GENUS PREESIA, 



737 



conspicuous form is the hemispherical with one, two, or three facets at the base; also spherical to 

 almost spherical, ovoid, and polygonal, a few of the latter having small facets all over the surface. 

 The grains are not flattened and appear spherical when viewed on end. 



The hilum is usually centric and a fairly distinct, relatively large, non-refractive spot, always 

 in the median line. Rarely the hilum is fissured, and if so the fissuration is either in the form of a 

 cross or a 3-armed figiu-e. Double hila may be seen in a single grain, and 2 or more may be observed 

 in aggregates. 



The lamelloe are rather indistinct, regular, fine, concentric rings, following the shape of the 

 margin of the grain, even when near the hilum. When the lamella; were distinct enough to be 

 counted it was estimated that the number was about 10 to 12 on a medium-sized grain. They 

 become more distinct near the margin and one situated 

 midway between the hilum and the margin was promi- 

 nent in most of the grains. 



The grains vary in size from 2 to 18/i. The com- 

 mon size is 12/i. 



Polariscopic Properties. The figure is usually cen- 

 tric. It is distinct and fairly clear-cut, but the lines are 

 somewhat wider at the margin and are sometimes bent 

 or otherwise distorted. 



The degree of polarization is fairly high. It varies 

 somewhat in different grains and in the same aspect of 

 a given grain. It is higher at the proximal than the 

 distal end. 



With selenite the quadrants are sharply defined, 

 fairly regular in shape, but unequal in size. The colors 

 are fairly pure. 



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

 tion the grains color deeply a blue- violet; with 0.125 per 

 cent solution they tint slightly. After heating in water 

 until the grains are completely gelatinized, the solution is 

 colored a deep indigo and the grains lightly to deeply, or not at all, upon the addition of iodine. 

 The gelatinized grains are folded and distorted, but do not lose all of their original shape. After 

 boiling for 2 minutes the solution colors more deeply and the grain-residues much less deeply. 

 With an excess of iodine the capsule stains violet. 



Staining Reactions. With gentian violet the grains begin to stain in 3 minutes and after 30 

 minutes are fairly stained. 



With safranin the grains begin to stain in a minute and in 30 minutes are lightly stained. 



Temperature Reaction. The temperature of gelatinization is 76 to 77.5 C, mean 76.75. 



Effects of Various Reagents. With chloral hydrate-iodine reaction begins in 30 seconds in the 

 smaller grains and is general in 2 minutes. The reaction is over in three-fourths of the grains in 

 30 minutes, but the reaction is incomplete in an hour. The hilum becomes much more distinct 

 as a dark spot and the whole grain is colored a light violet. Two lines or fissures often appear in 

 the hemispherical forms which run from the hilum to the corners of the facets. The margin becomes 

 dark at one or two points, generally at the sharp corners of the facets, and there may be slight 

 protrusion from these points. Then the reaction spreads upward and inward over the whole grain, 

 and when it reaches the hilum this part swells, accompanied by swelling of the whole grain. The 

 gelatinized grains do not become very large and do not lose their original contour. They have 

 usually a dark indigo-colored, marginal ring surrounding a lighter, round, central space. 



The reaction with chromic acid begins in a minute and is over in 4 minutes. The hilum 

 becomes very distinct and a line extends from it on each side to the corners of the facet at the 

 base of the grain. The hilum swells, and these lines open out to form a triangular space which 

 divides the grain into two portions, the inner becoming coarsely granular, and the outer or mar- 

 ginal becoming finely striated and marked with two or three refractive and non-refractive rings. 

 One corner of the marginal ring now dissolves and opens out, allowing the coarsely granular inner 

 portion to flow out. The exuded starch passes into solution, followed by solution of the more 

 resistant marginal part. 



Curve of Reaction'Intensities of Starch of Freesia 

 refracta var. alba. 



