Other starches with rounded surfaces are shown on Plates 72 and 73.
Angled outlined grains are common to cardamon seed, white pepper, cubebs, grains of paradise (Plate 76, Fig. 4), and to corn (Plate 70, Fig. 3).
The outlines of all compound grains are made up partly of plane and partly of curved surfaces.
SIZE
The size (greatest diameter) of starch varies greatly even in the same species, but for each plant there is a normal variation.
In spherical starch grains the size of the individual grains is invariable, but in elongated starch grains and in parts of compound grains the size will vary according to the part of the grain measured. In zedoary starch (Plate 71, Fig. 4), for instance, the size will vary according to whether the end, side, or surface of the starch grain is in focus.
The parts of compound grains often vary greatly in size. Such a variation is shown in Plate 75, Fig. 2.
HILUM
The hilum is the starting-point of the starch grain or the first part of the grain laid down by the amyloplast. The hilum will be central if formed in the middle of the amyloplast, and excentral if formed near the surface of the amyloplast. It has been shown that the developing starch grain with eccentric hilum usually extends the wall of the amyloplast if it does not actually break through the wall. Starch grains with excentral hilums are therefore longer than broad.
