

PHYSICAL NATURE OF STARCH GRAINS 117 



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. Sehimper 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 /3 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 Allium Cepa, in the seed- 

 coats otChelidonium and in Oryza sativa, vzx.glutinosa, dextrin 

 and amylo-dextrin occur. On the other hand, the ordinary 

 grains which are coloured blue with iodine, are made up almost 

 entirely of sphaero-crystals of amylose arranged in layers. 



According to Kraemer,* the starch grains of the potato are 

 composed of colloid and crystalloid substances arranged in 

 lamellae which are distinct and separate one from the other. 

 At the point of origin of growth, the hilum, and in the alter- 

 nate lamellae, the colloid preponderates and is associated with 

 the crystalloid cellulose ; in the other lamellae the crystalloid 

 granulose is in the greater proportion. He also states that 

 the peripheral layer is elastic and porous, and may be an an- 



hydride of cellulose. Dennison also has expressed the view 

 that the outer layer of the grain is different from the more in- 

 ternal parts, and may be a carbohydrate not fully polymerized 

 t 4 -^ starch. 

 The view that both crystalloid and colloid materials occur 

 the starch grain is held by many, thus Mellanby,f by the 



* Kraemer : " Bot. Gaz.," 1902, 34. 

 fMellanby: " Biochem. Journ.," 1919, 13, 28, 



