OCCURRENCE OF CARBOHYDRATES IN PLANTS 41 



8. Boil in water, in a test-tube, portions of the above- 

 mentioned parts of plants, and proceed with the 

 starch test, as above outlined. Record the experi- 

 ment as usual. Be careful to distinguish between 

 your observations and your inferences. 



Experiment 20. Microchemical tests for starch. 



9. If time permits of individual tests by the student, 

 microchemical tests may be made by mounting in 

 water, on microscopic slides, small portions of, 

 first, commercial starch; second, material scraped 

 from any soaked seeds (e.g., corn, bean), a potato- 

 tuber (a stem), any convenient fleshy root, in each 

 case observing (and drawing) the shape, surface- 

 markings, and characteristic groupings of the starch 

 grains, then running under the cover-glass a drop 

 of iodine solution, and observing the color reaction. 



Experiment 21. To see if there is starch in leaves. 



10. Extract the chlorophyll from leaves of nasturtium, 

 bean seedling, or other convenient large-leaved 

 plant, by placing the leaf first in hot water to facili- 

 tate the extraction; second, in hot alcohol, or, after 

 they have been dipped in hot water, the leaves may 



.be left in cold 80 per cent, alcohol until the following 

 class period. 



11. Describe the effect of the alcohol on the color of the 

 leaf, and state your inferences as to the solubility 

 of chlorophyll. 



12. Place the leaf in a watch-glass, and irrigate it 

 with iodine solution. After a few moments pour 

 off the iodine, and observe the color of the leaf. 

 This last observation is often made more striking 

 by placing the leaf on a small piece of glass, and 

 holding it to the light. State your inferences from 

 this observation. 



