STARCH-SUBSTANCE, AND THE STRUCTURE, ETC., OF THE STARCH-GRAIN. 29 



vary in density, the outermost and densest part resisting all action of chemical substances 

 longer than the less dense layers by whicli the latter are surrounded and impregnated. 



In further investigations of the constitutcnts and decomposition products of starch, 

 Jessen (Jour. f. prakt. Chemie, 1868, cv, 65) concludes that starch-grains are composed 

 mainly of three constitutcnts: (1) the envelopes, or cell-membranes, or integuments, 

 which are insoluble in hot or cold water (the amidine tegumentaire of Gu^rin-Varry) ; 

 (2) the starch-substance, or amylogcn, which is soluble in cold water (the amidone of Payen 

 andPersoz; the amylogcn of Delffs ; and the amidine of Guerin-Varry etc.) ; (3) starch which 

 is insoluble in cold water, but soluble in water at 55 to 80 C., which may be called amijlin 

 (the amidin-soluble of Guerin-Varry, and the amylin of IVIaschke, Delffs, Melsens, and Fr. 

 Schultze). Other constituents were found to be present in very small quantities, and in 

 ordinary analyses some of them may be entirely overlooked. Some of the minor constitu- 

 ents, he states, are dextrin (in wheat, pointed out by JVIaschke); chlorophyl and wax (in 

 potato, according to Guerin-Varry); nitrogen (0.1 to 0.25 per cent); fat, soluble in alcohol 

 (0.001 per cent in potato and 0.0005 to 0.006 per cent in wheat, according to Rousseau). 



The envelope, Jessen states, forms only a small part of the grain (2.96 per cent accord- 

 ing to Guerin-Varry; 5.7 per cent in potato, 3.1 per cent in maranta, and 2.3 per cent in 

 wheat according to Fr. Schultze; and 4.8 per cent according to Payen and Pensoz). By 

 continued boiling the envelopes pass more or less into solution, and they behave generally 

 like other cell membranes and give the reactions for cellulose. Often they became blue 

 in the presence of iodine, owing, he assumes, to adherent particles of starch. He states 

 that when these are removed the envelopes are colored with iodine only upon the addition 

 of chloride of zinc, dilute sulphuric acid, etc. 



The proportions of amylogen and amylin Jessen gives as 58.68 per cent and 38.38 

 per cent respectively. He accepts the figures of Guerin-Varry (60.45 and 39.55 respec- 

 tively), although he asserts that the proportion of amylogen is probably less. Both sub- 

 stances yield a blue reaction with iodine. The amylogen exists chiefly in the inner parts 

 of the grains, and it can be obtained by placing the crushed grains in cold water. The 

 inner layers he believes to be the youngest. Starch-paste he holds is neither a simple 

 substance nor a chemical compound, but a mechanical mixture of all of the constituents 

 of the grains. Amylogen, he found, passes into dextrin very readily, far more readily 

 than amylin; and the transformation occurs in a pure solution at room temperatures after 

 2 to 3 days. Whether or not amylogen and amylin of different kinds of starches are differ- 

 ent, he does not know; and he states that very little is known about the composition and 

 properties of amylogen, and that in chemical composition amjdogen and amylin may be 

 the same. 



Sachs (Text-Book of Botany, 1875) adopts in modified form Nageli's view of the 

 two proximate constituents of starch. He states that every grain of starch consists of 

 starch, water, and inorganic substances. The starch has the same percentage composi- 

 tion as cellulose, to which it bears the greatest similarity of all known substances in both 

 chemical and morphological properties. It occurs in the grain in two forms: one, granu- 

 lose, which is the more easily soluble and which gives a blue reaction with iodine ; and the 

 other, starch-cellulose, which shows less solubility and wliich comes nearer to cellulose. 

 Both occur in every part of the grain. If the granulose is extracted, the celluolse remains 

 behind as a skeleton which shows the internal organization of the whole grain, but is less 

 dense, and its weight represents only about 2 to 6 per cent of the weight of the whole grain. 

 The internal organization of the grain he holds is not homogeneous, and that it differs in 

 relation to the varying proportions of water in the several parts. Every part of the grain 

 contains water, the amount usually increasing from without inwards, and attaining a 

 maximum at a fixed point in the interior. With the increase in the proportion of water 

 there is a decrease in cohesion and density, and also in refractivity, on which partl^^ the 



