18 FOUITOATIONS OF BOTANY 



nary commercial starch as used in the laundry, and as 

 sold for food in packages of cornstarch. When pure it 

 is characterized not only by its lustre, but also by its 

 peculiar velvety feeling when rubbed between the fingers. 



22. The Starch Test. — It is not always easy to recog- 

 nize at sight the presence of starch as it. occurs in seeds, 

 but it may be detected by a very simple chemical test, 

 namely, the addition of a solution of iodine.^ 



1 

 EXPERIMENT VIII " 



Examination of Familiar Seeds with Iodine. — Cut in two with a 

 sharp knife the seeds to be experimented on, then pour on each, drop 

 by drop, some of the iodine solution. Only a little is necessary; 

 sometimes the first drop is enough. 



If starch is present, a blue color (sometimes almost black) will 

 appear. If no color is obtained in this way, boil the pulverized 

 seeds for a moment in a few drops of water, and try again. 



Test in this manner corn, wheat (in the shape of flour), oats (in 

 oatmeal), barley, rice, buckwheat, flax, rye, sunflower, four-o'clock, 

 morning-glory, mustard seed, beans, peanuts. Brazil-nuts, hazelnuts, 

 and any other seeds that you can get. Report your results in tabu- 

 lar form as follows : 



Mttch Starch Little Starch No Starch 



Color : blackigh or Color : pale blue or Color : brown, orange, 

 dark blue. greenish. or yellowish. 



23. Microscopical Examination of Starch.* — Examine starch in 

 water with a rather high power of the microscope (not less than 200 

 diameters). 



1 The tincture of iodine sold at the drug-stores will do, but the solution 

 prepared as directed in the Handbook answers better. This may be made up 

 in quantity, and issued to the pupils in drachm vials, to be taken home and 

 used there, if the experimenting must be done outside of the laboratory or the 

 schoolroom. 2 May be a home experiment. 



8 At this point the teacher should give a brief illustrated talk on the con- 

 struction and theory of the compound microscope. 



