418 



STAKCHES OF POLYGONACEiB. 



STARCHES OF POLYGONACEyt 



Class, Dicotyledones. Order, Polygonales. Family, Polygonaceae. Genus 



represented, Polygonum. 



GENUS POLYGONUM. 



The starch of only one representative of one genus of this family was studied. Polygonum fago- 

 pyrum Linn., usually designated Fagopyrum esculentum Moench., the common buckwheat of the 

 agriculturist and of commerce, is a native of Central Asia, and cultivated chiefly in the northern and 

 central parts of the United States. From the seeds is made a commercial flour rich in starch. The 

 starches from two agricultural varieties, known as American and Japanese buckwheat, respectively, 

 were examined. 



STARCH OF POLYGONUM FAGOPYRUM VAR. (AMERICAN). (Plate 10, figa. 59 and 60. Chart 62.) 



Histological Characteristics. — In forjn the grains are probably solely simple and for the most 

 part isolated, and in part in aggregates of two or more components. Pressure facets are foimd on 

 many of the grains. The conspicuous forms of the simple grains are polygonal, either with sharp 

 or generally much-rounded angles, and round. The conspicuous forms of the aggregates are several 

 grains arranged linearly, straight or curved, or in oval or irregularly shaped masses. 



A cavity is usually found at the hilum, from which radiating fissures emerge. The hilum some- 

 times appears as a clear spot, centric or slightly eccentric 

 in position. 



The lamellcB are not visible. 



The grains vary in size from the smaller grains, which 

 are 2/i, to the larger, which are 14ix. The common size 

 is about T/i. 



Polariscopic Properties. — The figure is centric or 

 slightly eccentric, and distinct. The lines are rather 

 fine and generally straight, but may be bent and rarely 

 bisected. The figure is in the form of a cro.ss. 



The degree of polarization is fair to rather high, with 

 frequent variation in the same aspect of a grain and also 

 in different grains. 



With selenite the quadrants are clearly defined, and 

 in some grains of about equal size and regular in shape; 

 but they mostly vary slightly in size and shape. The 

 colors are generally pure. 



Iodine Reactions. — With 0.25 per cent Lugol's solu- 

 tion most grains color a light violet, a few rather deeply, 

 and the tint deepens slowly; with 0.125 per cent solution 

 the grains assume a light reddish-violet tint, some rather deeper than others, and the color deepens 

 within 5 minutes. After heating in water until all the grains are gelatinized, the solution colors a 

 deep indigo-blue and the gelatinized grains a deep blue-violet on the addition of iodine. After boil- 

 ing for 2 minutes, the solution colors a still deeper indigo-blue and the grain-residues either only 

 very lightly or not at all. The capsules assume a deep reddish-purple or heliotrope tint when an 

 excess of iodine is added. 



Staining Reactions. — ^With gentian violet and with safranin the grains begin to stain very lightly 

 at once and in 30 minutes they are still only lightly colored. 



Temperature Reaction. — The temperature of gelatinization is 63° to 64° C, mean 63.5°. 



Effects of Varioiis Reagents. — With chloral hydrate-iodine the reaction begins at once in all 

 the grains. All but rare resistant grains are gelatinized in a minute, and all in 8 minutes. The 

 reaction begins at the corners and edges of the facets, the starch at these points becoming dark and 

 swelling slightly, and the process proceeds from these points all over the grain quite evenly. The 

 gelatinized grains are not very large and retain much of their original form. They have a central, 

 round, light space surrounded by a broad, marginal band of starch that is colored dark indigo. 



Curve of Reaction-Intensities of Starch of Polygonum 

 fagopyrum var. (American). 



