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are large oval or pyriform cells, often containing shrivelled cell contents. Common measurements of these cells are 008 inch small diameter, 0176 inch long diameter for the oval cells, and for the pyriform 0136 inch broad end, 0184 long diameter.

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Fig. 18.-a, Pulp cells of strawberry, x 115; b, strawberry seed, x 20.

The Raspberry has its seeds reticulated, and in most jams the form of the fruit is preserved quite sufficiently for recognition.

The Gooseberry has an epidermis in which can be seen a mosaic pavement of cells, and the fruit also possesses clavate hairs.

The Blackberry-the seeds are reticulated, and the cuticle covered with stellate hairs.

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The

Currants.-Both the black and the red currant are similar in structure : the epidermis is covered with an excessively thin membrane, showing sinuous wavy divisions, and set with simple hairs. Beneath the outer membrane are the colour layers, consisting of little square masses with rounded angles about 00029 to 00039 inch diameter (a, fig. 19). pulp is made up of thin-walled cells, and, lastly, here and there may be found peculiar compouud bodies, b, attached to the inner layer of the epidermis. These are about 0058 inch in length and 0015 inch in breadth, and are formed of a number of oblong cells. So far as known, these bodies are found only in the currant.

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Fig. 19.-a, A shred of epidermis, showing the sinuous markings in one portion, and the under layer of cells in another; b, the compound bodies, x 115.

STARCH, CH1005.

§ 80. It is convenient to consider the starches together, more especially as, however varied in form, the chemical composition of all starch is very similar, if not identical.

Every starch corpuscle is composed of at least two probably isomeric bodies, the one granulose," soluble in saliva, and

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coloured blue by iodine; the other coloured by iodine pale yellow, and only becoming blue after the addition of sulphuric acid; it is fully soluble in ammoniacal oxide of copper, and appears to agree very closely with the characters of cellulose.

These two substances may be most readily separated by diluted chromic acid, which dissolves granulose very easily, whilst cellulose remains unaltered. All starch is very hygroscopic wheat starch, dried in a vacuum, still contains 11 per cent. of water, and air-dried from 16 to 28 per cent. of water. Starch is insoluble in cold water or spirit. Some chemists, indeed, assert that if finely powdered in agate mortars, or with quartz sand, a small portion dissolves; others contend that this is no true solution, but the starchy matter in a state of most minute division. If warmed with water, the starch granules swell, and when heated up to 100° most starches form a semisolution in water. True compounds of starch with bases are scarcely established. Lime and baryta appear to form weak unions, and the intense colour produced by iodine, as well as bromine, seems to point to the formation of haloid combinations. Fritsche, indeed, states that he has isolated the iodide and the bromide of starch, the former containing ten equivalents of starch and one of iodine.

Starch heated in closed tubes up to 100°C. changes gradually into soluble starch. If the temperature is raised up to 160° or 200°C., it forms a transparent mass, consisting wholly of dextrine. At 220° to 280° still further change is produced, and the result is pyrodextrine, a substance easily soluble in water (but insoluble in absolute alcohol and ether), and with the composition of C18H36036HO. At still higher temperatures there is carbonisation, and the formation of products similar to those caused by the decomposition of sugar.

Starch is easily changed into sugar by the action of dilute mineral acids, as well as by oxalic acid, aqueous chloride of zinc, and by certain ferments-diastase, saliva, yeast, &c.

The estimation of starch in organic bodies generally is best carried out as follows:-The powdered and dried substance is heated in a 5 per cent. solution of caustic potash in absolute alcohol, in a closed tube, in the water-bath for twenty-four hours, and filtered while hot. The residue is washed first with absolute alcohol, and then with ordinary alcohol, dried, and heated with a solution of 2 per cent. hydrochloric acid, in a flask fitted to a vertical condenser, until a blue colour is no longer produced by iodine. (See also p. 113.) The sugar is then estimated in the ordinary way.

Microscopical Identification of Starches.

The successful microscopical examination of starches requires practical study, and those who desire to identify them must use all drawings and descriptions as guides merely. It is not easy to preserve starches mounted as microscopical objects, and the analyst is therefore recommended to fit up a little case, in small, wide specimen-tubes, so that he can have at hand a sample of every kind of starch possible to be obtained. These samples should be arranged in the five following classes, partly based on Dr. Muter's † classification.

A high magnifying power is not required, save for the very minute starches, such as rice and pepper. For ordinary work a magnifying power of 250 diameters is ample. Dr. Muter's classification of starches was founded on observations with a B micrometer eyepiece and a-inch power.

It is also useful to observe the various samples of starch, and make tables of their dimensions. The proper way to do this is to put the smallest possible quantity of the well-mixed starch on a glass slide, add a droplet of distilled water, cover with a thin glass, take the exact size of all the starches in the field, enumerate them, and work them out into percentages for future reference.

The illumination of starches is to be particularly attended to. The light must strike obliquely through the granules, in order to observe the rings, which are by no means so easily seen as diagrams would indicate.

