GENERA CYPELLA AND MABICA. 



763 



There is a reaction with Purdy's solution in some grains in 3 minutes; some grains are unaffected, 

 Bome are only partially gelatinized, but nearly all are completely gelatinized in IJ^ hours. This 

 reaction is the same qualitatively as that to pyrogallic acid. 



PS CI PA 

 ~ PC PS 



GENUS MARICA. 



This is a tropical American genus of 11 species, stated to be more closely allied to Cypella than to 

 any other genus of the Iridacem. The starch from M. gracilis Herb, was studied as a type of the genua. 



STARCH OF MARICA GRACILIS. (Plate 76, figs. 451 and 452. Chart 294.) 



Histological Characteristics. — In form the grains are simple and isolated. There are a few 

 clumps. Pressure facets are not seen on any grains. The surface is smooth, but the margin is irreg- 

 ular, owing to irregularities in the development of the surface, especially the margin at the proximal 

 end. The conspicuous form is the reniform, the concave edge corresponding to the proximal end. 

 This concavity is sometimes marked with a protuberance; sometimes this end is straight or curved 

 outward, with or without a protuberance. There is quite a variety of forms ranging from rod- 

 like to elliptical, oval and ovoid, oval with pointed ends, sugar-loaf, pyriform, etc. The grains are 

 flattened and about one-third as thick as broad. On end or edge they are of a flattened elliptical 

 form. 



The hilum is not distinct and is a small round spot, eccentric one-sixth to one-ninth of the longi- 

 tudinal axis of the grain and in or to one side of the median line. It is sometimes fissured, and the 

 fissure is single in the longitudinal or diagonal axis, short or long, narrow and clean-cut. 



The lamelloe are fairly distinct, regular, fine, probably arcs of circles, which follow the outline 

 of the margin of the distal end; not so fine, but more dis- 

 tinct near the distal end. They do not vary much in 

 different grains. There are 16 to 18 on the larger grains. 



The grains vary in size from 5 to 52/i. The common 

 size is 39ii. 



Polariscopic Properties. — The figure is eccentric and 

 usually very obscure unless the grain is viewed on end or 

 edge, in which cases it is both distinct and clear-cut, and 

 the hnes are not bent nor otherwise distorted. Ordi- 

 narily its lines are very broad and diffused and merge 

 into one another. 



The degree of polarization is very low. It is usually 

 absent over the greater part of the surface, especially cen- 

 trally. When the grain is viewed on end or edge polar- 

 ization is high. 



With selenite the quadrants are usually fused. The 

 colors are impure. If the grain is on end or edge, the 

 quadrants are well defined, fairly regular in shape, and 

 unequal in size. The colors are not pure. 



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

 tion the grains color lightly at first and the color deepens slowly until it is a fairly deep indigo; with 

 0.125 per cent solution they begin to color faintly in about 1^ minutes, but the color deepens but 

 little. After heating in water until the grains are completely gelatinized, the solution colors deeply 

 and the grains fairly deeply on the addition of iodine. After heating for 2 minutes, the solution 

 colors very deeply and the grain-residues lightly. With an excess of iodine the capsules all color violet. 



Staining Reactions. — With gentian violet and with safranin the grains begin to stain at once 

 and in 30 minutes they are lightly stained, one as much as another. 



Temperature Reaction. — The temperature of gelatinization is 69° to 71° C, mean 70°. 



Effects of Various Reagents. — ^With chloral hydrate-dodine the reaction begins in some grains in 

 2 minutes and in many in 3 minutes. It is over in four-fifths of the grains in 20 minutes and in all 

 in IJ^ hours. The reaction usually begins with darkening and swelling of the margin at the distal 

 end and extends around the margin to the projections marking the extremities of the proximal end. 

 The reaction then progresses inward and upward over the grain until it is all darkened and some- 



MINUTES 

 Curve of Reaction- Intensities of Starch of Marica gracilis. 



