GENTJ8 HORDEUM. 



373 



Curve of Reaction-Intensities of Starch of Hordeum 

 sativum var. (Champion), 



With selenite, in most of tlie small grains the quadrants are well defined, regular in shape, and 

 usually equal in size. The colors are pure. In the large grains the quadrants are not as a rule well 

 defined, and are often irregular in shape and of unequal size. The colors are not pure. 



Iodine Reactions. — With a 0.25 per cent Lugol's solution the grains all begin to color a rather 

 light blue-violet to violet; with a 0.125 per cent solution they color very lightly, and the color deepens 

 fairly rapidly. After heating in water until all the grains 

 are completely gelatinized, the solution colors fairly and 

 the gelatinized grains very deeply on the addition of 

 iodine. After boiling for 2 minutes the solution colors very 

 deeply, but most of the grain-residues do not color at all. 

 The capsules all color a red- violet with an excess of iodine. 



Staining Reactions. — With gentian violet the grains 

 begin to stain very lightly at once, but in 30 minutes 

 they are still very lightly stained. 



With safranin the grains begin to stain very lightly at 

 once, but in 30 minutes they are still very lightly stained. 



Temperature Reaction. — The temperature of gelat- 

 inization is 60° to 62° C, mean 61°. 



Effects of Various Reagents. — With chloral hydrate- 

 iodine the reaction begins in most of the grains in IJ^ 

 to 2 minutes; about one-fourth are gelatinized in 30 

 minutes, and one-half in an hour. The reaction begins 

 at one or less often at two points on the margin, where the 

 starch becomes dark and swells somewhat. The reaction 

 spreads over the rest of the grain, usually slightly more 

 rapidly over the marginal starch than over the inner parts of the grain, until only the part oppo- 

 site the point at which the coloration began remains unaffected. This finally is gelatinized. The 

 gelatinized grains are not very large, and they retain much of their original form. 



The reaction with chromic add begins in from 10 to 20 seconds and is over in 2}4, minutes. 

 The hilum often becomes distinct, or the central portion of the grain assumes a granular appearance. 

 Fine stria; appear radiating from the hilum or central portion in all directions. The less resistant 

 portions of the grain are now changed into a somewhat granular semiliquid mass, which occupies 

 the central portion of the grain, attended by swelling of the grain. The more resistant outer starch 

 in some cases remains in place until the starch in other parts is dissolved. This resistant starch 

 forms a rather thin, striated marginal ring, which becomes thinner and transparent until it is only 

 a thin capsule, which incloses a granular gelatinous mass. This capsule is dissolved at one point, 

 and through this opening the semifluid gelatinized starch pours out and is dissolved, followed by 

 solution of the remainder of the capsule. 



With pyrogallic acid the reaction begins in many of the grains in 30 seconds and is over in 2 

 minutes. The central portion of the grain assumes a granular appearance, and in some grains the 

 hilum becomes distinct and fine strise appear radiating from the central portion. The less resistant 

 starch passes into a semiliquid mass and the grain swells. The more resistant outer starch retains 

 for the most part its original position and presents the appearance of a munber of irregular rings, 

 or parts of rings, of varying breadth and density, located between the central portion of the grain 

 and the margin. These rings become thin and clearer, but they never entirely disappear. The 

 gelatinized grains are fairly large and often retain much of the original form of the grain. Their 

 capsules are sometimes much wrinkled, folded, and twisted. 



The reaction begins in a few grains in a minute with ferric chloride. It is over in one-half of the 

 grains in 15 minutes, in two-thirds in 35 minutes, and in nearly all in an hour. The reaction begins 

 at one or two points on the margin. At these points the starch becomes gelatinous and swells out 

 irregularly, and from them the reaction spreads quite uniformly over the whole grain. The gelat- 

 inized grains are large, but do not retain much of the original form of the grain. The capsules 

 are very much wrinkled and folded. 



The reaction with Purdy's solution begins in some grains in IH minutes, but there is little 

 further change at the end of an hour. The reaction, as far as it goes, appears to possess the same 

 characteristics as that with pyrogallic acid. 



