PHYSICAL NATURE OF STARCH GRAINS 101 



the amylo-pectin. Amylo-pectin, moreover, tends to retard the 

 reversion of soluble amylo-cellulose into the insoluble form, and 

 hence there is a quantity of the soluble form present in the starch 

 granule which is able to dissolve in boiling water ; when, how- 

 ever, the amylo-pectin is removed, the pure insoluble amylo- 

 cellulose or amylose (as the authors prefer to call it) is 

 produced. 



A new form of soluble starch has recently been described 

 by Fernbach.* It is obtained by pouring a I or 2 per cent 

 aqueous suspension of potato starch into a large excess of pure 

 acetone and shaking vigorously ; a flocculent precipitate is 

 thus obtained, which, when filtered and ground up in a mortar 

 with more acetone and then dried in a vacuum, yields a light 

 white powder which is completely soluble in cold water. The 

 aqueous solution passes through filter paper and yields a very 

 pure blue colour with iodine. 



Brief mention may be made of the ideas held regarding the 

 physical nature of starch grains. As is well known, the gran- 

 ules not infrequently exhibit a more or less well-marked 

 stratification which years ago was thought to correspond to 

 the alternation of day and night. 



The "apposition" theory held that new layers were added 

 to those already formed, each layer being separated from the 

 next by a thin film of air. Nageli came to the conclusion that 

 the lamellation was due to the differences in the water-content 

 of the several layers, and that the grain was made up of minute 

 particles, the micellae, which are of the prismatic order, sur- 

 rounded by a film of water arid embedded in a matrix. The 

 growth of the grain took place by a process of intussusception, 

 that is to say, new material was intercalated between the mi- 

 cellae, and either gave rise to new micellae, or was used up in 

 increasing the size of the old ones. Schimper expressed the 

 idea that the grains were really of a sphaero-crystalline nature, 

 which view was modified by Meyer, who says that the grain 

 is made up of two kinds of needle-shaped crystals composed 

 respectively of a and ft amylose ; he also states that in those 

 grains which are coloured red with iodine, for example those 

 found in the cells of the root-cap of A Ilium Cepa, in the seed- 

 coats of Chelidonium and in Oryza sativa, \ax.glutinosa, dextrin 

 * Fernbach : " Conapt. rend.," 1912, 155, 617. 



