MORPHOLOGY OF HIGHER PLANTS. 165 



(9) Behavior toward various reagents, as chromic acid, cal- 

 cium nitrate, chlor-zinc-iodide, diastase and various anihne stains, 

 showing pecuharities of both structure and composition (Fig. 96). 



General Properties of Starch. If starch is triturated with 

 water and the mixture filtered, the filtrate does not give a reaction 

 with iodine solution ; if, on the other hand, the starch is previously 

 triturated with sand and then with water, the filtrate becomes blue 

 on the addition of iodine solution. It appears that in the latter 

 operation the wall of the grain is broken and the soluble starch 

 present in the grain is liberated. 



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 wath iodine. If, how- 

 ever, a mineral acid be added, it is ciuickly 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 efifect 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 efifects 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. 



Inulin appears to be an isomer of starch and occurs in solu- 

 tion in the ceH-sap of various members of the Compositae and 



