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The Structure and Diagnostic Value op the Starch Grain. 



By K. B. Harvey. 



In view of their couuiiou nccurrence in plant tissuGt<. starch grains 

 liave been nsed, especially in I'harniacognosy, to differentiate between 

 jilant>'. While there is a great vari.itinu in the size, shape and strnctnre 

 of starch grains, those of different members of a genns, or even of a family, 

 often show a similarity. Hence, these gronp characteristics often may be 

 nsed to identify a given starch as belonging to a certain gronp of plants. 

 As medicinal action or value varies greatly between closely related mem- 

 bers of the same genus, it is of the highest importance to establish the 

 authenticity of the species, and in this determination the starch grain is 

 often of the greatest diagnostic value. 



The characters most often nsed in the identification of starches are 

 the size, .shape, and markings of the grains. The most distinct markings 

 are the hilum and the concentric layers of starch. It is very commonly 

 stated that the hilum is the point of attachment of the grain, and that it 

 occupies a position on tli(> surface, while in reality it is the part first 

 formed, and is marked by a fissure or cleft in the interior, caused by the 

 loss of moisture, and shrinking of the central portion. 



The starch grain has a structure somewhat similar to that of the 

 sphaero-CTystal, and like it grows by the apposition of new materials. 

 According to the best authorities, the grain is made up of minute crystals 

 or miscelltTe of soluable starch, or granulose, imbedded in a frame work of 

 starch cellulose. Alternate layers seen in many grains, contain a greater 

 proportion of granulose, and hence stain more deeply with iodine solution. 

 This structure of the grain was demonsti'ated by the action of sucli sol- 

 vents as chloral hydrate or diastatic solutions which dissolve the granu- 

 lose very rapidly, and leave a framework of starcli cellulose, of the same 

 size as the original grain, but lacking the substances which produce the 

 characteristic color with iodine solution. 



Hence, is was stated by Meyer that the soluble starch was distributed 

 throughout the grain in very small crystals or tricbites. A consideration 

 of the behavior of the grain upon swelling certainly demands a structure 

 of this nature. The methods nsed in the preparation of this paper, and 

 the results obtained agree with this structure, but indicate that the crystals 



