712 



STARCHES OF IRIDACE^. 



and distal end. They are quite regular and from the equator to the distal margin follow the outline 

 of the grain. The number can not be accurately determined. 



The grains vary in size; the smaller are 5 by 5m; the larger are 30 by 40^ in length and breadth. 

 The common sizes are 20 by 30^ in length and breadth, and 24 by 26yu in length and breadth. 



Polar iscopic Properties. The figure is eccentric and usually obscure. A large portion of the central 

 part of the grain is entirely dark, so that in most grains onlj- the outer parts of the quadrants are illumi- 

 nated. In the few grains in which the figure is clearly defined the lines are broad, but usually not sharp. 



The degree of polarization varies from very low in most grains to fair in a few. It varies greatly 

 in different aspects of the same grain, being fairly high when the grain is viewed on end or edge. 

 In the broad aspect of a grain it is usually entirely lacking about the hilum, and a very large area, 

 almost the entire grain, may be absolutely dark. 



With selenite the quadrants are as a rule not defined; 

 they vary in shape and are unequal in size. The colors 

 are not pure. 



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

 tion the grains all begin to color a fairly deep indigo; with 

 0.125 per cent solution they all color fairly and the color 

 deepens gradually. After heating in water until the 

 grains are completely gelatinized, the solution colors 

 fairly and the gelatinized grains deeply on the addition 

 of iodine. After boiling for 2 minutes the solution colors 

 very deeply and the grain-residues hghtly. The capsules 

 all color a pale violet with an excess of iodine. 



Staining Reactions. With gentian violet and with 

 safranin the grains all begin to stain at once and in 30 

 minutes are rather lightly stained. 



Temperature Reaction. The temperature of gelatin- 

 ization is 60 to 62 C, mean 61. 



Effects of Various Reagents. With chloral hydrate- 

 iodine reaction begins in all in a minute. It is over in 

 four-fifths of the grains in 7 minutes and in all in 12 minutes. The margin at the distal end swells 

 slightly and becomes dark, and this process extends to the depressions at each side of the proximal 

 end and then moves upward and inward, later including the whole margin. The process spreads 

 centrally until it reaches the hilum. The fissures at the hilum usually widen greatly, and appear to 

 divide the starch which has not yet gelatinized into two or more pieces, and these gelatinize later. 

 The gelatinized grains are fairly large and of a uniform dark indigo, except for the light lines which 

 occupy the position of the lines of the figures. 



The reaction with chromic acid begins in a few seconds and is over in 50 seconds. The starch 

 about the hilum begins to be converted into a gelatinous mass, and rather coarse striae appear 

 throughout the grain. At the hilum a bubble forms which first increases and then decreases in size, 

 as the grain swells, and finally disappears. The whole interior of the grain now passes into a gelat- 

 inous mass, leaving only a thin capsule, and the grain swells greatly. The capsule is dissolved in 

 one or two places near the distal end, and the inner gelatinized starch flows out and is completely 

 dissolved, the capsule dissolving later. 



Reaction with pyrogallic add begins in a few seconds and is over in 55 seconds. It is so rapid 

 that the successive steps can not bo satisfactorily determined. The starch about the hilum gelat- 

 inizes, followed by gelatinization of the rest of the grain, except several bright refractive spots, 

 which remain in the neighborhood of the proximal end, but finally disappear. The gelatinized 

 grains are much distorted, folded, and sacculated, particularly at the distal end. Their appearance 

 suggests that most of the gelatinized contents had escaped into the surrounding liquid. 



Reaction with ferric chloride begins in a few grains in 45 seconds. It is over in nearly all in 

 15 minutes and in all in 25 minutes. The reaction begins at the distal end, which becomes slightly 

 fissured at two or three places, from which fissures there is a protrusion of gelatinous material in- 

 closed in the gelatinized capsule. This process continues until all of the distal end and also many 

 places on the margin are gelatinized. Then at two or three points on the proximal end the starch 

 swells out in short, finger-like projections. The process now moves inward until all the starch is 



Curve of Reaction-Intensities of Starch of Tigridta 

 pavonia var. grandiflora alba. 



