STARCH-GRAIN AS A SPHEROCRYSTAL. 75 



6. When, therefore, a round pea is crossed with a wrinkled pea, four separately heritable charac- 

 ters are dealt with: (a) the shape of the pea, whether round or wrinkled; (6) the absorption 

 capacity of the pea as regards water, whether low or high; (f) the shape of the starch-grain, 

 whether long or round; (d) the constitution of the starch-grain, whether single or compound! 



(A study of the effects of hybridization, etc., upon the properties of starch and other 

 corresponding substances is now being carried on by the author of the present memoir.) 



STAKCH-GKAIN AS A SPHEKOCKYSTAL. 



The hypothesis of the crystalline structure of starch was suggested by C. Niigeli (Die 

 Starkekorner, etc., loc. cit.; Botanische Zeitung, 1881, xxxix, 633), who conceived the 

 grain to be composed of minute crystalhne structural elements, which in his earlier writings 

 he designates atoms, later molecules, and finally rnicellw, and he attempted upon this 

 hypothesis the support of tlie theory of growth of the starch-grain by intussusception, 

 the explanation of the phenomena of swelling, and optical and certain other properties 

 of the starch-grain. Niigeli writes that the form of the starch-grain or molecule in its 

 earliest stages is unknown, and that while the grains or molecules within their watery 

 envelopes behave as regards their impermeability 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 just those properties which 

 differentiate them from crystals, that is, the chemical changes at the moment of solidifica- 

 tion and the attraction of the watery envelopes, may prevent the development of a char- 

 acteristic crystalhne 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 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 arrranged in concentric lamella? and in radial rows 

 had evidently, by a primary attraction (cohesion), been distributed 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 may occur equally at all points of the surface; but when they undergo unequal 

 growth upon different sides they soon deviate from their original spherical 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 particles 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 particles, and also 

 increase more rapidly at the poles than at the equatorial zone, and tlius become ellipsoidal. 

 As they deviate from the spherical form the water envelopes of the molecules also show an 

 unequal density, since the greater diameter corresponds to the less dense envelope. This is 

 a cause for the molecules at the poles now developing a greater mass than at the lateral 

 surfaces, and this theory also agrees with the facts already given that there is less water 

 lodged between the molecules in the radial than in the tangential direction. In the trans- 

 verse (tangential) section of the molecule, the interstices between the 3 or 4 molecules which 

 lie beside one another are triangular or quadrangular. Now only these sides of the mole- 

 cule and the angles which are turned towards the interstices have a chance of having par- 

 ticles from the solution deposited upon them with considerable force and thus growing by 

 the deposit of material. The transverse section of the molecule has become angular, with 

 the angles turned towards the interstices, which have become narrowed. This alteration 

 from the circular cross-section under similar conditions continues and even increases. 



