Iodine solution—water 15 parts, iodide of potash 20 parts, iodine 5 parts; water distilled.
Balsam in benzol and glycerine jelly are desirable for mounting media, and some wax sheets will be needed for making cells. In addition, the analyst should supply himself with specimens of whole spices, starches, and known adulterants, which may be used to become acquainted with the forms and appearances to be expected; it is easier to begin one’s study in this way on sections prepared with the knife, and afterwards the powdered substance may be taken up.
To study the physiological structure in the spices and their adulterants is quite difficult, as the vegetable tissues which make up the structure of the spices and the materials of a vegetable origin which are added as adulterations consist of cells of different forms and thickness; those which are most prominent and common are the parenchyma, the sclerenchyma fibrous tissue, and the fibro-vascular bundles. Spiral and dotted vessels are also common in several of the adulterants, and in the epidermis are other forms of tissue which it is necessary to be well acquainted with, though not physiologically. The parenchyma is the most abundant tissue in all material of vegetable origin, making up the largest proportion of the main part of the plant. It is composed of thin wall cells which may be recognized in the potato and in the interior of the stems of maize. In the latter plant, also, the fibro-vascular system is well exemplified, running as scattered bundles between the nodes or joints. Fibrous tissue consists of elongated thick-walled cells of fibers which are very common in the vegetable kingdom and are well illustrated in flax, but they are not so commonly used for adulterating purposes. They are optically active, and in the shorter forms they somewhat resemble the cells next described. They are seen in one of the coats of buckwheat hulls and in the outer husks of the cocoanut.
The sclerenchyma is found in the shells of many nuts and in one or two of the spices, the cells being known as stone cells, from the great thickening of their walls. To them is due the hardness of the shell of the cocoanut, the pits of the olive, etc. (See [Fig. 1.]) Spiral and dotted vessels are common in woody tissue and are readily recognized. All these forms an analyst should make himself familiar with.
In pepper and mustard the parenchyma cells are prominent in the interior of the berry, while those constituting the outer coats are indistinct in the pepper, because of their deep color; but in the mustard are characteristics of this particular species. In fact, in many of the spices, and especially those which are seeds, the forms of the epidermal cells are very striking, and, if no attempt is made to classify them their peculiarities must be carefully noted, as the recognition of the presence of foreign husky matter depends upon a knowledge of the normal appearance in any spice.
The fibro-vascular bundles are most prominent in ginger and in the barks, while in the powdered spices they are found as stringy particles. The sclerenchyma, or stone cells, as shown in [Fig. 1], are common in the adulterant, especially in cocoanut shells, where may also be seen numerous spiral cells, and in the exterior coats of fibrous tissue. As to aids to distinguish these structures, the following peculiarities may be cited:
Fig. 1. STONE CELLS
Fig. 2. STARCH STAINED WITH IODINE
Fig. 3. Starch, plain
Fig. 4. POTATO STARCH
Fig. 5. Potato
The stone cells and fibrous tissue are optically active, and are, therefore, readily detected with polarized light, shining out in the dark field of the microscope as silver-white or yellowish bodies.
The fibro-vascular bundles are stained deep orange brown with iodine, owing to the nitrogenous matter which they contain, while parenchyma is not affected by this reagent, aside from the cell contents, nor has it any action on polarized light, remaining quite invisible in the field with crossed prisms.