CELL-CONTENTS AND FORMS OF CELLS. 147 



If dry starch and iodine are triturated together no color or, 

 at the most, a faint blue color is produced ; whereas, if a little 

 water is added and the trituration repeated, a deep blue color is 

 immediately produced. 



The blue color of starch solution and iodine disappears on the 

 application of heat, but slowly returns on cooling the solution, 

 but not with the same degree of intensity, part of the iodine 

 being volatilized. 



When starch is heated with glycerin it dissolves, and if alco- 

 hol is added to the solution, a granular precipitate is formed which 

 is soluble in water, the solution giving a blue reaction with iodine. 



When starch is heated with an excess of water at 100 C. for 

 even several weeks, dextrinization of the starch does not take 

 place ; i.e., the solution still gives a blue color with iodine. If, how- 

 ever, a mineral acid be added, it is quickly dextrinized, turning 

 violet-red, reddish, and yellowish with iodine ; finally, maltose 

 and dextrose are produced, these giving no reaction with iodine, 

 but reducing Fehling's solution. The ferments and other chemi- 

 cals have a similar effect on starch. 



When dry starch is heated at about 50 C. from 15 to 30 min- 

 utes the lamellae and crystalloidal structure become better defined 

 and the polarizing effects produced by the grains also become 

 more pronounced. When starch is mounted in a fixed oil, as 

 almond, the polarizing effects are more pronounced than when 

 it is mounted in water, but the inner structure is not usually 

 apparent, unless the starch has been previously heated. (For 

 literature on the starch grain see Kraemer, Bot. Gazette, Vol. 

 XXXIV, Nov., 1902 ; Ibid., Vol. XL, Oct., 1905 ; also Eighth In- 

 ternational Congress of Applied Chemistry, Vol. 17, p. 31.) 



BOTANICAL DISTRIBUTION OF STARCH. This constituent is 

 commonly present as a reserve material in a large number of 

 plants. The sources of the commercial starches are constantly 

 being extended. The commercial starches are chiefly obtained 

 from one or more genera of the Gramineae, Marantaceae, Eu- 

 phorbiaceae, and Solanaceae. The following is a list of the fami- 

 lies yielding one or more economic products which contain 

 starch : Cycadaceae, Gramineae, Araceae, Liliaceae, Amaryllida- 

 ceae, Iridaceae, Musaceae, Zingiberaceae, Cannaceae, Marantaceae, 



