence of a differentiation of the outer layer, he 

 found that weak iodine may penetrate to the inner part of the grain, coloring it blue without 

 in the least coloring the outer part (as had been found by Nageli). The outer layer he 

 believes is in the nature of a transition substance undergoing erosion or deposit. 



Further evidence that starch is not a uniform substance was found by Harz (Beiheft. 

 z. botan. Centralbl., 1905; Woch. f. Brau., 1905, xxii, 721) in experiments with solutions 

 of chromic acid, and chromic and sulphuric acids, in which the starch-grains were macerated 

 for 24 hours and then washed with cold water. Not only did the various kinds of starch, 

 but also different grains of the same starch, differ widely in theu- behavior; from which 

 Hiirz asserts that starch can not be a physically uniform substance which consists of 

 granules differing merely from each other according to a denser or looser constitution of 

 their ultimate complexes. He states that amylodextrin also did not behave like a uniform 

 substance, but seemed to be made up of a number of molecular groups which differ in com- 



