_Pea and Bean Starches._—These starches produce but a slight effect
with polarized light. The rings are scarcely visible, and the hilum is
stellate or much cracked along a median line, the bean more so than the
pea, the latter resembling fresh dough kneaded again into the center
as in making rolls, and the former the shape assumed by the same after
baking. The grains of both are somewhat variable in size, ranging from
0.025 to 0.10 millimeter in length, as shown in Figs. 52 and 53.
_Wheat Starch_ grains are quite variable in size, varying from 0.05
to 0.010 millimeter in diameter. They belong to the same class as
barley and rye, the hilum being invisible and the rings not prominent.
The granules are circular disks in form, and there are now and then
contorted depressions resembling those in pea starch. They are the
least regular of the three starches named and do not polarize actively.
The typical forms of these granules are shown in Fig. 54.
_Barley Starch_ is quite similar to that of wheat, but the grains do
not vary so much in size, averaging 0.05 millimeter. They have rings
which are much more distinct, and very small granules adhering to the
largest in bud-like forms, as seen in Fig. 55.
_Rye Starch_ is more variable in size, many of the granules not
exceeding 0.02 millimeter, while the largest reach 0.06 to 0.07
millimeter. It lacks distinctive characteristics entirely, and is the
most simple in form of all the starches. Fig. 56 shows the appearance
of the granules under the microscope.
_Oat Starch_ is unique, being composed of large compound masses of
polyhedral granules from 0.12 to 0.02 millimeter in length, the single
granules averaging 0.02 to 0.015 millimeter. It does not polarize
actively, and displays neither rings nor hilum. The illustration, Fig.
57, shows its nature with accuracy.
_Indian Corn Starch._—The granules of maize starch are largely of
the same size, from 0.02 to 0.03 millimeter in diameter, with now
and then a few which are much smaller. They are mostly circular in
shape or rather polyhedral, with rounded angles, as shown in Figs. 58
and 61. They form very brilliant objects with polarized light, but
with ordinary illumination show but the faintest sign of rings and a
well-developed hilum, at times star-shaped, and at others more like a
circular depression.
_Rice Starch_ is very similar to that of maize, and is easily confused
with it, the grains being about the same size. The grain, however,
is distinguished from it by its polygonal form, and its well defined
angles, as indicated in Fig. 59. The hilum is more prominent and more
often stellate or linear. Several granules are at times united.
_Cassava Starch._—This variety of starch is obtained from the root of
the sweet cassava, which grows in great profusion in Florida. It is
compared with maize starch in Figs. 60 and 61. In the illustration the
granules are represented as magnified 150 diameters. The grains of the
cassava starch measure about 0.012 millimeter in diameter and resemble
very nearly maize starch, except that they have greater evenness of
outline.[169]
For further descriptions of starch grains the reader is referred to the
work of Griffith, already cited.
These descriptions, it will be seen, do not agree entirely with those
of some other authors, but they are based on a somewhat extensive
experience.
There are peculiarities of size, shape and appearance of starch
granules, which must be allowed for, and the necessity for every
investigator to compare a starch which he is desirous of identifying
with authentic specimens, must always be recognized.