122 



iir ti'ii-liites ni" sdlubli' st.ii'fli may lie nl' n (•(nisideinlilc size. Siiic(> the 

 crystals have nearly the same relraetive index as the i i'iiiaiii(h-i- n( tlie 

 grain, tliey cannot 1)e detected \\ith(}nt sjiec-ial treat iiient. 



The structiii'e i>i the stanli pi-ain is must easily seen in such i;rains as 

 those of the common iiotato, or of arrowroot, whicli sliow the layers of 

 starcli nio8t jilainly. or those of I'amhoo I'l'ier root, whicli show the charac- 

 teristics of the centi'.al imrtinn. When these starches are stained with 

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

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

 ture of this ])ortiiin becomes evident. In the center of the grain ciystals 

 are si'en arranged witli their longer axes extending radially from tin- 

 hilnm. The clefts in this crystalline mass m;irk the hilum, and the fis- 

 sures caused hy the loss of moisture follow the longer axes of the crystals. 

 I'ormini,' the fan-slia]ied markings (il'ten seen in the unstained giain. Fig. 1. 

 When the grains are kv])t moist at ~>u° (". for s;inie time, the nmisture 

 passes through the outer layers, causing hut little chanv'e in their structure, 

 hut when the crystalline jiortion is r<'a<hed. this swells up and slowly dis- 

 s(>l\'es from its surface, becoming surinunded by a zone which stains d(>eiily 

 with iodii e sdlntiun, indicating the ]iiesence dl' s;ilnble starch. The solution 

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

 linally rupture at the thinnest jioint. tli.at is. at the hilum end in e(ceutric 

 grains. It therefore appears that the greater moisture content of his portion 

 is due to its higher solubilit.x'. and indeed this jiart may be entirely dissolved 

 and caii'ied away in solution l)efo)'e the outer layers are aU'ected. This is 

 connnonly thi' case in such grains as thos{> of the conunon \am, or nl' U.ini- 

 boo llriei- root. Fig. 4. 



Something of the chemical nature of th(> various layers of the 'iraiu 

 can he determined hy trer.ting with the following easily reducible silver 

 solution, which may Ik* compared to Fehling's alkaline cn|iric tartrate 

 solution : 



Sihcr Xili'atc' 1 gm. 



Watei' 15 cc. 



.\iinnonia. water (|. s. 

 .\i\t\ the .•iiiininnia water to Ibe sohition o! the siU'ci' nitrate until ibc 

 pi'ccipitalc fu'si liDancd Just dissolves. 



I'ot.assiiun and Sodium Tarlr.-ite D gm. 



Water 15 cc. 



Dissolve. 



