THE WORK OF LEAVES 181 



Can you explain these differences of structure as due 

 to differences in function ? What is the function of the 

 foliage-leaves? Remove the foliage- leaves (a) from 

 some young plants which have not yet exhausted the 

 supply of food in their seed-leaves; (b) from. some older 

 plants in which this supply is exhausted and from 

 which the seed-leaves have fallen away; in each case 

 have control plants for comparison. Does the removal 

 of the leaves check the growth? In which of the two 

 cases (a) or (6) is this most apparent? Does the result 

 indicate that the foliage -leaves, like the seed-leaves, 

 nourish the plant? 



Do the foliage-leaves, like the seed-leaves, contain 

 food? Remove some foliage -leaves from a healthy, 

 vigorous plant, preferably one which grows out of 

 doors, with a good exposure to sunlight (a Nasturtium 

 is excellent for this purpose) . Remove some of the 

 leaves at sundown. Boil them in water as soon as 

 removed and place them in alcohol; let them remain 

 in it until the green coloring matter is extracted. 

 When this is accomplished (twelve to twenty-four 

 hours is ususually sufficient) , rinse in water, and place 

 them in watery iodine solution. Do you find starch 

 present? (The other tests mentioned on pages 164 and 

 165 may also be made; the sugar test should be made 

 on sap expressed from the fresh leaves; the test for 

 oils and fats on leaves dried without being placed in 

 alcohol.) 



