. The microscopy of the more commonly occurring starches . entric in position, and show-ing no tendency to subdivision or extension. 7. There are no characteristic markings onthe surface of the grain of barley starch. Con-centric lines in the grain can only very rarelybe made out, although the darkening as theperiphery is approached often gives an appear-ance as if the grain were built up of concentriclayers. 8. On polarized light the grains act similarlyto those of rye (), but it is to be noticed thathere the black cross is always very indistinct. From the print it will be observed that i
. The microscopy of the more commonly occurring starches . entric in position, and show-ing no tendency to subdivision or extension. 7. There are no characteristic markings onthe surface of the grain of barley starch. Con-centric lines in the grain can only very rarelybe made out, although the darkening as theperiphery is approached often gives an appear-ance as if the grain were built up of concentriclayers. 8. On polarized light the grains act similarlyto those of rye (), but it is to be noticed thathere the black cross is always very indistinct. From the print it will be observed that inbarley starch there is a tendency for small areasof amorphous debris to appear in the field;this is so constant as to be of some value inidentifying the starch. Barley and Rye. Fig. 19 is from a negative taken by darkground illumination, and exposed twice, first toa field of barley starch and afterwards to oneof rye starch. Several very interesting facts arerevealed by this print. It will be observed thatthe definition of the barley starch is not at all. Fig. 19.—Barley and Rye Starches,(Dark Ground.) xll6. BARLEY STARCH 81 impaired by the second exposure, and the char-acters of both grains come out quite clearly, aseven where the grains are superposed in theprint the translucency of all the grains allowsboth outline and hilum to appear whereverpresent. There are several characteristic grainsof rye starch (recognised by the rayed hilum)present, while the general appearance of the field is indubitably that of barley starch. Thelarge circular grains without hilum or markingscannot be identified; they might be either wheator rye starch. CHAPTER XIV ARROWROOT STARCHES The arrowroot starches form a group by them-selves, in which the characters vary withincertain limits, rendering it impossible to giveone description which will be applicable to allin every detail. For the purpose of this investi-gation I have selected two : one, Bermuda arrow-root, representing the commoner forms;
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