In studying starches use cold water as the mounting medium, because in cold water the form and structure are best shown, and because there is no chemical action on the starch. On the other hand, the form and structure will vary considerably if the starch is mounted in hot water or in solutions of alkalies or acids. The hilum appears colorless when in sharp focus, and black when out of focus.
Starch grains, when boiled with water, swell up and finally disintegrate to form starch paste.
Starch paste turns blue upon the addition of a few drops of weak Lugol solution. Upon heating, this blue solution is decolorized, but the color reappears upon cooling. If a strong solution of Lugol is used in testing, the color will be bluish black.
PLATE 72
Starch
1. Orris root (Iris florentinia L.).
2. Stillingia root (Stillingia sylvatica, L.).
3. Calumba root (Jateorhiza palmata, [Lam.] Miers.).
PLATE 73
Starch
1. Male fern (Dryopteris marginalis, [L.] A. Gray).
2. African ginger (Zingiber officinalis, Rosc.).
3. Yellow dock (Rumex crispus, L.).
4. Pleurisy root (Asclepias tuberosa, L.).
