GENUS ANDROPOGON. 



359 



With Purdy's solution the n-action, which consists in a little gclatinization aliout the hilum, 

 begins in some grains in a minute, but the change does not proceed much farther even at the end of 

 an hour. 



STARCH OF ANDROPOGON SORGHUM VAR. (YELLOW BRANCHING SORGHUM). 



(Plate 1, figs. 3 and 4. Chart 11.) 



Histological Characteristics. — In form both simple and compound grains are present, almost 

 solely the former. There are a few aggregates. Some of the grains have pressure facets. The con- 

 spicuous forms of the simple grains are polygonal, round, and rounded oval. The isolated grains 

 are often dome-shaped or sugar-loaf-shaped. The aggregates frequently consist of one large grain 

 and one minute grain. The grains very closely resemble those of White Kaffir sorghum. 



The hilu7n is a clear, rather refractive spot, which is centric in the round grains and slightly 

 eccentric in some of the oval and polygonal forms. There may be more than one hilum without 

 lines of separation. Sometimes three arc arranged at the angles of an imaginary triangle. Deep 

 clefts are usually foimd at the hilum, frequently ragged in character, and usually in the form 

 of a Y or diagonal cross. If but one cleft is found it is more often either slightly arched or 

 diagonally placed. The arrangements of the clefts are very similar to those noted in White Kaffir 

 sorghum. 



The lamella are not usually visible, and neither their structure nor number could be determined, 

 as was also the case with White Kaffir sorghum. 



The grains vary in size from the smaller, which are 2 by 2/i, to the larger, which are 22 by 24/x 

 in length and breadth. The common size is 16 by 16jtt. 



Polariscopic Properties. — The figure is usually centric, regular, and very distinct. The lines are 

 thick, commonly straight, and broadening towards the margin. There is a greater proportion of 

 figures with lines slightly bent than in White Kaffir corn. 



The degree of polarization is high, occasionally vary- 

 ing slightly in the same aspect of a grain. It is a very 

 little higher than in White Kaffir corn. 



With selenite the quadrants are well defined, and 

 usually unequal in size and irregular in shape. The colors 

 are pure. There is a greater variation among the quad- 

 rants as to size and shape than in White Kaffir corn. 



Iodine Reactions. — With a 0.25 per cent Lugol's solu- 

 tion all the grains color a fairly deep violet; with a 0.125 

 per cent solution they all color lightly, but the shade does 

 not dee])en rapidly. It is slightly less than that of the 

 grains of White Kaffir corn. After heating in water until 

 all the grains are completely gelatinized the solution colors 

 lightly and the gelatinized grains very deeply on the ad- 

 dition of iodine. After boiling for 2 minutes the solution 

 colors very deeply, but the gelatinized grain-residues not 

 at all. The capsules all color red or violet with an excess 

 of iodine. 



Staining Reactions. — With gentian violet the grains 

 begin to stain at once. In 30 minutes they are lightly stained, some more than others. The 

 staining is slightly less than that of the grains of White Kaffir corn. 



With safranin the grains begin to stain at once; in 30 minutes they are lightly stained, some 

 more than others. The staining is slightly less than that of the grains of White Kaffir corn. 



Temperature Reaction.— The temperature of gclatinization is 69.1° to 70.8° C, mean 69.95°. 



Effects of Various Reagents.— With, chloral hydrate-dodine the reaction begins in most of the 

 grains in 30 seconds. It is complete in nearly all in 10 minutes, and in all in 15 minutes. It is the 

 same qualitatively as that of the grains of White Kaffir com. 



The reaction with chromic add begins in some grains in 20 seconds and in all in 45 seconds, 

 and is over in 4 minutes. It is the same qualitatively as that of the grains of White Kaffircom. 



With pyrogallic add the reaction begins in 30 seconds and is over in 3}4 minutes. It is the 

 same qualitatively as that of the grains of White Kafl&r corn. 

 25 



Curve of Reaction-Intensities of Starch of Andropogon 

 sorghum var. (Yellow Branching Sorghum). 



