80 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



which may be (hic to molecular differences in the component starch-substances. The 

 outermost or capsular layer is the least soluble in both hot and cold water; it is less 

 digestible in weak acids and enzymes; it gives different color reactions upon certain con- 

 ditions; and it shows a different degree of resistance to the actions of chloral hydrate and 

 other reagents. Grains of some plants may yield a piu-ple, violet, or red reaction with iodine, 

 owing, it may be, to the presence of erythrodextrin, but grains which at first become blue 

 may exhibit a range of colors from a purple to a violet and red upon the exposure to the air. 

 ^^^len starches have been subjected to swelling agents, and the capsular layer is thus dis- 

 organized, the inner part may stain an intense indigo blue, while the capsular portion may 

 be colored blue, purple, violet, red, etc. The grains of certain plants apparently do not 

 contain ordinary starch, but in its place a modified form or a mixture of ordinary starch 

 and erythrodextrin, or erytlirodextrin, and therefore stain a red-violet or a red with iodine, 

 as reported in the case of the grains of Oryza sativa (red violet) and Glutinosa, of the seed- 

 coats of Chelidomum, and of the arillode of the seed of Myrislica, etc. 



The use of specific terms to signify that the outer or capsular part of the grain is a 

 non-starch substance, as, for instance, the term "cellulose" of Nageli, and "amylocellu- 

 lose," is misleading and unwarranted, as there is no good reason for believing that this 

 part is other than a modified form of a typical starch-substance. The term "amylo- 

 dextrin" is as objectionable as amylocellulose, etc., as it infers a form of dextrin entirely 

 apart from the tnie dextrins, or a mixture of starch and dextrin; and, moreover, it is 

 used by different authors to signify very different boches. The assumption that starch- 

 substance exists in modified forms in the grains of different starches and in grains of the 

 same starch and in any given grain, and that erythrodextrin may be present especially 

 in the capsular parts, and that erythrodextrin may replace starch in the grains of certain 

 species, are sufficient, upon the basis of the literature quoted, to satisfactorily account 

 for the essential differences in the beha\'ior of different grains and of different parts of a 

 given grain towards iodine and other agents. 



(2) The cause of the insolubility of uninjured raw starch-grains in cold water seems 

 to be attributable to some form of protective covering which is deposited by the starch- 

 forming structure or by the cell-sap. That such a protective exists is inchcated by the 

 fact that any condition which destroys the continuity of this coating, such as the rupture 

 of the grain by grinding with sand or glass, or the erosion of the grains by bacteria or 

 diastase, or the gelatinization or solution of the coats by potassium hydrate and \'arious 

 other agents, renders the grains soluble in cold water and is equivalent to gelatinization 

 liroi)ortional in degree to the extent of exposure of the intra-integumentary portion. It 

 would seem that such a protective covering might be for the purpose of preventing the 

 solution of the starch-grain in the cell-sap, yet not interfere with the action of diastase, 

 which is rendered effective by changed conditions in the composition of the cell contents 

 when a consumption of starch for pabulum is rendered necessary. Assuming that starch 

 is produced tlu'ough the agency of enzymes, it follows, as a corollary, that by virtue of 

 the reversibility of the actions of these substances it is broken down when needed for 

 pabulum into the bodies identical with or similar to those from which it was formed. 



(3) The starch-grain at its earliest period of formation is spherical and homogeneous, 

 and during growth tends to develop a liilum and lamella; and undergo changes in form 

 which, sometimes at least, are more or less characteristic of the species, genus, and family. 

 Both hilum and lamellse are more or less variable in their properties in different starches, 

 and the lamellie of any given grain may differ from one another in density and coarseness 

 and other features. The mechanism of the formation of the hilum can probably be ac- 

 counted for by the factors which give rise to a siinilar phenomenon in the formation of 

 otlier spherocrystals, and in the apparently similar conditions which attend the formation 

 of a core and radial fissures during the solidification of molten metals. The starch-grain 



