NON-PROTOPLASMIC CELL CONTENTS 77 
STRUCTURE AND Composition oF StTarcu.—Starch grains 
vary in shape from spheroidal to oval to conchoidal to polygonal. 
They are composed of layers of soluble carbohydrate material 
and probably other substances called ‘“‘/amella,” separated from 
each other by a colloidal substance resembling a mucilage in its 
behavior toward aniline dyes. They contain a more or less 
distinct highly refractile point of origin or growth called the 
“‘fulum,” which also takes the stain of an aniline dye. The layers 
of carbohydrate material stain variously, blue, indigo, purple, 
etc., with different strengths of iodine solutions. Each grain is 
covered with a stainable elastic membrane. 
Starch grains may be grouped, according to the condition in 
which they are found in the cells of storage regions into three kinds, 
viz.: simple starch grains, compound starch grains and fill starch grains. 
Simple starch grains are such as occur singly. Compound 
starch grains occur in groups of two, three, four, five, six or 
‘ more and are designated as two-, three-, four-, five-, six-, etc., 
compound, according to the number of grains making up the 
group. Fill starch grains are small grains filling up the spaces 
between the larger grains in storage cells. ‘These are common in 
commercial starches. 
MetTHopD oF EXAMINING RESERVE STARCHES.—Many of the 
reserve starches are used commercially, such as potato, corn, rice, 
maranta, oat, wheat, sago, tapioca, etc., and it frequently 
becomes necessary for the microscopist to determine their purity 
or their presence in a sample of food or drug. The following 
characteristics should be noted in determining the identity or 
source of the starch. 
1. The shape of the grain. 
2. Whether simple or compound or both; if compound, the 
number or range in numbers of grains composing it. 
3. The size of the grain in microns. 
4. The position of the hilum, if distinct; whether central or 
excentric (outside of the center). 
5. The shape of the hilum and the degree to which it is often 
fissured. 
6. The nature of the lamellz, whether distinct or indistinct; 
if distinct, whether concentric (surrounding the hilum) or eccen- 
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