PLATE 70
Starch
1. Calabar bean (Physostigma venenosum, Balfour).
2. Marshmallow root (Althæa officinalis, L.).
3. Field corn (Zea mays, L.).
PLATE 71
Starch
1. Galanga root (Alpinia officinarum, Hance). 2. Kola nut (Cola vera, [K.] Schum.). 3. Geranium rhizome (Geranium maculatum L.). 4. Zedoary root (Curcuma zedoaria, Rosc.). 4-A. Surface view of starch grain. 4-B. Side view of starch grain. 4-C. End view of starch grain.
In central hilum starch grains the grain is laid down around the hilum in the form of concentric layers. These layers are of variable density. The dense layers are formed when plenty of sugar is available, and the less dense layers are formed when little sugar is available. The unequal density of the different layers gives the striated appearance characteristic of so many starch grains.
In eccentric hilum starch grains the starch will be deposited in layers which are outside of and successively farther from the hilum.
The term hilum has come to have a broader meaning than formerly. Hilum includes at the present time not only the starting-point of the starch grain, but the fissures which form in the grain upon drying. In all cases these fissures originate in the starting-point, hilum, and in some cases extend for some distance from it. The hilum, when excentral, may occur in the broad end of the grain, galanga, and geranium (Plate 71, Figs, 1 and 3), or in the narrow end of the grain, zedoary (Plate 71, Fig. 4).
NATURE OF THE HILUM
The hilum, whether central or excentral, may be rounded (Plate 75, Fig. 1); or simple cleft, which may be straight (Plate 71, Fig. 1); or curved cleft (Plate 71, Fig. 2); or the hilum may be a multiple cleft (Plate 74, Fig. 3).