410 STORAGE SYSTEM 



Where the grains are closely crowded together, on the other hand, they 

 tend to assume polyhedral shapes as a result of mutual interference. 

 In the endosperm of Indian Corn, for example, the starch-grains of the 

 " horny " endosperm are all polyhedral, whereas in the " mealy " portion 

 rounded grains predominate. 



In addition to the ordinary or simple starch-grains, various com- 

 pound forms also exist ; these often resemble ordinary grains in shape, 

 but on closer examination are found to be made up of two or more 

 sometimes of several hundreds of partial grains. Even where the 

 starch-grains are normally simple, they are almost invariably accom- 

 panied by a certain number of compound grains {e.g. in Potato, Wheat, 

 etc.). Conversely, the compound forms are numerous, and the simple 

 grains few and scattered, in the endosperm of Oat and Eice, and in 

 many other cases. Compound grains may be further classified under 

 the headings of completely compound and partially compound forms. 

 In the former type the planes of separation between the component 

 grains extend to the surface ; in the latter case, the partial grains are 

 enveloped in a certain number of common layers. 



As regards their chemical composition, starch-grains consist of 

 several different carbohydrates all represented by the empirical 

 formula (C 6 H 10 O 5 ) ?1 together with water and a small amount of mineral 

 substance. According to Nageli, every starch-grain is principally com- 

 posed of granuloses this is the substance that is responsible for the familiar 

 blue iodine-reaction of starch. The granulose is contained in the meshes of 

 a delicate framework of " starch-cellulose " ; this persists as a skeleton, 

 when the granulose is removed by the action of solvents, such as saliva 

 or dilute mineral acid. A. Meyer, on the contrary, believes that the 

 majority of starch-grains consist of a single substance which he terms 

 ami/lose; he distinguishes between two varieties of this body, namely, 

 3-amylose, which deliquesces in contact with boiling water, and a-amylosc, 

 which remains solid under the same conditions. The /^-compound 

 corresponds to Nageli's granulose, the a-variety to his starch-cellulose. 

 Opinions differ as to the nature of the skeleton which is left, when a 

 starch-grain breaks up under the influence of saliva or mineral acid. 

 The starch-grains of certain forms of Eice and Millet {Oryza saliva, 

 var. glutinosa and Sorghum vulgare, var. glutinosum) assume a reddish 

 hue, in place of the normal blue coloration, on treatment with iodine. 

 According to Meyer, these abnormal starch-grains consist principally 

 of amylodi'xtrinc, a [hydrolytic] derivative of amylose ; Butschli, on 

 the other hand, assumes that a special amylaceous carbohydrate, 

 imyloerythrine, is present in such cases. 



With regard to the physical structure of starch-grains, it may first 

 of all be stated that each grain consists of a number usually a large 



