GENUS ARUM. 443 



the grain, becoming more and more distinct, and the hilum is seen to swell. A clear inner space 



develops, which increases in size. The swelling is communicated to the entire grain, and the strife 

 open wider and become more distinct, and a band of two layers is formed at the margin of the large, 

 clear, inner space. The inner layer of the band appears to be composed of one or two layers of 

 granules formed by the widely separated striie. The outer layer is more compact and presents 

 the appearance of two or three alternate refractive and non-refractive layers crossed radially by 

 fine stria;. The layers are very distinct in this starch. The grain continues to swell from the inside, 

 the margin becomes thinner, clearer, and quite homogeneous. One part of the capsule protrudes 

 and dissolves, permitting the contents of the capsule to stream out and be dissolved. The other 

 parts of the capsule pass into solution slowly. 



Reaction with pyrogalUc acid begins in 30 seconds. After 30 minutes all the grains are affected 

 and nearly all are fully gelatinized. In the reaction the hilum and lamellie become prominent, fine 

 stria; appear which radiate from the hilum, the hilum swells, the inner starch is converted into a 

 gelatinous mass, and the more resistant marginal starch is formed into a band of two layers, the inner 

 granular, the outer striated, but not so plainly marked by the refractive and non-refractive bands as 

 in the reaction with chromic acid. This marginal starch, as the grain continues to swell, becomes 

 smaller, clearer, and quite homogeneous. The gelatinized grains are fairly large and not much dis- 

 torted, crumpled, or folded. 



With ferric chloride reaction begins in a minute and is over in 12 minutes. The hilum becomes 

 very prominent as a dark spot or bubble. Some of the coarser and more distinct lamellae appear 

 more clearly. The margin of the grain becomes clearer and darker, while the inner portion appears 

 lighter and more opaque. In some of the more quickly reacting grains this clear appearance spreads 

 over the whole grain, there is a little swelling, and the inner portion dissolves quickly; the 

 margin is distinct, but very light and homogeneous. In the more slowly reacting grains the grain 

 becomes divided by fine stria; and the inner portion dissolves and swells, causing general swelling. 

 The undissolved portion at the margin forms a very broad, distinct ring marked with fine stria; 

 and refractive and non-refractive bands. Only in the less sensitive grains can preliminary gelatin- 

 ization of the margin be seen. A bubble forms at the hilum in some cases which gradually disappears 

 as the grain swells. As the grains continue to enlarge the margin becomes thinner, lighter, and quite 

 homogeneous, and invagination of one portion will often take place. The gelatinized grains are 

 large and somewhat distorted by invagination, and are not much folded and crumpled, but retain 

 much of the original shape of the grain. 



The reaction with Purdy's solution begins very slightly in 30 seconds and is over in 15 minutes, 

 about half of the grains being affected. The hilum and lamella;, especially the latter, become very 

 prominent. The hilum swells slightly and fine striae appear which radiate from the hilum. As 

 the hilum swells, the striae become more distinct and concentric fissures appear in the lines of the 

 more prominent lamellae, thus forming apparently concentric rows of granules; while out towards 

 the margin there is the usual appearance of fine striae and refractive and non-refractive bands. 

 As the grain continues to swell, this margin becomes thinner and homogeneous, until finally it is a 

 thin, non-refractive line. The gelatinized grains are fairly large, and while some invagination may 

 occur, especially at the faceted surfaces, they are not much crumpled or folded or otherwise distorted. 



STARCH OF ARUM ITALICUM. (Plate 14, figs. 81 and 82. Chart 78.) 



Histological Characteristics. — In form the grains are simple and for the most part isolated. 

 They occur in part in small clumps or pseudo-aggregates, rarely in aggregates. The grains are 

 usually marked with one or more pressure facets, usually very sharply defined and situated at the 

 distal end of the grain. Facets may be on the sides also, but there is always some portion of the 

 outside not so marked. There may be from one to five or six on a grain, and the presence of three 

 at the distal end is not uncommon. The most conspicuous forms are the dome-shaped and hemi- 

 spherical (marked by two or three facets), triangular, and spherical. There are a few quadrangular 

 and irregularly polj^gonal forms, and some ovoid grains. They vary in shape according to the 

 aspect viewed, because of differences in size, form, number, and position of the pressure facets. 



The hilum is not distinct; it is a comparatively large round spot, usually very slightly eccen- 

 trically placed and always in or near the median line; lines extend on each side, continuing to the 

 edges of the facets. The hilum is rarely distinctly fissured, and if so the fissure is generally regular, 

 clean-cut, single, 3-armed, or stellate. There are no multiple hila. 



