Potato starch grains are very variable in size, being found from .05 to .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. 4, but the frequency of the smaller granules is not as evident as in Figs. 5 and 6. The layers in some granules are very plain and in others are hardly visible. They are rather more prominent in the starch obtained from a freshly cut surface. The rings are more distinct 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 granules. The hilum appears as a shadowy depression (Fig. 4) and, with polarized light, its position is well marked by the junction of the arms of the cross. It will be found by comparison of Fig. 6 and Fig. 7, that in the potato it is more often at the smaller end of the granules, and that in the arrowroot it is at the larger. With polarized light and a selenite plate a beautiful play of colors is obtained. The smaller granules, by their nearly round shape, may be confused with other starches, but their presence at once serves to distinguish them from Maranta or Bermuda arrowroot starch. Rarely, compound granules are found composed of two or three single ones each within its own nucleus. Of the same type as the potato starch are various arrowroots. The only ones commonly met with in this country are the Bermuda, the starch of the rhizome of Maranta arundinacea, and the starch of tumeric. MARANTA STARCH The granules are not usually so varied in size or shape as those of the potato, as may be seen in Figs. 8, 9, and 10. They average about .07 millimeters in length. They are about the same size as the average of those of the potato, but are never found as large or as small. This fact, 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 starches without difficulty. With polarized light, the results are similar to those seen with potato starch, and, by this means, the two varieties may be readily distinguished by displaying, in a striking way, the forms of the granule and the position of the hilum, as is illustrated in Figs. 8 and 9. CIRCUMA Circuma, or tumeric starch (Fig. 11), though of the arrowroot class, is quite distinct in appearance from these we have described, being most irregular in outline, so that it is impossible to define its shape or to do more than to refer to the illustration. Many of the granules are long and narrow and drawn out to quite a point. The rings are distinct in the larger, and the size is about that of Maranta.