GENKRA AVENA AND ARRHENATHEUUM. 375 



EJh'cts of Vurious haujcntg. With chloral hydndc-iodinc the reaction begins in oO seeonds to 

 a minute and is over in 8 minutes. The reaction originates at the jiromineut angles and edges of 

 tlie facets, whicli dari<en and swell slightly, and from these jioints it spreads inward evenly and 

 without much swelling over the rest of the grain. The gelatinized grains are not very large and retain 

 much of the original form of the grain. They have a central light jwrtion surrounded bj^ a broad 

 mai'ginal band of dark starch. 



The reaction ^vith chromic acid begins at once and is over in 40 seconds. It is so rapid that it 

 was impossible to distinguish the different steps. 



With pyrogalUc acid the reaction begins in 15 to 30 seconds and is f)ver in 13^9 minutes. The 

 hihan becomes distinct and clear, and clear lines often extend from the liihun nearly to the angles 

 of the facets. The grain swells as the less resistant starch becomes gelatinous, forming a large mass 

 which is clear in the central portion and has a fairly broad, dense marginal band formed by the more 

 resistant outer starch. This band is less dense and not so liroad at the angles of the facets, and it 

 becomes transparent and less broad and dense, until finally there remains only a thin, transparent 

 capsule. The gelatinized grains are large and retain some of their original form. The capsules 

 are often A\Tinkled, crumpled, and folded. The components of the aggregates often separate or 

 partially separate from one another during the process of gelatinization. 



The reaction with ferric chloride begins in many grains in a minute and is over in 10 minutes. 

 The reaction starts at the angles and edges of the facets, and the starch at these points becomes 

 gelatinous and swells out irregularlj'. The hilum now becomes distinct, and the less resistant starch 

 of the inner part of the grain gelatinizes, causing the grain to swell. The resistant marginal starch 

 is gelatinized at first only at the angles and edges of the facets, but later all parts become gelatinous. 

 The gelatinized grains are very large and retain some of the original form of the grain. The cap- 

 sules are often wTinkled anil crumpled. 



The reaction with Purdy's solution begins in some of the grains in a minute and in 20 minutes about 

 one-fourth are partially or completely gelatinized. The reaction is very incomjilete at the end of an 

 hour. The reaction, as far as it goes, presents the same appearances as that with pyrogallic acid. 



GENUS ARRHENATHERUM. 



This is a genus of pasture grasses. One member, commonly known as Avena elatior Beauv., 

 is of agricultural importance, the seed being sold as a cereal under the same name. 



STARCH OF ARRHENATHERUM ELATIUS VAR. (Plato 3, figs. 17 and IS. Chart 21.) 



Histological Characteristics. In form the grains are usuallj' simple, l.)ut there are manj- aggre- 

 gates consisting of from two to many components. Pressure facets are well markeil on the separated 

 grains. The conspicuous forms of the aggregates which characterize this starch are round, oval, 

 and ovoid, and resemble those of Arena, l)ut arc of smaller size. The conspicuous forms of the simple 

 gi'ains which consist of the "filling-in grains" (Fiillstarke, Tschirch) and the separated-grains are 

 usually polj'gonal, but there are a few round, oval, ovoid, and dome-shaped. These gi-ains resemble 

 those of Avena, but there are more separated-grains, and these are more crystalline in appearance 

 because of the more marked angularities caused by the pressure facets. 



The hilum may be found as a round central spot, but generally there is either a cavity or cleft 

 at the position of the hilum. From the cavity small radiating fissures occasionally emerge. 



No lamcllce can he seen. 



The simple grains vary in size from the smaller, which are 2 liy 2n, to the larger, which are 14 

 by \2n. The common size of the isolated grains is 8 bj' 8/i. The aggregates are as large as 18 by lOyu. 



Polariscopic Properties. The figure appears usually to be centric. In grains in which the figure 

 can be distinguished the lines are rather thick and mostly straight. The majority of the grains are 

 so small and the polarization so low that it is impossible to satisfactorily determine the details of 

 the figure, but as far as can be determined the figure and lines are about the same as in Avena. 



The degree of polarization is low to fair and varies in a majority of the grains in the same aspect 

 of the grain. On the whole it is low. In the large grains it may be almost or entirely absent. 



With selenite the quach-ants are sometimes fairly well defined, and in the majority in which 

 they can be distinguished they are slightly unequal in size and irregular in shape. The blue is gen- 

 erall}- pure, but the yellow not quite pure. The colors appear to be purer in a larger proportion 

 of grains than in Avena. 

 26 



