e

d

198. (Fig. 190.) THEOBROMA. Cacao.
Paste, fine powder.

Cocoa, E. Kakao, G. Cacoa, Féves du Mexique, Fr.
The seeds of Theobroma cacao L., Sterculiaceæ.

Deep reddish brown; chocolate brown.

Mildly fragrantly aromatic.

Bitter and astringent.

Epidermal cells of seed small, polygonal, filled with deep brown coloring matter. A few multicellular deep brown trichomes. Thinwalled, collapsed parenchyma; selerenchyma layer. Endosperm cells thin-walled, polygonal, filled with fat and some compound starch. Hull remnants showing mechanical tissue of rather thick-walled, mostly elongated, porous cells. Spiral duct remnants and some crystals.

Cocoa and chocolate are variously adulterated with ground cocoa shells, starch, rice, flour, cocoa butter, lard, and other substances. Shells should not exceed 3.5 per cent. Shell adulteration may be determined quantitatively by the method described in Part I.

a

9

Fig. 190. THEOBROMA.

a. Epidermal cells of seed.

b. Endosperm cells with fat and starch, longitudinal view. c. Trichomes.

d. Mechanical cells of hull.

e. Endosperm cells.

f. Parenchyma.

g. Sclerenchyma, top view.

h. Sclerenchyma cells, profile view.

i. Spiral ducts which are abundant in the shell tissue. j. Mucilaginous substance characteristic of shell tissue.

199. (Fig. 191). TRAGACANTH. Gum Tragacanth. U. S. The dried gummy exudation of Astragalus gummifer Lab., Leguminosa. Snow white to light brownish.

Odorless.

Highly mucilaginous.

In water mounts the particles immediately swell and become translucent, showing lamellate lines and markings, with here and there groups of simple, nearly spherical starch granules, measuring from 4 to 8 in diameter. Tincture of iodine reveals yellowish striæ and groups of organic particles marking the interstices and lines of separation of the lamellate particles. The quality of tragacanth is inversely proportional to the amount of starch present. In the crude drug (not powdered) the quality is also indicated by the color, the lighter and more translucent the article (as in the ribbon or vermicelli variety) the purer and better it is. The brown article (sorts) will show abundant starch.

Ash should not exceed 3 per cent.

The powdered article is likely to be made from the inferior sorts and refuse. It may be adulterated with India gum, cherry gum and other spurious vegetable gums. Gum tragacanth is much employed for adulterating purposes; as ice cream and sausage meat fillers, as thickening agents, in egg substitutes, etc.

Fig. 191. GUM TRAGACANTH. A bit of the gum mounted in water and examined under a medium power. a, the gum presents a somewhat striated appearance, interrupted by organic matter which takes on a bright yellow coloration with tincture of iodine (c); b, groups of simple starch granules are distributed through the gum. The better the quality of tragacanth the fewer the starch granules, but even the highest grade contains some starch.