710 



STARCHES OF IRIDACEiB. 



PS CI PA CA 

 ~ PC PS 



STARCH OF HOMERIA COLLINA. (Plate 67, figs. 401 and 402. Chart 269.) 



Histological Characteristics. — In form the grains are usually simple, with occasional compound 

 grains consisting of two components. There are some clumps. The smaller grains often form 

 doublets or triplets linearly arranged, and there is a tendency for small grains to adhere to the large 

 grain. The smaller grains are also very variable in form, some are narrow, but most of them are 

 more or less markedly irregular in outline. Pressure facets on the single grains are rare. The sur- 

 face is usually very irregular, owing to uneven amorphous accretions on the surface and to irregu- 

 larities in development of the primary grains. Nodular projections are not uncommon. The con- 

 spicuous forms are the elongated ovoid, lenticular, reniform, pure ovoid, triangular with marked 

 corners, womb-shaped, and irregularly quadrilateral or polyhedral with rounded corners; also a 

 few pyriform. The grains are not flattened in any diameter. 



The hilum is eccentric and quite distinct. It may be in or to one side of the median line, and 

 when not fissured it is a comparatively large round spot. There may be 2 hila. It is very often 

 fissured, but the fissure is not especially deep or wide, 

 and usually is irregular or ragged. It sometimes appears 

 as though there had been originally two fissures which 

 started from two centers and later coalesced. 



The lamellce are not distinct. When they could be 

 seen they appeared to be coarse, irregular, continuous 

 rings or segments of rings. They are often irregular, but 

 do not follow the irregularities of the margin of the grain. 

 Usually one very distinct lamella outlines a smooth, non- 

 lamellated space surrounding the hilum. There are about 

 6 to 8 lamellae on a medium-sized grain. 



The grains vary in size from 2 to 42fi. The common 

 size is 28/1. The elongated ovoid and lenticular grains 

 have average dimensions of 38 by 20m, and the quadri- 

 lateral about 36 by 30/i in length and breadth. There is 

 a larger proportion of small grains in this starch in com- 

 parison with the number found in starches generally. 



Polariscopic Properties. — The figure is eccentric, and 

 is, as a rule, clear-cut and distinct. The lines in some of 

 the larger grains are bent and otherwise distorted, with 

 here and there peculiar duplications of parts of the figure, owing probably to the amorphous con- 

 cretions on the surface. The central part of the figure is sometimes a large, irregular, dark spot. 



The degree of polarization is high. It varies in different parts of the same grain and also in 

 different grains. 



With selenite the quadrants are, as a rule, clear-cut and well defined, often very irregular in 

 shape and unequal in size. The colors are pure in most grains. 



Iodine Reactions. — With 0.25 per cent Lugol's solution the grains are colored deeply at once; 

 with 0.125 per cent solution they tint deeply, almost as deep as that with a 0.25 per cent solution. 

 After heating until the grains are completely gelatinized, the solution is colored deeply and the swollen 

 grains very deeply on the addition of iodine. Some of the grains which color less deeply than 

 others exhibit a violet-colored capsule when an excess of iodine is used. After boiling for 2 minutes 

 the solution is colored very deeply, but the grain-residues less deeply. Most of the capsules retain 

 Bome blue-reacting starch. With an excess of iodine all the capsules are of a red-violet color. 



Staining Reactions. — With gentian violet in 15 minutes the grains show some slight stain and 

 in 30 minutes the color is very little deeper. The color is deeper than in Morcea tristis. 



With safranin there is a slight coloration in 7 minutes, but in 30 minutes the tint is very little 

 deeper than at first. The stain is deeper, however, than that with gentian violet and deeper than 

 in M. tristis. 



Temperature Reaction. — The temperature of gelatinization is 72° to 73° C, mean 72.5°. 



Effects of Various Reagents. — With chloral hydrate-iodine some grains show a reaction in 10 

 minutes. Most of the smaller grains are gelatinized in 20 minutes, but at this time most of the 

 larger grains are unaffected. A few of the larger grains are gelatinized in 45 minutes, and about 



Curve of Reaction-Intensities of Starch of Homeria 

 collina. 



