Form Of Aleurone Grains

Much attention has been given to the study of the special parts of the aleurone grains, but one of the most important diagnostic characters has been overlooked, namely, that of comparative form. For the purposes of comparing the forms of different grains, they should be mounted in a medium in which the grain and its various parts are insoluble. Oil of cedar is such a medium. The variation in form and size of the aleurone grains when mounted in oil of cedar is shown in Plate 77a.

Description Of Aleurone Grains

The aleurone grains of curcas (Plate 77a, Fig. 1) vary in form from circular to lens-shaped, and each grain contains one or more globoids. The globoids are larger when they occur singly. In sunflower seed (Plate 77a, Fig. 2) the grains vary from reni-form to oval, and one or more globoids are present; many occur in the center of the grain.

The aleurone grains of flaxseed (Plate 77a, Fig. 3) resemble in form those of sunflower seed, but the grains are uniformly larger and some of the grains contain as many as five globoids.

In bitter almond (Plate 77a, Fig. 4) the aleurone grains are mostly circular, but a few are nearly lens-shaped. A few of the large, rounded grains contain as many as nine globoids; in such cases one of the globoids is likely to be larger than the others. The aleurone grains of croton-oil seed (Plate 77a, Fig. 5) are circular in outline, variable in form, and each grain contains from one to seven globoids.

In sesame seed (Plate 77a, Fig. 6) the typical grain is angled in outline and the large globoid occurs in the narrow or constricted end.

The aleurone grains of castor-oil seed (Plate 77a, Fig. 7) resemble those of sesame seed, but they are much larger, and many of the grains contain three large globoids. When these grains are mounted in sodium-phosphate solution, the crystalloid becomes visible.

Tests For Aleurone Grains

Aleurone grains are colored yellow with nitric acid and red with Millon's reagent.

The proteid substance of the mass of the grain, of the globoid, and of the crystalloid, reacts differently with different reagents and dyes.

The ground substance and the crystalloids are soluble in dilute alkali, while the globoids are insoluble in dilute alkali.

The ground substance and crystalloids are soluble in sodium phosphate, while the globoids are insoluble in sodium phosphate.

Calcium oxalate is insoluble in alkali and acetic acid, but it dissolves in hydrochloric acid.

Aleurone Grains.

Plate 77a. Aleurone Grains.

1. Curcas {Jatropha curcas, L.).

2. Sunflower seed {Helianthus annuus, L.).

3. Flaxseed (Linum usitatissimum, L.).

4. Bitter almond (Prunus amygdalus, amara, D.C.)

5. Croton-oil seed (Croton tiglium, L.).

6. Sesame seed (Sesamum indicum, L.).

7 and 8. Castor-oil seed (Ricinus communis, L.).

Crystals

Calcium oxalate crystals form one of the most important inorganic cell contents found in plants, because of the permanency of the crystals, and because the forms common to a given species are invariable. By means of calcium oxalate crystals it is possible to distinguish between different species. In butternut root bark, for instance, only rosette crystals are found, while in black walnut root bark - a common substitute for butternut bark - both prisms and rosettes occur. This is only one of the many examples which could be cited.

These crystals, for purposes of study, will be grouped into four principal classes, depending upon form and not upon crystal system. These classes are micro-crystals, raphides, rosettes, and solitary crystals.

Micro-Crystals

Micro-crystals are the smallest of all the crystals. Under the high power of the microscope they appear as a V, a Y, an X, and as a T. They are, therefore, three- or four-angled (Plate 78). The thicker portions of these crystals are the parts usually seen, but when a close observation of the crystals is made the thin portions of the crystal connecting the thicker parts may also be observed. Micro-crystals should be studied with the diaphragm of the microscope nearly closed and with the high-power objective in position. While observing the micro-crystals, raise and lower the objective by the fine adjustment in order to bring out the structure of the crystal more clearly. Micro-crystals occur in parenchyma cells of belladonna, scopola, stramonium, and bittersweet leaves; in belladonna, in horse-nettle root, in scopola rhizome, in bittersweet stems, and in yellow and red cinchona bark, etc.

The crystals in each of the above parts of the plant are similar in form, the only observed variation being that of size. Their presence or absence should always be noted when studying powders.

Micro Crystals.

Plate 78. Micro-Crystals.

1. Horse-nettle root (Solatium carolinense, L.).

2. Scopola rhizome (Scopola carniolica, Jacq.).

3. Belladonna root (Atropa belladonna, L.).

4. Bittersweet stem (Solanum dulcamara, L.).

5. Scopola leaf (Scopola carniolica, Jacq.).

6. Tobacco leaf (Nicotiana tabacum, L.).

7. Belladonna leaf (Atropa belladonna, L.).