STARCH-SUBSTANCE, AND THE STRUCTURE, ETC., OF THE STARCH-GRAIN. 23 



Small grains treated with iodine were colored yellow or gave no color reaction; and young 

 grains reacted very slowly, and the blue color was not so pronounced as in the older grains. 

 The parenchjana cells of Batatas edulis were found to contain large numbers of single 

 starch-grains. In later stages of development the grains by enlargement approach each 

 other, and ultimately form groups with the flattened surfaces of the grains in contact 

 with each other. At this stage the transition substance was still perceptible, but in older 

 cells it was absent. A compound grain he therefore regards as being nothing more than 

 two or more single grains whicli develop singly, and that later, owing to the disappearance 

 of the transition substance between them and by the development of a common outer 

 envelope, become one compound grain. 



The di\-ergent views as to whether the starch-grain grows by a stalactite-like deposi- 

 tion upon the outer surface or whether the grain, like the wood- or bast-fibers, increases 

 in size by a deposition watliin, led Harting (Botanische Zeit., 1855, xiii, 905) to an investi- 

 gation, from which he found that in the early stages of development of the starch-grain 

 an integument is present, this being especially prominent in the starch of the potato tuber. 

 This was colored brown with iodine, not blue like the starch-layers beneath it. According 

 to his view the integument belongs to the "epigon cell" which produces the starch-grain. 

 In the mature grain an integument was no longer discernible, all layers now being colored 

 blue with iodine. He believes that it must be this integument, or the integument of the 

 epigonen or mother cell, which holds the groups of grains together in such plants as Smilax 

 syphilitica. The similarity after absorption of water of the "cambial layer," or outer layer 

 of the starch-grain, to the cross-section of the cambial layer which produces wood- and 

 bast-fibers, is so striking that he beUeves one is warranted in the supposition that it is 

 the outermost layer of the starch winch is the cambial wall of the cell, and that the deeper 

 layers are formed later, and that while new layers are being formed on the inner surface 

 of the pre^'iously formed structure, the latter and the cambial wall increase in size through 

 intussusception. 



Reinsch (Neue Jalirbuch. f. Pharm., 1855, iii, 65) states that the granules of potato 

 starch contain dextrin and sugar already formed, which can be dissolved in water from the 

 pulverized grains. 



Melsens (Institut, Ire sect., 1857, xxv, 161; quoted by W. Nageli, Der Starkegruppe, 

 Leipzig, 1874) found that when starch-grains were treated with weak acids, pepsin, or dias- 

 tase they become so changed that they no longer yield a blue reaction with iodine, yet retain 

 their form, therefore having a non-starch skeleton or framework. 



In 1858 there appeared the elaborate monograph of Carl NageU (Die Starkekorner. 

 Morphologische, physiologische, chemisch-physicahsche und systematisch-botanische Mon- 

 ographic, Ziirich, 1858, 25 Tafellen, 625 S.) which covers a wide field of inquiry. To this 

 author chiefly is due the conception, which even to the present day receives almost uni- 

 versal acceptance, that the starch-grain consists fundamentally not only of two substances, 

 granulose and cellulose, but also that they have markedly different properties. The differ- 

 entiation of these components was brought about by subjecting raw starch to the action 

 of saliva for several months at 45 to 55 C. The larger portion of the grains was slowly 

 dissolved, while the remaining part was found to retain the form and structure of the 

 original grains. To the former he gave the name granulose and to the latter cellulose, 

 which latter he thought identical with the substance of the same name of plant structures, 

 and which he regarded, when obtained in this way, as being in its purest form. He looked 

 upon the grains as being mixtures of granulose and cellulose in which these substances 

 are combined in the form of a sort of a diffusion. The proportions of the two substances, 

 he records, differed in different kinds of starch and in the different layers of the same 

 grain, but the quantity of granulose was considerably greater than that of cellulose, the 

 latter being present often in very small quantities, probably representing only one-eighth 



