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DISTRIBUTION OF STARCH.

× Starch. This substance is, with the exception of protoplasm, the most abundant and universally distributed of all the cell-contents, occurring, as it does, more or less, in all parenchymatous cells (Fig. 10), except those of the epidermis. In its fully developed state it is, however, most abundant in the matured structures of plants, as the pith of stems, seeds, roots, and other internal and Subterranean organs which are removed from the influence of light.

FIG 10.-Cell of

the Potato con

taining starch

granules.

Starch is not only widely distributed through the different parts of a plant, but it also occurs in varying quantity in all classes of plants with the exception of the Fungi. West Indian Arrow-root (Fig. 11), Sago (Fig. 12), Tous

FIG. 11.-West-India Arrowroot (x 250). FIG. 12.-Sago meal (x 250). FIG. 13.Tous-les-mois (x 250). FIG. 14.-Potato starch (x 250).

les-mois (Fig. 13), and Potato starch (Fig. 14) may be mentioned as familiar examples of starches derived from different plants.

When fully formed, starch is found floating in the cellsap (Fig. 10) in the form of colorless granules or grains, which are either distinct from one another as is usually the case (Fig. 10), or more or less combined together so as to form compound granules.

In form the separate granules are always spherical or nearly so in their earliest condition. In some cases this form is nearly maintained in their mature state, as in

FORM AND SIZE OF STARCH GRAINS. II

Wheat starch (Fig. 15), but the granules frequently assume other forms, as ovate, elliptical, more or less irregular, club shaped, or angular (Figs. 10-16). Starch granules vary also extremely in size in different plants, and even in the same cell of any particular plant. The largest granules known appear to be those of Canna starch (Fig. 13), or, as it is com

FIG. 15.-Wheat starch (x 250).

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FIG. 16.-Rice starch
(x 250).

monly termed, "Tous-les-mois," where they are sometimes as much as the of an inch in length; while the smallest granules, among which may be mentioned those of Rice starch (Fig. 16), are frequently under of an inch in length.

Development of Starch.-Starch first makes its appearance as minute colorless granules in the interior of the chlorophyl grains when exposed to sunlight, as previously noticed at page 9. These primary starch granules, however, rarely grow to any considerable size, but are dissolved, chemically altered, and poured out into the sap, of which they then form a part. A portion of this primary starch may be used by the protoplasm of the cell in which it is formed for the manufacture of its cell-wall, but by far the greater part is handed down from one cell to another till it arrives at particular parts of the plant, when it becomes rcorganized and stored up for future use. In this latter state starch assumes its more characteristic appearance. Thus in a well-developed Potato granule (Fig. 14), we may observe a roundish dark spot, termed the nucleus or hilum, which is commonly situated near one end of the granule; and surrounding this a variable number of faint lines which alternate with other darker ones, so that the whole presents the appearance of a series of more or less irregular concentric shells placed around a common point,

12

DEVELOPMENT OF STARCH.

The starch granules of different plants vary very much in the character of their hilum, and in the distinctness and general appearance of their concentric lines, in the same way as they vary exceedingly in form and size when obtained from different sources; those, however, which are derived from the same plant are more or less uniform in appearance, so that a practiced observer may distinguish under the microscope the different kinds of starch, and refer them to the particular plants from whence they have been derived.

Sometimes there is more than one hilum in a starch granule, and, as growth then takes place round each, compound granules are formed. Starch is insoluble in cold water, alcohol, ether, and oils. By the action of boiling water it swells up and forms a mucilage or paste; and, if to this when cooled iodine be added, a deep blue color is produced. If starch be exposed to a temperature of about 320° F., for a short time, it is converted into a soluble gummy substance, called dextrin or British gum.

Raphides.-This name is now more generally applied to all inorganic crystals of whatever form which are found

FIG. 17.-Conglomerate raphides of the Beet. FIG. 18.-Acicular or true raphides of a species of Rumex. Two of the cells contain raphides, and three chlorophyl granules. FIG. 19.-Cystolith, from Parietaria officinalis. (After Henfrey.)

in the cells of plants, although the term raphides (which is the Greek for needles) was originally given to those only that were shaped like a needle (Fig. 18.) Raphides have

RAPHIDES-CRYSTALLOIDS.

13

been found more or less in nearly all orders of plants, and in all their organs; but they are most abundant in the stems of herbaceous plants, in the bark of woody plants, and in leaves and roots. These crystals are usually found in the cavities of the cells, but they also occur in their walls, as the cell walls of the Coniferæ and Gnetaceæ.

When found in the interior of cells, they either occur singly, as in the inner bark of the Locust tree, or far more commonly there are a number of crystals in the same cell. In the latter case they are usually either placed side by side, as in the stem of Rumex (Fig. 18); or in groups radiating from a common point, so as to assume a clustered or conglomerate appearance, as in the stem of the common Beet (Fig. 17). The former have been termed acicular or true raphides, and the latter conglomerate raphides or sphæraphides. A cystolith is a globular mass of crystals suspended from the cell wall, as seen in Fig. 19.

Crystalloids, Aleurone Grains, and Globoids.

Besides the inorganic crystals just described, it frequently happens that some of the protoplasmic matter in the cells

14

ALEURONE GRAINS.

--that is, in those cells in which reserve food material is stored up-assumes a crystalline form, and becomes cubical, octahedral, tetrahedral, rhomboid. These crystalline masses are known as crystalloids or proteine crystals (Fig. 20). Small roundish and colorless albuminous grains, which are termed proteid or aleurone grains, are found in the cells of ripe seeds. In these grains the crystalloids are frequently found imbedded, and also peculiar small round bodies, which are composed of double phosphate of calcium and magnesium, termed globoids (Fig. 20).

The aleurone grains and crystalloids are evidently reservoirs of protein, to be used when growth becomes active in the process of germination, in the same way that starch and oily matters are reservoirs of hydrocarbons for use in a like manner.

II. Forms and Sizes of Cells.-When growth is uniform, or nearly so, on all parts of the cell-wall, we have spherical or rounded cells (Fig. 22). When it is greater at

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FIG. 22.

FIG. 23.

FIG. 24.

FIG. 25.

FIG. 22.-Rounded cells. FIG. 23.-Oblong or oval cell. FIG. 24.-Polygonal cells in combination; these cells are pitted. FIG. 25.-Stellate cells.

the two extremities than at the sides, the form is oval or oblong (Fig. 23). But, under other circumstances, in consequence of the mutual pressure of surrounding cells, they become polygonal in form (Fig. 24).

Secondly, when the growth is nearly uniform on all sides of the cell-wall, but not equally so at all points of its surface, we have cells which maintain a rounded form in the center, but with rays projecting from them in various directions, by which they acquire a more or less star-like