io6 Elementary Plant Physiology. 



a blue reaction when a drop of it is treated with iodine solu- 

 tion. Set aside part of the starch solution as a control, and 

 add the filtered extract of barley, which contains a solution 

 of the enzyme diastase, to the bulk of the solution. Take a 

 sample of the solution fifteen minutes later, and note the 

 iodine reaction. Repeat a half hour, an hour, two hours, and 

 three hours later. What is the fate of the starch ? Compare 

 taste of the solution at beginning and close of the experiment. 

 Repeat the test, using ungerminated seeds of barley in one 

 series, and fresh leaves of barley, finely ground, in another, 

 and compare results. 



112. Digestive action of scutellum of corn The 

 enzymes play a very important part in digestion, and special 

 layers for the secretion of these substances are to be found in 

 the aleurone layers of seeds of grasses, and also in the outer 

 layer of the embryo. The action of the digestive secretions 

 may be demonstrated as follows : grate the white portion of 

 a potato into a smooth pulp, and fill the cavities in a dozen 

 culture slides. Dissect out the embryos of an equal number 

 of seeds of corn that have been in a germinator for two 

 days. Lay one of these embryos on every one of the masses of 

 grated potato, and put all of the preparations in a moist 

 chamber, which should be kept at about 40 C. A control 

 slide with grated potato alone should be added to the 

 series. Examine some of the grated potato with a magnifi- 

 cation of about 400 to 500, and note the appearance of the 

 starch grains. Note microchemical reaction with iodine. 

 Now apply the iodine test to a separate slide at the end of 

 every hour. What is t'he fate of the starch grains as indi- 

 cated by the color reactions and by the microscopic exami- 

 nations ? 



Test some of the fresh potato for sugar, and some of the 

 material treated several hours with Fehl ing's solution. (See 

 " Practical Plant Physiology.") 



