6 STUDY OF COMMON PLANTS. 



point of a knife. Mount in water a very small portion 

 of the powder thus obtained, and examine under a com- 

 pound microscope, first with the low, and afterward with 

 the high power. 



1. Numerous minute bodies are seen in the field of 



the microscope. These are grains of bean starch.^ 

 Are they all of the same size ? Of the same 

 shape ? Draw two or three of them. 



2. Focus carefully and study their structure. Are they 



homogeneous ? Compare different specimens in 

 regard to this point. 



3. Run a small drop of iodine solution under the cover 



glass and observe the effect. Notice from the 

 outside how far the reagent has advanced, then 

 examine that part of the slide under the micro- 

 ^ scope, and see how differently the starch granules 

 look after the iodine has acted upon them. 



II. Mount in the same way a bit of wheat flour taken 

 from the inside of a grain of wheat. 



1. How do the starch grains compare with those of the 



bean in form, size, and structure ? Are the grains 

 of wheat starch of uniform size ? 



2. Touch the cover glass lightly with a needle until 



some of the largest grains roll over. What is their 

 shape? Draw a few grains in different positions 

 so as to represent what you find to be charac- 

 teristic. 



3. Test with iodine solution. 



III. Examine corn starch obtained in the same way 

 from a grain of Indian corn. 



1 Useful suggestions for the miorosoopical examination of starch are 

 given by Strasburger, Practical Botany, pp. 4-15. 



