686 



STARCHES OF TACCACEiE. 



STARCHES OF TACCACEyE. 



Class, Monocotyledones. Order, Liliales. Family, Taccacese. Genus represented, Tacca. 



This family is closely allied to Amaryllidacew, and includes only the genera Taccn and Schizo- 

 capsa. Tacca is typical of the family, and comprises about 9 species; Schizocapsa is a monotypic 

 genus. 



GENUS TACCA. 



Tacca is a genus of tropical plants, some of which are cultivated for their rhizomes, which are 

 rich in starch, containing as much as 30 per cent. Of the 9 species, 2 are natives of tropical America, 

 and the others of Asia, Africa, the Indian Archipelago, and the Pacific Islands. The starch from 

 one source was studied, T. pinnatijida Jack. {T. oceanica Nutt.). The starch is commercially known 

 as Williams's arrow-root. South Sea arrow-root, and Fiji arrow-root. 



STARCH OF TACCA PINNATIFIDA. (Plate 62, figs. 371 and 372. Chart 254.) 



Histological Characteristics. Inform the grains are simple and almost isolated, with the exception 

 of a few which occur in aggregates that consist of two or rarely of three or more components. 

 Nearly all have one or more, commonly two, pressure facets. The surface is rounded and very 

 even, except near the pressure facets, where often the appearance of swelling suggests secondary 

 deposits or partial gelatinization. The conspicuous 

 forms are the dome-shaped with from one to three facets 

 at the base, spherical to oval, and polygonal. Some of 

 the dome-shaped type are more or less elongated, some- 

 times appearing like a half of a flattened ellipse. A 

 spherical grain may be seen with a single pressure facet. 

 In the aggregates consisting of two grains, the grains are 

 commonlj; unequal in size. The grains are not flattened, 

 and when seen from the proximal end appear spherical; 

 but from the distal end they appear circular and irregu- 

 lar on the top on account of the facets. 



The hihi7n when not fissured is a large, round, refrac- 

 tive spot, usually eccentric about two-fifths of its longi- 

 tudinal diameter and in the median line. It is generally 

 marked by a deep, transverse fissure, showing at times a 

 single and at others a double curve. It is often subdivided 

 by numerous fissures, and often there is a 3-armed figure, 

 and rarely a stellate arrangement of small fissures. 



The lamellcR are fairly distinct, relatively coarse, 

 widely spaced, regular, usually concentric rings. They 

 vary in size, spacing, and distinctness even in the same grain, those centrally located being the 

 coarser and more distinct than those near the margin. They are for the most part circular and 

 follow the outline of the margin only when very near it. There is an average of 10 to 14 lamellae 

 on medium-sized grains. 



The grains vary in size from 6 to 28/i. The common size is 18/i. 



Polariscopic Properties. The figure is usually eccentric, distinct, and clear-cut. The four 

 lines are distinctly visible throughout and tend to become somewhat broader or narrower towards 

 the margin of the grain, and are sometimes bent or otherwise distorted. Two hnes usually cross 

 the grain obliquely to the corners of the facets. 



The degree of polarization is high. It is higher from the end than from any other aspect of 

 the grain, but occasionally it is very low at the faceted end, due to the hollowed spaces of the facets. 

 It does not vary much in different grains. 



With selenite the quadrants are well defined, usually irregular in shape, and unequal in size. 

 The colors are fairly pure. 



Iodine Reactions. With 0.25 per cent Lugol's solution tlie grains color deeply a redchsh-blue; 

 with 0.125 per cent solution they are only slightly colored at first, but deepen rapidly. After heat- 



Curve of Reaction-Intensities of Starch of Tacca 

 pinna tifida. 



