122 



or trlehites of soluble starch may be of a considerable size. Since the 

 crystals have nearly the same refractive index as the remainder of the 

 grain, they cannot be detected without special treatment. 



The structure of the starch grain is most easily seen in such grains as 

 those of the common potato, or of arrowr(H>t, which show the layers of 

 starch most plainly, or those of Hamlioo Brier root, which show the charac- 

 teristics of the central portion. When these starches are stained with 

 certain dyes, of which safranin is the best example, and the excess of stain 

 is extracted, the central portion retains the stain, and the crystalline na- 

 ture of this portion becomes evident. In the center of the grain crystals 

 are seen arranged with their longer axes extending radially from the 

 hiluni. The clefts in this crystalline mass mark the hilum. and the fis- 

 sures caused by the loss of moisture follow the longer axes of the crystals, 

 forming the fan-shaped markings often seen in the unstained grain. Fig. 1. 

 When the grains arc kept moist at 7A)° C. for some time, the moisture 

 passes through the outer layers, causing but little change in thiir structure, 

 but when the crystalline portion is reached, this swells up and slowly dis- 

 solves from its surface, becoming surroinided by a zone which stains deeply 

 witli iodiiie solutinn. indicating the pre.'-'ence of soluble st.in li. Tlie si'lution 

 and swelling of this inner portion pushes upward the outer layers, which 

 finally ruptnre at the thinnest ])oint. that is, at the hilum end in eccentric 

 grains. It therefore appears that the greater inoistni-e ointent of bis pdrtion 

 is due to its higher s(>]ul)iiity. and indeed tiiis i)art may be entirely dissolved 

 and carried away in solution before the outer layers are affected. This is 

 conunonly the case in such grains as those of the common yam. or of Ram- 

 lx)o Brier root. Fig. 4. 



Something of the chemical nature of the varioiis layers of the grain 

 can be determined by treatin.i: with the following easily i-ednciltie silver 

 solution, which may be compared to Febling's alk.-iline cnjiric tartrate 

 solution : 



Silver Nitrate 1 gm. 



Water 15 cc. 



Ammonia water q. s. 



Add the annnunia w.-iter to the solution of the silver niti'.ite until the 

 ]iretii)itate firsr formed .jnst dissolves. 



Potassium and Sodium Tartrate 2 gm. 



Water 15 cc. 



Dissolve. 



