358 



STARCHES OF GRAMINACE^. 



aart No. 10. 



s 



PS CI PA I 

 "~ PC PS 



Curve of Reaction-Intensities of Starch of Andropogon 

 sorghum var. (White Kaffir Corn). 



Iodine Reactions. — With a 0.25 per cent Lugol's solution the grains all color a fairly deep violet, 

 with a 0.125 per cent solution they are lightly colored, but the shade does not deepen rapidly. 

 After heating in water until all the grains are completely gelatinized, the solution colors lightly and 

 the gelatinized grains very deeply on the addition of iodine. After boiling for 2 minutes the solution 

 colors very deeply, but the gelatinized grain-residues not at all. The capsules all color a red or 

 red-violet with an excess of iodine. 



Staining Reactions. — With gentian violet the grains 

 begin to stain at once, and in 30 minutes they are lightly 

 stained, some more than others. 



With safranin the grains begin to stain at once, and 

 in 30 minutes they are lightly stained, some more than 

 others. This stain is more effective than gentian violet. 



Temperature Reaction. — The temperature of gela- 

 tinization is 67 to 69° C, mean 68°. 



Effects of Various Reagents. — With chloral hydrate- 

 iodine the reaction begins in all of the grains in 45 seconds, 

 it is over in nearly all in 8 minutes, and in all in 15 min- 

 utes. The grains first color a bright violet, which be- 

 comes very dark. The reaction begins at the prominent 

 angles and corners of the grain, at which points the 

 starch becomes dark, but does not swell very much. 

 The process then proceeds into the interior of the grain, 

 first along a number of straight lines converging towards 

 the hilum. The starch along these lines becomes dark, 

 then the starch between them darkens, usually more 

 rapidly on one side of the grain than on the other. When the whole grain is darkened it swells 

 somewhat. The gelatinized grains are not very large, they arc of a uniform dark color, and retain 

 some of the original form, but often are more rounded than the normal grains. 



The reaction with chromic acid begins in some of the grains in 20 seconds and is over in 2J-^ 

 minutes. The grain first shows a number of very distinct strijB radiating from the hilum to the 

 margin. Then the central portion becomes coarsely granular and melts down into a*semiliquid 

 mass, and the grain swells. The resistant portions of the grain form a very broad, distinctly 

 striated band which gradually becomes thinner. Finally, one or two of the outer layers of 

 the grain peel off, and the marginal band already described is dissolved at one or two places. 

 The pieces thus separated float away from one another, and the semiliquid starch in the interior 

 of the grain flows out, and is entirely dissolved. The rest of the marginal band also dissolves 

 very rapidly. 



The reaction begins in 30 seconds with pyrogallic acid, and is over in 2 minutes. The grain 

 first shows a number of very distinct striae which radiate from the hilum to the margin; then the 

 starch about the hilum becomes a granular mass and the grain swells. The more resistant starch 

 forms a broad, striated band at the margin. This band becomes thinner and homogeneous in ap- 

 pearance as the grain continues to swell, and finally forms a rather thick limiting envelope, while 

 at the same time the starch in the interior of the grain is changed to a gelatinous, granular mass. 

 The granules finally disappear with the formation of a completely gelatinized grain. The gelati- 

 nized grains are large, and the capsules are usually folded, wrinkled, and creased, thus distorting 

 the original form of the grain. 



With ferric chloride the reaction begins in many of the grains in a minute. It is over in most of 

 the grains in 10 minutes and in all in 20 minutes. The reaction begins at one side of the grain, 

 usually at the prominent comers and angles. The starch here becomes gelatinous and the process 

 spreads over the rest of that side, then inward over the whole grain. Small portions become broken 

 from the ungelatinized portion and are gelatinized; finally, the whole mass is broken up into two or 

 three pieces, which become gelatinized. The gelatinized grains are large, with thin, much wrinkled, 

 folded, and creased capsules. In some grains the reaction begins in the interior of the grain in the 

 region of the hilum. The starch at this point becomes gelatinous and the grain swells, the less 

 resistant starch forming a gelatinous mass in the interior, and the more resistant starch a broad, 

 homogeneous-looking band at the margin, which becomes very thin as the grain swells. 



