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The Structure and Diagnostic Value of the Starch Grain. 



By K. B. Harvey. 



In view ol their conmimi (leciirreiice in plaut tissues, stareli i^rains 

 have been used, especially in IMiarnuicognos.v, to- differentiate between 

 ])lant-!. While there is a ;ireat variation in the size, shape and structure 

 of starch grains, tliose i)f different members of a genus, or even of a family, 

 often show a similarit\'. Hence, these group characteristics often may be 

 used to identify a given starch as belonging to a certain group of plants. 

 As medicin.al 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 starcli grain is 

 often of the gi'eatest diagnostic value. 



The cliaracters most of tt n use<l in the identitiiation <if starches are 

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

 are tlie hilum and the coi:centric layers of starch. It is very commonly 

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

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

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

 loss of moisture, and shrinking (if the central portion. 



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

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

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

 or miscell* of soluable starch, or granulose, imbedded in a frame woik 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 demonstrated by the action of such sol- 

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

 lose very rapidl.\', and leave a frame\^•ork of starch cellulose, of the same 

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

 characteristic color with iodine solution. 



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

 throughout the grain in A'erj' small crystals or triehites. A consideration 

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

 of this nature. The methods used in the preparati(ni of this paper, and 

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



