Part 36

=202. Description Of Typical Starches.=—The more commonly occurring starches are described by Richardson as they appear under the microscope magnified about 350 diameters.

The illustrations, with the exception of the cassava starch, and the maize starch accompanying it were drawn by the late Dr. Geo. Marx from photographs made by Richardson in this laboratory. The two samples excepted were photographed for the author by Dr. G. L. Spencer.

Maranta Starch.—Of the same type as the potato starch are the various arrowroots, the only one of which commonly met with in this country being the Bermuda, the starch of the rhizome of Maranta arundinacea, and the starch of turmeric.

The granules are usually not so varied in size or shape as those of the potato, averaging about 0.07 millimeter in length as may be seen in Fig. 48. They are about the same size as the average of the potato, but are not often found with the same maximum or minimum magnitude, which circumstance, together with the fact that the end at which the nucleus appears is broader in the maranta and more pointed in the potato, enables one to distinguish the two starches without difficulty. With polarized light the results are similar to those seen with potato starch, and this is a ready means of distinguishing the two varieties, by displaying in a striking way the form of the granule and position of the hilum.

Potato Starch.—The starch grains of the potato are very variable in size, being found from 0.05 to 0.10 millimeter in length, and in shape from oval and allied forms to irregular and even round in the smallest. These variations are illustrated in Fig. 49, but the frequency of the smaller granules is not as evident as in some other cases. The layers are visible in some granules with great distinctness and in others hardly at all, being rather more prominent in the starch as obtained from a freshly cut surface. The rings are more distinct, too, near the hilum or nucleus, which in this, as in all tuberous starches, is eccentric, shading off toward the broader or more expanded portion of the granule. The hilum appears as a shadowy depression, and with polarized light its position is well marked by the junction of the arms of the cross. With polarized light and a selenite plate a beautiful play of colors is obtained. The smaller granules, which are nearly round, may readily be confused with other starches, but their presence serves at once to distinguish this from maranta or Bermuda arrowroot starch. Rarely compound granules are found composed of two or three single ones each with its own nucleus.

Ginger Starch.—This starch is of the same class as those from the potato and maranta and several others which are of underground origin. In outline the granules are not oval like those named, but more rectangular, having more obtuse angles in the larger ones and being cylindrical or circular in outline in the smaller, as indicated in Fig. 50. They average nearly the same size as maranta starch, but are much more variable, both in size and form. The rings are scarcely visible even with the most favorable illuminations.

Sago Starch.—This exists in two modifications in the market; as raw and as prepared sago. In the prepared condition it is characterized by a larger circular depression in the center of most of the granules. The rings are not visible. They are mostly circular in form or approaching it, and vary from 0.025 to 0.065 millimeter in diameter, as indicated in Fig. 51.

DRAWN BY GEO. MARX.

A. Hoen & Co., Lithocaustic]

DRAWN BY Geo. MARX.

A. Hoen & Co., Lithocaustic]

PLAIN ILLUMINATION.]

PLAIN ILLUMINATION.

A. Hoen & Co., Lithocaustic]

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.

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.

AUTHORITIES CITED IN PART SECOND.

Vines, Vegetable Physiology.

Berichte der deutschen chemischen Gesellschaft, Band 23, S. 2136; Stone, Agricultural Science Vol. 6, p. 180. Page 59, eighth line from bottom insert “original” before “optical.” Page 60, second line from top, read d instead of l fructose.