GENUS TRITICUM. 



365 



on edge they are lenticular, spindle-shaped, or occasionally either elliptical or plano-convex. In 

 addition, there are rarely some bean-shaped or reniform and hemispherical grains. The minute 

 grains are usually globular or ovoid, but occasionally hemispherical (perhaps broken grains) or 

 spindle-shaped. The outline of the large grains is often slightly irregular, which is chiefly due to 

 indentations on the surface which probably have been caused by the adherence and pressure of 

 small globular grains. A few of the grains are partially gelatinized, probably by the heat of grinding. 

 These two classes of grains represent non-identical forms of starch. In the photograph extremely 

 few of the small grains, which are very abundant, are shown. 



The hilum is not usually visible, but occasionally in the rather small, round grains it can be 

 seen as a clear spot. It is centric or slightly eccentric. There is in the center of the grains some- 

 times either a cavity or a cleft, and rarely there are several fissures which radiate from the center. 

 When the large grains are viewed on edge, a light, mesial longitudinal line is observed which has 

 somewhat the appearance of a cleft. 



The lamellce are rarely visible, but occasionally they can be determined on a part of the grain 

 as fine regular circles or parts of circles. In a few grains 8 to 10 were counted. 



The grains vary in size from the smaller, which are 2 by 2/i, to the larger, which are 38 by 34^. 

 The common size is 20ju. 



Polariscopic Properties. — The figure is usually centric, although occasionally slightly eccentric, 

 and while fairly distinct in the majority of the grains, it is very indistinct in many. The lines of 

 the figure are generally broad, and they broaden towards the margin of the grain. In a few grains 

 they are sharply defined, but in most they are very broad and diffused. The lines are commonly 

 straight; but they may be curved, or vary in thickness, or be bisected. 



The degree of polarization is low in the large grains to fair in the medium to smaller forms. It 

 is high when the large grains are observed on edge. There is usually some variation in the same 

 aspect of a grain. 



With selenite, in a great many of the grains, consisting chiefly of the largest, the quadrants are 

 not clearly marked and are generally somewhat irregular in shape and unequal in size. In the 

 small grains the quadrants are equal in size and regular in shape. The colors in the large grains 

 are usually not pure, but in the small grains they are pure. 



Iodine Reactions. — With a 0.25 per cent Lugol's solution all of the grains color a fair blue- 

 violet to a reddish- violet; with a 0.125 per cent solution they color lightly. After heating in water 

 until all the grains are completely gelatinized, the solu- 

 tion 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 gelatinized 

 grain-residues very lightly. The capsules, which are 

 much twisted and folded, color a red-violet with an excess 

 of iodine. 



Staining Reactions. — ^With gentian violet the grains 

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

 are very lightly stained. 



With safranin the grains begin to stain very lightly 

 at once, and in 30 minutes they are lightly stained. 



Temperature Reaction. — The temperature of gelatini- 

 zation is 63° to 65° C, mean 64°. 



Effects of Various Reagents. — With chloral hydrate- 

 iodine the reaction begins in some of the grains in 45 

 seconds, and in most of the grains in 3 minutes. In 30 

 minutes nearly all are affected, and one-fifth are com- 

 pletely gelatinized, with but little further change in an 

 hour. The reaction begins at one or at several points on 

 the margin. The starch at these places becomes dark and swells, often in the form of little rounded 

 protuberances. If several are:is are affected the process spreads along the margin from each point 

 until all of the marginal starch is affected. Then the process spreads inward over the rest of the 

 grain, often more rapidly from one or two points than from others. If the reaction begins at but 

 one part on the margin, the starch here dai-kens and swells, and the process spreads centrally, 



aartNo. 13. 



P I GV T 

 S 



Curve of Reaction-Intensities of Starch of Triticum 

 sativum var. vulgare. 



