734 STARCHES OF IRIDACE^. 



Polariscopic Properties. The figure is usually eccentric and distinct, but not always clear-cut. 

 Its lines are usually thick and not sharp and often become thicker and less clear-cut as they approach 

 the margin. They are occasionally bent or otherwise distorted. 



The degree of polarization is fairly high. It varies considerably in different grains and in different 

 aspects of the same grain. It is slightly higher than in T. pottsii and distinctly higher than in T. crocata. 



With selenite the quadrants are fairly well defined and tend to be irregular in shape and unequal 

 in size. The colors are fairly pure. 



Iodine Reactions. With 0.25 per cent Lugol's solution the grains color fairly a blue-violet; 

 with 0.125 per cent solution they color lightly and the color deepens slowly. The color is deeper 

 than in T. pottsii, but about the same as T. crocata. After heating in water until the grains are com- 

 pletely gelatinized, the solution colors fairly and the grains deeply on the addition of iodine. Some 

 that are not so deeply colored have a violet capsule. After boiling for 2 minutes the solution colors 

 deeply and the grain-residues fairly. The capsules all have a violet color and most of them retain 

 more or less blue-reacting starch. 



Staining Reactions. With gentian violet the grains begin to stain at once and in 30 minutes 

 are lightly stained. The color is less than in T. pottsii, but slightly deeper than in T. crocata. 



With safranin the grains begin to stain at once and in 30 minutes are fairly well stained. The 

 color is slightly less than in T. pottsii and T. crocata. 



Temperature Reaction. The temperature of gelatinization is 72 to 74 C, mean 73. 



Effects of Various Reagents. With chloral hydrate-iodine reaction begins in most grains in IJ^ 

 minutes. About one-fourth are gelatinized in 15 minutes, two-thirds in 30 minutes, and three- 

 fourths in an hour. The reaction begins at the distal end of the grain and at the corners and angles 

 of the facets if these are present. The points at which the process starts become dark and swell 

 slightly, and from them it extends inwards until all the grain is gelatinized. The gelatinized grains 

 are not very large, are of a uniform dark color, and retain much of the original form of the grain. 

 The main difference between the gelatinized and the ungelatinized grains, apart from size, is that 

 in the former the corners and angles of the facets are more prominent. 



The reaction with chromic acid begins in most of the grains in 45 seconds, in all in a minute, 

 and is over in 4 minutes. The hilum swells slightly, fine striae appear radiating throughout the 

 grain, and a bubble appears at the hilum. The bubble swells as the hilum swells, up to a certain 

 point, then it begins to shrink and finally disappear. The inner portion of the grain is transformed 

 into a coarsely granular, gelatinized mass, the granules later becoming broken up and dissolved. 

 The marginal material forms a thick, coarsely striated band, which later is seen to be composed 

 of a row of coarse granules. This band becomes thinner and transparent as the grain swells, espe- 

 cially at the proximal end, where it is finally dissolved. The inner, gelatinous material flows out 

 and is dissolved, and the remaining portion of the marginal band subsequently slowly dissolves. 



Reaction with pyrogallic acid begins in most grains in a minute and in all in 13^ minutes. All 

 are partially and half completely gelatinized in 7 minutes, and all are completely gelatinized in 12 

 minutes. The reaction begins around the hilum, which swells shghtly; then fine striae are seen 

 radiating from the hilum in all directions throughout the grain; and a bubble of gas or air appears 

 above the hilum, which at first swells as the gi-ain swells, then decreases in size, and finally disappears. 

 The grain continues to swell and the inner portion is gelatinized, while the marginal part forms a 

 thick, finely striated ring, which becomes thinner and transparent. The gelatinized grains are 

 large, folded, wrinkled, and sacculated, and do not retain the original form of the grain. 



The reaction with/emc chloride begins in a few grains in 2 minutes. About half are completely 

 gelatinized in 12 minutes, four-fifths in 27 minutes, practically all in 45 minutes, and all in 1}4: hours. 

 The reaction usually begins at the hilum and consists in the formation of a bubble, which first 

 swells, then shrinks, and then disappears. The inner portion of the grain is rendered into a gelatin- 

 ous mass, and there is formed at the margin a thick band having a more or less homogeneous appear- 

 ance. This band gradually grows thirmer and transparent as the grain swells. In many grains, 

 however, the corners and edges of the facets become gelatinized and swell before the rest of the 

 grain is affected, but thereafter the process is the same as described. The gelatinized grains are 

 large, much folded, wrinkled, and crumpled, and retain little of the original form. 



With Purdy's solution the reaction begins very slightly in many grains in 2 minutes. In 15 

 minutes one or two of the grains are partially gelatinized, and in IJ^ hours all the grains are slightly 

 and a few nearly completely gelatinized. 



