450 



STARCHES OP AROIDE^. 



The degree of polarization is fair. Near some of the facets the grains appear isotropic, which 

 is probably due to the depressions. It is higher when the grain is seen on end, and also in the 

 larger grains. 



With selenite the quadrants are well defined, regular in shape, usually equal or nearly equal 

 in size. The colors are not quite pure. 



Iodine Reactions. — ^With 0.25 per cent Lugol's solution the grains color immediately and deeply 

 a blue-violet; with 0.125 per cent solution they tint immediately, the color deepening quickly until 

 fairly dark. The tint of these grains is more blue than that of the grains of R. africana and R. 

 alho-maculata. After heating the preparation until all the grains are completely gelatinized, the 

 solution is colored somewhat and the grains in varying degrees upon the addition of iodine. With 

 a slight excess of iodine the grains previously uncolored 

 assume a pink-violet color. After boiling 2 minutes, the 

 solution is colored more deeply, but the grain-residues 

 much less than the solution, on the addition of iodine. 

 With a slight excess of iodine the capsules are colored a 

 pink-violet and many are much crumpled and folded, 

 some disintegrated. 



Staining Reactions. — With gentian violet and with 

 safranin staining begins in about 30 seconds, the stain 

 deepens very slowly, and in 30 minutes it is light. 



Temperature Reaction.- — The temperature of gelatini- 

 zation is 75° to 77° C, mean 76°. 



Effects of Various Reagents. — With chloral hydrate- 

 iodine the reaction begins in 30 seconds and is over in 20 

 minutes. The hilum becomes prominent as a dark spot 

 or bubble, and the lamellae are visible. The periphery 

 often clears and becomes darker, while the inner part 

 appears light and opaque. Small grains darken finally 

 from the margin inward, the hilum swells, and the grain 

 is slightly swollen, not much distorted, and uniformly 

 dark, except in the center, where a large light space represents the swollen hilum. Larger grains 

 swell slightly in one or two places on the periphery, often at the corners of the facets. Gelatiniza- 

 tion proceeds over the whole grain, spreading along the margin on each side more rapidly than on 

 the central part. The gelatinized grains are not very large and show a dark, thin, marginal band 

 inclosing a large, light, clear space. Sometimes they are somewhat distorted. 



Reaction with chromic acid begins in 30 seconds and is over in 5 minutes. The hilum becomes 

 more prominent, and also some of the lamellse. Fine striae appear which radiate from the hilum 

 and become more and more prominent. The hilum swells and the imgelatinized portions of the 

 grain form a marginal ring of two layers, the inner being composed of large granules, and the outer 

 of a finely striated ring composed of indistinct, alternate refractive and non-refractive bands. The 

 grain continues to swell, and the ring or capsule gets thinner, clearer, and homogeneous-looking, 

 until finally one point swells out and is dissolved, allowing the semifluid contents to escape. The 

 remainder of the capsule then dissolves. 



The reaction with pyrogallic acid begins in 2 minutes. After an hour about half of the grains 

 are affected, but only half of these are entirely gelatinized. The hilum is prominent, and the lamellae 

 become less indistinct. There appear to be two methods of gelatinization. One by division of the 

 grain into several pieces by fissures extending from one side to the other in irregular directions, 

 and the independent gelatinization of these separate parts. This method produces a large, irregular, 

 folded and sacculated capsule. The other method is by dissolution of the inner part of the grain, 

 the swelling of the hilum, the appearance of fine striae which gradually become more distinct, and 

 the movement of the ungelatinized starch to the margin to form a ring consisting of two layers, 

 the inner granular layer being small, as in the Arum starches. The gelatinized grains are fairly 

 large and not much distorted, folded, or crumpled. 



The reaction with ferric chloride begins in 2 minutes and is over in 35 minutes. The hilum and 

 lamellae are rendered quite distinct. The outer portions of the grains become clearer and darker. 

 There is often gelatinization with protrusion at the corners and at the lines of union of the facets. 



Curve of Reaction'Intensities of Starch of 

 Richardia elliotiana. 



