STARCH-SUBSTANCR, AND THE STRUCTURE, ETC., OF THE STARCH-GRAIN. 53 



amylogen. He believes that starch (as well as the products obtained from it, such as Meyer's 

 a-amylose, Lintner and DiiU's amylodextrin, the granulose of various investigators, etc.) 

 consists of many amylogen molecules joined together in the form of carbinolanliydrid 

 combinations. (See Chapter III, p. 136.) 



Strasburger (Text-Book of Botany, 1903) supports the view of the existence of a 

 single fundamental substance, which, however, he admits exists in two forms in the grains, 

 one of which (the inner part) is soluble in water at 100° C, and the other (the outer part) 

 not soluble. He also notes that amylodextrin may be present, and that grains of certain 

 plants, such as Oryza saliva var. and Glutinosa may consist principally of amylodextrin, 

 and therefore color red with iodine. (See Alocasia, Chelidonium, and Macis.) 



Bloemendal (Woch. f. Brau., 1909, xxxiii, 436, 449) is also among the opponents of 

 Meyer's conception of the nature of the substances constituting the starch-grain. Bloe- 

 mendal studied the chemical composition of various starches, and came to the conclusion 

 that the a-amylose and ;9-amylose of Meyer correspond to the cellulose and amylose of 

 Niigeli, and if not identical differ only in water-content; and that the one form can be 

 readily transformed into the other. He states that no amylodextrin is found in normal 

 starch if sufficient care has been exercised in the course of preparation. (See page 170.) 



Pfeffer (The Physiology of Plants, 1900-6, 2d edition, 3 vols., Oxford, Trans. byEwart) 

 records that starch-grains remain within the chloroplastids or leucoplastids in which they 

 were produced until they are dissolved or removed, so that under normal conditions they 

 are never found lying free in the protoplasm or cell-sap. The grains are described as being 

 composed mainly or entirely of amylose, usually turning blue with iodine; but in certain 

 cases, as in the seed-coat of Chelidonium, Oryza, etc., they are recorded as being mainly 

 composed of amylodextrin, and other dextrins as well, so that a red coloration is produced 

 with iodine. These dextrinous substances are stated to be formed as intermediate products 

 of diastatic action, so that the starch-grains which redden with iodine may be regarded 

 as having undergone partial conversion into sugar. Starch-grains, whether formed by 

 cliloroplastids or leucoplastids, are able, he writes, by vii'tue of their power of imbibition 

 and swelling, to take up dissolved substances, and hence to interpolate new particles be- 

 tween the older ones. They might therefore, states Pfeffer, grow by intussusception, 

 although the researches of Schimper and Meyer have shown that starch-grains usually 

 grow by apposition. The structure and lamellation of the starch-grain, he holds, are 

 mainly the result of its growth by the apposition of successive layers, but, as in the cell, 

 secondary modification is possible by means of solvent and other agencies acting on the 

 surface of the starch-grain. Starch, like reserve cellulose, may be partially or entirely 

 dissolved when required for food, and hence at any time there may occur a solution or a 

 renewed deposition. A starch-grain does not dissolve only from the outer surface, but 

 also from witliin, so that frequently a skeleton of the grain is produced. Typical sphero- 

 crystals often dissolve in an equally i^ecuhar manner, and changes in the condition during 

 their formation may result in the production of denser layers than those first formed. 



Pfeffer records that the shape and growth of the starch-grain depend upon a variety 

 of factors, such as the specific character and activity of the amyloplastitl (leucoplastid 

 or chloroplastid), the position of the starch-grain in it, and also upon a number of condi- 

 tions wliich influence these and other relationships. Hence, starch-grains in the same 

 cell are not always precisely similar, while in diversely differentiated cells of the same plant 

 they may assume widely different shapes, as, for example, those in the lactiferous cells of 

 EupJwrbia when compared with those in other cells of the same plant. Usually the grain 

 continues to grow only so long as it is in contact with the plastid; and when the latter is 

 attached to one side only, growth takes place in this direction, and as a consequence an 

 eccentric lamellation results. The enlarging starch-grain, he states, not only regulates 

 its own growth by causing the distension and shifting of the plastid, but also, as in case 