Polarised light is also useful, especially in the diagnosis of certain starches. Thus, the polarised starch of wheat, when examined in water, exhibits a dull cross; that of jalap, in shape and size like wheat, polarises brightly. Polarised light, in conjunction with a selenite plate, will also be found of great service. Red and green selenites are best, and give a beautiful play of colours with the arrow-roots and potato starch; while the starches of wheat, barley, rice, and oats, scarcely show any colour. The whole of the starches of the Leguminosæ are, so far as they have been hitherto examined, likewise destitute of this power of brilliant colouration. A 4-inch object-glass, with an A eyepiece, will be found better adapted for this method of research than higher powers.

If adulteration in any case has been made out, approximative quantitative results may be obtained by making a standard

According to Muter, a mounting medium of 1 part of glycerine to 2 of water preserves the characters of starch longest.

+"Organic Materia Medica." London, 1878.

mixture of the genuine starch with the adulterant found, and then counting the individual grains in the microscopic field. Thus, for example, supposing oatmeal to be found adulterated with barley-starch, and from a preliminary examination the mixture is thought to be 40 per cent., we proceed as follows:

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Pure barley-meal and oatmeal are carefully dried at 100°C. and mixed so that the mixture is exactly 40 per cent. A few grains of this powder are now rubbed up with glycerine and alcohol into a smooth paste, which is then further diluted to a certain bulk, a drop taken out with a glass rod, and covered with a glass, which is gently pressed down. The number of grains of barley and oat starch are now counted, and their relative proportion noted, and an exactly similar process is applied to the oatmeal in question.* If proper care be taken to repeat the experiments, the result is a near approximation to the truth. If photographs are taken of these mixtures, they are always at hand for reference, and much time is saved.

DIVISION I.-STARCHES SHOWING A PLAY OF COLOURS WITH POLARISED LIGHT AND A SELENITE PLATE.

CLASS I.-The hilum and concentric rings clearly visible, all the starches oval or ovate. The group includes tous les mois, potato, arrow-root, calumba, orris-root, ginger, galangal, and turmeric.

Tous les mois, or Canna arrow-root, is furnished by the Canna edulis, nat. order Marantacea. The granules vary in diameter from 0469 to 132 mm. [0018 to 0052 inch]. They present themselves under several forms, the smaller being granular or ovoid, the larger pyriform, whilst the largest granules are flat, oval, and pointed at their extremities. The hilum is annular, eccentric; the rings are incomplete, extremely fine, narrow, and regular. The starch dissolves easily in boiling water; solution of potash causes the granules to swell rapidly, and gives to the hilum and lines remarkable clearness.

Tous les mois can only be confused with the potato; the size is the chief distinction. The granules burst in water at 72°., and they give a more regular cross when examined by polarised light than those of the potato.

Curcuma arrow-root, which is also called East Indian (though the arrow-root ordinarily sold as East Indian is a Maranta), is furnished by the Curcuma angustifolia. The granules are elon

* See a paper by E. L. Cleaver, F.C.S., Analyst, January 31, 1877.

gated triangular, or irregularly oval, flattened, and almost transparent. The normal measurement varies from 0304 to 0609 mm. [0012 to 00238 inch]. The hilum is eccentric, not very distinct; the concentric rings are clearly visible, and form segments of a circle. The application of heat or a solution of potash deforms the grains in a very irregular manner; they begin to swell about 72°.

Maranta arrow-root, syn. Jamaica, St. Vincent, is derived from Maranta arundinaceœ. The granules are somewhat ovoid flattened, and tending to a triangular shape in the larger, but the smaller may be circular. The concentric layers are always visible and numerous, but not very marked. Nucleus is central, or about eccentric-in some circular, in others linear; from the nucleus a little slit, filled with air, often goes to the edge. Length of granule 0010 to 0-070 mm., average 0.036 mm. [= 00138 inch]. Tumefaction in water begins at 76°. The specific gravity of the starch taken in petroleum or benzole is 1-504; if dried at 100°, 1·565.

Natal arrow-root is probably the produce of Maranta arundinacea, the same plant from which Maranta itself is derived, but growing in a different climate. The majority of the granules are broadly ovate, but some are occasionally circular. The dimensions are from 0327 to 0375 mm. [00129 to 00148 inch]. The eccentricity of the hilum ranges between 1 and . The laminæ appear under water with special clearness, and on this account granules of Natal arrow-root have been frequently mistaken for those of the potato.

Potato starch, syn. Potato arrow-root.-The starch derived from the potato (Solanum tuberosum). The granules vary greatly in shape and size, some being small and circular, others large, ovate, and oyster-shaped. The hilum is annular, and the concentric rings incomplete. In the larger granules the rings are numerous and distinct. The normal dimensions are 06 to 10 mm. [0024 to 0039 inch]. The eccentricity averages. The granules float on chloroform.

Potato starch is frequently used as an adulterant of the arrowroots. The most reliable method of examination is careful microscopic observation, but there is also a different behaviour with regard to reagents, viz. :—

(1.) Maranta arrow-root, mixed with twice its weight of hydrochloric acid, produces a white opaque paste, whereas potato starch treated similarly produces a paste transparent and jelly-like.

(2.) Potato starch evolves a disagreeable and peculiar odour when boiled with dilute sulphuric acid, which is not the case with arrow-root.

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