DIGESTION 



79 



113. Excluding light 

 from part of a leaf. 



114. The result. 



in the sunlight again. After a niorning of bright sun- 

 shine dissolve the chlorophyll in this leaf with alcohol; 

 then stain the leaf with the iodine. Notice that the leaf 

 is stained deeply in all 

 parts except in that part 

 over which the cork was 

 placed, as in Fig. 114. 

 There is no starch in the 

 covered area. 



167. Plants or parts 

 of plants which have de- 

 veloped no chlorophyll can 

 form no starch. Secure 

 a variegated leaf of co- 

 leu s, ribbon grass, gera- 

 nium, or of any plant showing both white and green areas. 

 On a day of bright sunshine test one of these leaves 

 by the alcohol and iodine method for the presence of 

 starch. Observe that the parts devoid of green color 

 have formed no starch. However, after starch has once 

 been formed in the leaves, it may be changed into solu- 

 ble substances and removed to be again converted into 

 starch in other parts of the living tissues. 



168. DIGESTION. — Starch is in the form of insoluble gran- 

 ules. Whenever the material is carried from one part of the 

 plant to another for purposes of groivth or storage, it is 

 made soluble before it can be transported. When this 

 starchy material is transferred from place to place, it is 

 usually changed into sugar by the action of a ferment. 

 This is a process of digestion. It is much like the change 

 of starchy foods to sugary foods by the saliva. 



169 . DISTRIBUTION OF THE DIGESTED FOOD.— After being 

 changed to the soluble form, this material is ready to be 

 used in growth, either in the leaf, in the stem, or in the 

 roots. With other luore complex products it is then r^'-- 



