STARCH-SUBSTANCE, AND THE STRUCTURE, ETC., OF THE STARCH-GRAIN. 59 



causes the outer layer to swell or to dissolve, the whole grain producing starch-paste; but 

 the starch does not go into complete solution, because undissolved flakes always remain 

 behind and take on a violet-color with iodine, while the solution turns blue. The process 

 of gelatinization also varied in starches of different origin. For instance, in acorns the 

 starch gelatinized only after being heated in water to 77.5 to 87.5 C, while the other 

 starches did so at a much lower temperature, the difference being due, he states, to the 

 richness of the starch in tannin. The presence of tannins also explains, he believes, the 

 failure to obtain starch-paste from raw boiled potatoes and from acorns. In fact, he found 

 that starch-paste will not be formed if the grains are boiled in a weak solution of tannic 

 acid. The starch in such a mixture is in flakes and the preparation can not be used as a 

 paste. The presence of tannin as a constituent, especially of the outer layer of the starch- 

 grain, is further indicated by the behavior of starch to iodine in solutions of calcium, 

 magnesium, and zinc chloride, of potassium bromide and potassium iodide, and of con- 

 centrated Ij^e. The action of these reagents depends, as revealed by the microscope, upon 

 the solution of the outer layer of the grain by these compounds. A certain power of resist- 

 ance to solutions of diastase is one of the peculiar properties of the outer layer. Starch- 

 grains were found to be affected by diastase only after the outer layer had here and there 

 been eroded by enzymes. 



St. Jentys attempted to prove by direct experiments the hypothesis that tannins 

 enter into the composition of the starch-grain. Potato starch was digested with concen- 

 trated sodium hydroxide, and from the solution substances were extracted by means of 

 concentrated alcohol which separated spontaneously from the solution, one of which was 

 obtained in crystalline form. These substances gave either a yellow or a copper-red reac- 

 tion with iodine, and also the characteristic color reaction for tannin with ferric chloride. 

 The alcoholic mother-liquor was colored greenish-yellow, and it also gave the tannin color 

 reaction with ferric chloride. The mass wliich was insoluble in concentrated lye and alcohol, 

 and which may be compared with Nageli's granulose, is dissolved readily in water, and 

 it is the substance in which a blue color with iodine predominated. Nor was this part of 

 the starch found to be of uniform composition, as was proved by the addition of a surplus 

 of iodine. The solution which at first was blue turned black, and after successive shakings 

 with chloroform and ether this black solution became violet and then blue, while bodies 

 staining a dark-red or yellow went into solutions in the chloroform and ether. Now that 

 the part which tannin plays in the iodine reaction, as well as in other reactions of starch, 

 was recognized, it was natural, St. Jentys writes, to suppose that the lamellated structure 

 of the grain is due to the presence of tannin. He states that when changes in concen- 

 tration occur, the formation of concentric layers must be caused by crystallized bodies 

 like tannins. In fact, from solutions of granulose, to which tannin had been added, and 

 allowed to evaporate, there separated lamellated structures resembling the most beautiful 

 starch-grains, such as are found in only a few plants like Dioscorea or Canna. Adding gallic 

 acid instead of tannin to a granulose solution caused a radial structure to appear with con- 

 centric lamellse, and the grains which separated from the solution resembled the starch-grains 

 of wheat, buckwheat, or Chinese sokyes, which is only the more remarkable inasmuch as the 

 grains with a more radially striated structure gave a more violet color, sometimes a red 

 color, with iodine, also a color smiilar to that of gaUic acid. The lamellated grains, as St. 

 Jentys found, could now be studied not only in granulose, but also with methyl-blue solu- 

 tions, these solutions being allowed to evaporate after the addition of tannic acid. 



St. Jentys states that in view of these phenomena it is clear that the starch-grain in 

 the plant is formed neither by apposition nor by intussusception, but by solidification of 

 concentrated solutions; and, furthermore, since tannins also possess the property of being 

 colored with iodine, not every part of the grain which shows a lamellated structure and 

 which is colored by iotline need necessarily be considered a carbohydrate. Since in the 



