Aggregate starch (Plate 76) varies greatly in size, form, and in the nature of the starch grains forming the aggregations.
Compound starch grains may be composed of two or more parts, and they are designated as 2, 3, 4, 5, etc., compound (Plate 75).
The parts of a compound grain may be of equal size (Plate 75, Fig. 4), or they may be of unequal size (Plate 75, Fig. 2).
In most powders large numbers of the parts of the compound grains become separated. The part in contact with other grains shows plane surfaces, while the external part of the grain has a curved surface. There will be one plane and one curved surface if the grain is a half of a two-compound grain; two plane and one curved surface if the grain is a part of a three-compound grain, etc.
The simple starch grains forming the aggregations become separated during the milling process and occur singly, so that in the drugs cited above the starch grains are solitary and aggregate.
Many plants contain both simple and compound starch grains (Plate 74, Fig. 3).
In some forms—e.g., belladonna root (Plate 75, Fig. 2) the compound grains are more numerous; while in sanguinaria the simple grains are more numerous, etc.
OUTLINE
The outline of starch grains is made up of (1) rounded, (2) angled, and (3) rounded and angled surfaces.
Starch grains with rounded surfaces may be either spherical, as in Plate 74, Fig. 3, or oblong or elongated, as in Plate 71, Fig. 1.