GENERA PANICUM AND OBTZA. 363 



first, and then the central portions of the grain. The gelatinized grains are not very large and 

 retain much of the original forms. They usually appear to consist of a light central portion sur- 

 rounded by a fairly broad, dark, marginal band. 



The reaction with chromic add begins in a few seconds and is over in 2 minutes. The hilum 

 becomes clear and is connected with the corners of the facets by clear lines that are formed probably 

 by the gelatinization of the less resistant starch. The grain swells, and the more resistant starch is 

 divided into several parts which lie along the margin. As the grain continues to swell these pieces 

 of ungelatinized starch are forced further and further apart and are gradually gelatinized and trans- 

 formed into a thin, transparent envelope. This envelope is dissolved at one or two points, and the 

 contents flow out and dissolve, followed by solution of the rest of the envelope. 



With pyrogallic acid the reaction begins in most of the grains in 30 seconds to a minute, and 

 is over in 8 minutes. The reaction starts at the hilum, which grows clearer. The less resistant 

 starch of the grain becomes gelatinous and occupies the central part, and the more resistant starch 

 is pushed peripherally and forms a fairly broad, dense band. This band becomes rather slowly 

 less broad and less dense until finally it is quite transparent. The gelatinized grains are fairly 

 large and retain much of their original form. 



The reaction with ferric chloride begins in a few grains in 2 minutes and is over in 25 minutes. 

 The hilum becomes clear, and the less resistant starch is gelatinized and occupies the central part 

 of the grain, while as the grain swells the more resistant starch is pushed out to form a fairly broad, 

 dense, marginal band. This band becomes less broad and dense, until it is only a thin transparent 

 capsule. The gelatinized grains are large, but they do not retain much of their original form. The 

 capsules are often much folded and wrinkled. 



With Purdy's solution there is a slight reaction in a few grains in 4 minutes and but little fur- 

 ther change in an hour. 



GENUS ORYZA. 



According to Hitchcock, Oryza is a tropical genus of six species. 0. saliva Linn, is originally 

 native to the Old World tropics, but now naturaUzed in Brazil and cultivated extensively in China 

 and India and in the coast region of the southern United States. It yields the rice of commerce. 

 Starch from an unnamed agricultural form of 0. saliva was studied as a type of the genus. 



STARCH OF ORYZA SATIVA VAR. (Plate 2, figs. 7 and 8. Chart 14.) 



Hislological Characlerislics. — In form the grains are simple, but frequently observed either in 

 oval or rounded aggregates which consist of from two to many components. Pressure facets, vari- 

 able in number, are present on the isolated grains. The conspicuous form of the isolated grains is 

 sharply polygonal and even crystalline in character. The number of angles varies, but the pentag- 

 onal type rather predominates. Rarely oval grains with one margin rounded and the other flat- 

 tened or concave are found. The conspicuous forms of the aggregates are somewhat rounded or 

 ovoid. They closely resemble those found in the oats, but the angular character of the component 

 grains is more marked and the aggregates break up more readily into individual grains. 



The hilum is usually centric and may appear either as a round central spot or as a cleft, but 

 generally it can not be distinguished. 



The lamellw are not visible. 



The simple grains vary in size from 1 by 1/* to 8 by 6ju. The common size is 5ji. The aggre- 

 gates are as large as 30 by 20/i. 



Polariscopic Properties. — The figure is usually centric, but so small that its details can not be 

 determined. The lines appear to be straight and at right angles, so as to form a cross. 



The degree of polarization is low to fair. The grains are so minute that it is impossible to de- 

 termine clearly whether there are any variations in the same aspect of a grain. 



With selenite the quadrants are so very small that it is impossible to determine in most cases 

 their relative shape and size. They appear, as a rule, to be irregular in shape and unequal in size. 

 The colors are usually not pure. 



Iodine Reactions. — With a 0.25 per cent Lugol's solution, the grains are colored a light violet 

 with a slight reddish tint, and the color deepens rather slowly; with a 0.125 per cent solution they 

 stain a light reddish-violet, the color deepening rather slowly. After heating in water until the 

 grains are completely gelatinized, the solution colors a deep blue with a reddish tint and the grains 



