446 



STARCHES OP AROIDEiB. 



Chart No. 79. 



GENUS ARIS/EMA. 



About 60 species of tuberous, herbaceous plants constitute this genus. Among the best known 

 is A. triphyllum Torr., popularly known as the Jack-in-the-pulpit or Indian turnip. Starch was 

 obtained from this species. 



STARCH OF ARIS^MA TRIPHYLLUM. (Plate 14, figs. 83 and 84. Chart 79.) 



Histological Characteristics. — In form the grains are simple and mostly isolated, they rarely 

 occur in small aggregates and occasionally in clumps; all show pressure facets. The most conspic- 

 uous forms are the spherical and ovoid, marked with one or two small, rather poorly defined pres- 

 sure facets; dome-shaped; hemispherical and triangular, all with pressure facets. There are also 

 quadrangular and multiangular forms, the latter being uncommon. The dome-shaped and hemi- 

 spherical forms often have three or four facets at the base, grouped about a common center. The 

 facets on many grains are small and not definitely outlined; on others they are well defined and reg- 

 ular in shape. On end the grains usually appear round. The shape varies according to the position, 

 number, and size of the facets. 



The hilum is a very large, distinct, round, non-refractive spot, situated somewhat eccentric- 

 ally; commonly fissured, the fissure being neither deep nor wide and usually a single transverse 

 line; or there may be three lines arranged in an irregu- 

 larly stellate fashion. The hilum may be double, and 

 often appears to be in a well-defined area formed by one 

 very distinct lamella. 



The lamellm are very distinct, coarse, concentric 

 rings which follow the outline of the margin. One or two 

 are usually especially prominent, one outlining a space 

 about the hilum as before stated, and the other being 

 located about midway between the first and the margin 

 of the grain. In a few grains there appear to be two sets 

 of lamellae which have no connection with each other, one 

 consisting of a few very large, distinct lamellae about the 

 hilum, and the other of very fine indistinct lamellae sur- 

 rounding the first set. The lamellae number from 8 to 16. 



The grains vary in size from 3 to 28/i. The common 

 size is 14/i. 



Polariscopic Properties. — The^wre is usually slightly 

 eccentric, distinct, clear-cut, and in the form of a cross. 

 The lines are broad, ragged, and of the same distinctness 

 throughout their length, but may be broader near the 

 margin. The figure is modified in a pecuUar manner when the faceted end is seen, appearing as 

 though there were more than one figure or as if the lines had branched. 



The degree of polarization is fair. It is lower than that of Arum cornutum, but higher than in 

 A. palcestinum. It is lowest at the faceted ends and highest when the grain is seen on end, and it 

 also varies somewhat in different grains. 



With selenite the quadrants are well marked, generally equal in size, and commonly regular 

 in shape. The colors are fairly pure. 



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

 a blue-violet; with 0.125 per cent solution they tint lightly, but the color deepens quickly. The col- 

 oration is less than with A. palcestinum. After heating the grains until they are completely gelatin- 

 ized, the solution is not deeply colored on the addition of iodine, but the gelatinized grains color deeply. 

 The grains are not much distorted or crumpled. After boiling 2 minutes, the solution is deeply col- 

 ored, the grain-residues very little. With a slight excess of iodine the capsules become of a violet color. 



Staining Reactions. — With gentian violet the grains begin to stain in 30 seconds. At the end 

 of 30 minutes they are well stained. This starch stains the deepest of the four Arum starches studied. 



With safranin the grains begin to stain in 30 seconds, but at the end of 30 minutes they are 

 only fairly stained. 



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



Cunre of Reaction- In tens! ties of Starch of 

 Ariaeema triphyllum. 



