STARCH GRAIN AS A SPHEhOCRYSTAL 



by 



E. T. Reichert P. 75. 



The hypothesis of the crystalline structure of 

 starch was suggested by C. Nagell (Die Starkekorner ) , who 

 conceived the grain to be composed of minute crystalline 

 structural elements, which in his earlier writings he des- 

 ignates atoms, later molecules, and finally micellae, and 

 he attempted upon this hypothesis the support of the theory 

 of growth of the starch-grain by intussusception, the 

 explanation of the phenomBna of swelling, and optical and e 

 certain other properties of the starch-grain. Nageli writes 

 that the form of the ^arch-grain or molecule in its earliest 

 stages is unknown, and that while the grains or molecules 

 within their watery envelopes behave as regHBds their imper- 

 meability and growth by apposition in a similar manner to 

 crystals, it does not necessarily follow that they must agree 

 with crystals in respect to form; but to the contrary that it 

 is possible that lust those properties v/hich differentiate 

 them from crystals, that is, the chemical changes at the moment 

 of solidification and the attraction of the wfetery envelopes, 

 may prevent the development of a characteristically 

 crystalline shape. The analogy of the crystals, he also states, 

 does not necessarily lead to a similarity between the form 

 of the starch-molecule and that of the crystal. For other 

 reasons than those given it is probable, he states, that the 

 starch-molecule is originally spherical, which view he holds 

 receives the support in the spherical form of all starch-grains 

 in the earliest stages of development. The characters of the 

 starch-grain demonstrate that the molecules that were closely 

 arrancred in concentric lamellae and in radial rows had 

 eevidently, by a primary attraction (cohesion), been dis- 

 tribiited equally over the entire surface of the grain, thus 

 giving rise to the spherical form. The spherical molecules 

 always maintain this form when they develop singly, and are 

 free in a fluid medium, so that growth m.ay occur equally at 

 all points of the surface; but when they undergo unequal growth 

 upon different sides they soon deviate from their original 

 sphf-rical shape. If the molecules in one part of the grain are 

 still spherical and of equal size it indicates that they have 

 a favorable Environment. 



The movement of the particles of the solution he 

 conceives to pass preferably in a radial direction, and even if 

 all of the pnrticles in the solution do not closely follow 

 this course, yet it still is the prevailing one. The outer 

 and inner faces of each molecule become much more perpendicular 

 than the lateral face, on account of the movements of the par- 

 ticles, and also increase more rapidly at the poles tin an at 

 the equatorial zone, and thus become ellipsoidal. As they 

 deviate from the spherical form the water envelopes of the 



