362 



STARCHES OF GRAMINACE^. 

 NOTES ON THE STARCHES OF ANDROPOGON. 



The starches of the three forms of Andropogo?i are so alike in their gi'oss histological characters 

 that ciiffcroiitiation by this means is not possible. They arc also very much alike in their polariza- 

 tion, iodine, and aniline reactions, the differences being within the limits of error of experiment. 

 In the temperature of gelatinization they show distinct differences, the order being, shallu (66.9 C), 

 White Kafhr corn (68 C), and Yellow Branching sorghum (70 C). In the chemical reactions there 

 arc only minor differences, and such as to suggest very closely related botanical forms. 



GENUS PANICUM. 



Panicum is an immense genus of grasses, comprising al)out 300 species that are world-wide in 

 distribution, Ijut especially abundant in the tro])ics. The specimen studied as a tj'pe of the genus 

 is the cultivated form of Panicum crus-galli Linn., known as the Japanese or barnyard millet. 



STARCH OF PANICUM CRUS-GALLI VAR. (JAPANESE OR BARNYARD MILLET). 



(Plate 1, figs. 5 and 6. Chart 13.) 



Histological Characteristics. In form the grains are simple ami occur isolated, excejiting a few 

 in aggregates which consist of two or more comjionents. The conspicuous forms are polygonal and 

 spherical, the former predominating. 



A cavity is usually found at the hilum, and sometimes radial fissures pass out from it. 



The lamcllcB are not visible. 



The grains vary in size from the smaller, which are 1..5 by 1.5yu, to the larger, which are 10 by 

 IOai. The common size is l/i. 



Polariscopic Properties. The figure is usually centric, Init owing to the smallness of the grain 

 is oliscure. The lines of the figure appear to be fairly thick and are generally straight and some- 

 times bisected. 



The degree of polarization is low to fair. In some grains there is a variation in the same aspect 

 of the same grain. 



With selenile the quadrants are distinct, and in some grains are equal in size and regular in 

 form. They are so minute that it is impossible to state the peculiarities with accuracy in the ma- 

 jority of the grains. The blue and yellow colors vary in brightness and purity, the blue being 

 less bright than the yellow. The yellow is generally not 

 quite pure, but the blue appears to be pure. 



Iodine Reactions. With a 0.2.5 per cent Lugol's so- 

 lution most of the grains color a light violet at once, and 

 the color deepens rather slowly; with a 0.125 per cent 

 solution they do not color immediately, but gradually 

 assume a very light violet tint, some grains staining 

 more deeply than others. After heating in water until all 

 the grains are completely gelatinized, the solution be- 

 comes a light bluish-violet, and the majority of the grains 

 color a deep blue, while others have a reddish tint. After 

 boiling for 2 minutes the solution colors very deeply on 

 the addition of iodine, but most of the gelatinized grain- 

 residues are not colored. With an excess of iodine, the 

 capsules become an old-rose to a wine-red tint. 



Staining Reactions. With gentian violet the grains 

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

 they are but lightly stained. 



With safranin the grains begin to stain very lightly 

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



Temperature Reaction. The temj^erature of gelatinization is 74.5 to 76 C, mean 75.25. 



Effects of Various Reagents. With chloral hydrate-iodine the reaction begins in most of the 

 grains in 30 seconds to a minute, and is over in nearly all of the grains in 15 minutes. The reac- 

 tion begins at the corners and angles of the facets and the starch at these points darkens and swells 

 slightly, and the process spreads inward over the whole grain. The marginal starch is affected 



PS CI PA I 

 PC PS 



Curve of Reaction-Intensities of Starch of Panicum crus- 

 galli var. (Japanese or Barnyard Millet). 



