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



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

 order of the parts being from the margin inward. 



Table 1. 



Table 2. 



A (in water). 



B (in iodine). 



a. Highly refractive region, a'. Layer which has not so 



fully taken on the nature 

 of starch, hence is faintly 

 blue in color, a". A blue 

 starch layer. 



1. A dark line, probably a ' This layer is broader and 



crack filled with watery 

 colloidal mass. 

 h. Highly refractive layer. 



2. A dark line similar to 1. 

 c. Slightly refractive layer. 



paler in color. 



and 



Contracted slightly 



stains blue, 

 c and layers anterior to c 



have contracted, leaving 



space at 2. 

 In iodine this layer stains 



uniformly with those next 



to it on inside. It is pale 



blue in color. 



C (in alcohol). 



This layer is now pale blue 

 in color, the color becom- 

 ing lighter from inside 

 toward periphery. There 

 is no sharp line separat- 

 ing two parts. 



In alcohol this layer is still 

 broader. 



Contracted a little more 

 and blue partly removed. 



Contraction goes on with 

 consequent broadening 

 of 2. 



This iodine is easily remov- 

 ed, leaving layer jjale 

 blue in color. 



D (in gentian violet and 

 orange G). 



The layer a' is of different 

 composition and takes 

 orange; a" is starch and 

 takes gentian violet like 

 rest of grain. 



This layer is about the 

 same width as in alcohol. 

 It stains pale blue. 



Characteristic blue with 

 gentian violet. 



Stains pale blue, contains 

 relatively small amount 

 of starch. 



This layer stains less deep- 

 ly than a or h. 



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. cit., p. 51) and Fischer {he. cit., p. 55), the less dense. The limitation of the orange 

 layer, he holds, can not be due to hindrance 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 different 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 natm-e 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 cliromic 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 their behavior; from which 

 Harz 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- 



