GLUCOSANS - 147 



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, on the other hand, 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 so-called micellae. He 

 held the view that the growth of the grain took place 

 not by apposition but by a process of intussusception, 

 that is to say, new material was intercalated between the 

 micellae, 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 sphsero-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 ^-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 of Chelidonium and in Oryza sativa, var. 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- 

 hydride of cellulose. Dennison also has expressed the view 

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

 internal parts, and may be a carbohydrate not fully poly- 

 merized to starch. 



* Kraemer : " Bot. Gaz.." 1902, 34, 341. 



TO* 



