GENUS RICHARDIA. 



451 



PA FC P S CI PA CA 

 POPS 



and this may extend over a great part of the grain, followed by a swelling of the grain as a whole. 

 Other grains swell by the dissolution and swelling of the less resistant starch of the inner part of 

 the grain. The ungelatinized portions are pushed to the margin to form a homogeneous, one-layered 

 ring, which does not show granules, bands, or fine striae. This ring becomes in time clearer and 

 thinner as the grain swells and forms a gelatinized capsule. The gelatinized grains are large and 

 not much distorted, though there is sometimes an invagination or depression in the capsule. 



With Purdifs solution the reaction begins with a few of the smaller grains in IJ/^ minutes, but 

 after an hour there is no further reaction. The hilum and lamellse are prominent. The lamella are 

 not rendered so prominent as with pyrogallic acid, which is unusual. Some of the grains gelatinize 

 quickly, with swelling of the hilum and the formation of a marginal ring, which rapidly becomes 

 thin and homogeneous. Other grains are split by irregular fissures into several pieces, which gelat- 

 inize independently. This reaction is not completed in all the grains in which gelatinization begins. 



STARCH OF RICHARDIA AFRICANA. (Plate 16, fig. 93. Chart 82.) 



Histological Characteristics. — In form the grains are simple and isolated, except a few that 

 occur in aggregates ; they have from one to six or seven pressure facets, which are unequal in size 

 and shape and irregular in their positions in different grains; some grains are entirely covered with 

 facets. The polygonal forms are the most common and vary considerably in shape, owing to vari- 

 ations in number, size, and distribution of the facets; occasionally spherical, dome-shaped, hemi- 

 spherical, triangular, ovoid (with one end flattened), and 



irregularly elliptical forms are seen (the irregularities Chart No. 82. 



being caused by irregular facets). Many grains, because 

 of their marked angularities, have the appearance of 

 crystals. 



The hilum is usually not visible. In several grains it 

 appeared as a very small, non-refractive, round spot, 

 centrically or slightly centrically placed. It was in no 

 instance fissured. 



The lamellce can not be distinguished. 



The grains vary in size from 1 to 10/i. The common 

 size is Gfi. 



Polariscopic Properties. — The grains are so small and 

 the polarization so very low (almost nil), that it is im- 

 possible to determine anything satisfactory with regard 

 to the figure or to the reactions with selenite. 



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

 tion the grains color a deep blue-violet somewhat less 

 deeply than li. elliotiana; with 0.125 per cent solution 

 they tint readily and the color deepens quickly. The 

 shade is the same or slightly lighter than in R. elliotiana, but the color is more of a reddish-violet. 

 After heating until the grains are completely gelatinized, the solution is fairly colored and the gelat- 

 inized grains very little on the addition of iodine. Most of the grains show a reddish-violet capsule 

 on adding a very slight excess of iodine. After boiling 2 minutes the solution is colored deeply, but 

 the grain-residues less deeply. Very few grain-residues contain any blue-reacting starch and all 

 have reddish-violet capsules. 



Staining Reactions. — With gentian violet and with safranin the grains begin to stain within a 

 minute, and after 30 minutes they are lightly colored, rather less so than R. elliotiana. 



Temperature Reaction. — The temperature of gelatinization is 74° to 76° C, mean 75°. 



Effects of Various Reagents. — With chloral hydrate-iodine the reaction begins in 45 seconds 

 and is over in 5 minutes. The hilum is occasionally more prominent. The lamella; are visible. 

 The corners of the facets darken and begin to swell, and the processes usually extend entirely around 

 the margin and then inward. The grains do not swell as a whole until the hilum is affected by the 

 reaction. The gelatinized grains are not very large and they have a dark marginal ring surrounding 

 a lighter center. There is some protrusion at the corners of the facets, otherwise no distortion. 



Reaction with chromic add begins in IJ^ minutes and is completed in 4 minutes. The hilum 

 becordes more visible in many grains. Fissures frequently extend inward from the margin before the 



Curve of Rcaction-lntennities of Starch of 

 Richardia africana. 



