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Related article: 2. Starch. Starch is a carbohydrate having the chemical formula
of (CeHijOs^ which is generally found as the first visible product
of photosynthesis in most green plants. It is found in the chloro-
plasts and chroma tophores of green parts in the form of minute
granules. This kind of starch is known as Assimilation Starch.
Assimilation starch is dissolved during darkness within the chloro-
plasts by the action of ferments and passes into solution as a glucose
which is conveyed downward to those parts of the plant requiring
food. In its descent some of it is stored up in medullary ray cells,
and in various parts of the xylem, phloem, pith and cortex in the
form of small grains. Considerable, however, is carried down to
the underground parts, such as rhizomes, tubers, corms, bulbs
or roots, where the leucoplasts store it in the form of larger-sized
grains called Reserve Starch. This type of starch is generally
characteristic Avapro 300 for the plant in which it Avapro 300 is found. It constitutes
stored-up food for the plant during that period of the year when the
vegetative processes are more or less dormant.
Structure and Composition of Starch. Starch grains vary in
shape from spheroidal to oval to chonchoidal to polygonal. They
FIG. 35. Cell of Pellionia Daveauana, showing starch-grains. The black,
crescent-shaped body on the end of each grain is the leucoplast. Greatly enlarged.
are composed of layers of soluble carbohydrate material and prob-
ably other substances called " lamella," separated from each other by
a colloidal substance resembling a mucilage in its behavior Avapro 300 toward
aniline dyes. They contain a more or less distinct highly refractile
point of origin or growth called the " hilum" 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
Starch grains may be grouped, according to the condition in
which they are foiihd in the cells of storage regions into three
kinds, viz.: simple starch grains, compound starch grains and fill
Simple Avapro 300 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, Avapro 300 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.
Method 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 necesssary
for the microscopist Avapro 300 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 excen-
tric (outside of the center).
5. The shape of the hilum and the degree to which it is often
6. The nature of the lamellae, whether distinct or indistinct; if
distinct whether concentric (surrounding the hilum) or eccentric
(apparently ending in the margin and not surrounding the hilum),
or both, as in potato starch.
7. The color of the grains when stained with dilute iodine solu-
tions; whether indigo, blue, purple, red or yellowish-red, etc.
8. The appearance under polarized light.
9. The temperature at which the paste is formed.
10. The consistency of the paste.
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