442 



STARCHES OF AROIDEiS}. 



starches. The most conspicuous forms are the si)herical and the ovoid, with one or more small, 

 not very clearly defined facets; dome-shaped and hemispherical grains, with one, two, or three 

 facets, or quite typically three at the base grouped triangularly about a common center. Polyg- 

 onal forms are not uncommon, especially among the smaller grains, which usually are irregular 

 in shape, owing to the differences in size, number, and position of the facets. 



The hitum is a fairly distinct, round, non-refractive spot, eccentrically or nearly centrally 

 placed. It is very rarely fissured, and if so the fissures are not deep or broad, and may be single 

 lines placed transversely or diagonally, or consist of three lines variously arranged. 



The lameUae are very distinct, regular, concentric rings, which may or may not follow the outline 

 of the margin; they follow it if the grain is of the dome-shaped type and the facets large. Some show 

 an irregularity of outline which does not seem to depend on the form of the grain. Two are usually 

 more distinct than the others, one rather near the hilum 

 appears to outline a definite area about the hilum, and 

 the other is about midway between this and the periphery. 

 The number of the lamellae varies between 10 and 16. 



The grains vary in size from 2 to 24/i. The common 

 size is 15^. 



Polariscopic Properties. — The figure is clear-cut, dis- 

 tinct, and regular in shape, usually slightly eccentric. 

 The lines are generally of the same size and distinctness 

 throughout their length. The figure is sometimes ren- 

 dered peculiar by the facets, so that one line may appear 

 to have two branches, etc. Lines indicating the posi- 

 tions of lamellae could be distinguished on one or two of 

 the larger grains. The figure is typically in the form 

 of a cross. 



The degree of polarization is fairly high . Inasmuch as 

 the grains are of or closely approach the spherical form, 

 there is not much variation according to the aspect viewed. 

 Owing to the fact that there are concavities in the faceted 

 surfaces, polarization is often low at these points. 



With selenite the quadrants are well defined and usually of nearly the same shape and size. 

 The colors are quite pure. 



Iodine Reactions. — With 0.25 per cent I^ugol's solution the grains color at once and quite deeply. 

 With 0.125 per cent solution they tint lightly at once, but the color deepens quickly. This starch 

 is the most sensitive to iodine of the Arum starches. After heating the solution until the grains 

 are completely gelatinized, the solution is colored slightly and some of the grains deeply and others 

 lightly on the addition of iodine. Some of the colored capsules or portions of capsules are colored 

 violet on adding more iodine. After boiling 2 minutes, the solution colors more deeply, but the 

 grain-residues less deeply and some not at all, many being reduced to mere granular masses. All 

 the uncolored capsules or portions of capsules are colored violet with a slight excess of iodine. 



Staining Reactions. — With gentian violet the grains begin to stain in 2 minutes and after 30 

 minutes are stained fairly deeply to deeply. 



With safranin the grains begin to stain in a minute, but at the end of 30 minutes are stained 

 fairly deeply. 



Temperature Reaction. — The temperature of gelatinization is 69.5° to 70.5° C, mean 70°. 



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

 and all the grains are darkened and the reaction is practically over in 5 minutes. The hilum is often 

 prominent as a dark spot. The lamelhe are not obscured. The grain is colored violet; then the mar- 

 gin begins to darken, especially about the corners of the facets, from here it spreads all around the 

 margin, and then inward until the whole grain is dark. This is accompanied by very little and very 

 gradual swelling. Quite commonly some of the marginal starch is gelatinized and protrudes, a 

 reaction that appears to be characteristic of this species as compared with the other Arums. The 

 capsules are imiformly dark, except for the lighter swollen hilum, and are not large or much distorted. 



The reaction with chromic acid begins in 30 seconds and is over in 6 minutes. The hilum and 

 lamella; become prominent; fine striae appear first about the hilum and then radiate throughout 



Curve of Reaction-Intenaitiesof Starch of Arum 

 cornutum. 



