62 



PHYSIOLOGY. 



150. To test this let us perform an experiment which is often made. We 

 tnay take a plant such as a garden tropaeolum or a clover plant, or other land 



Leaf of coleus showing green and white 

 areas, before treatment with iodine. 



Similar leaf treated with iodine, the starch re- 

 action only showing where the leaf was green. 



plant in which it is easy to test for the presence of starch. Pin a piece of 

 circular cork, which is smaller than the area of the leaf, on either side of the 



leaf, as in fig. 53. Place the 

 plant where it will be in the 

 sunlight. On the afternoon 

 of the following day, if the sun 

 has been shining, we may 

 remove the corks and test for 

 starch, using the entire leaf, 

 by Schimper's method. Or 

 the method described in 146 



Fig " 53> c Fig " 54 : . may be employed. The part 



Leaf of tropaeolum Leaf of tropaeolum treated 



with portion covered with iodine after removal of covered by the cork Will not 

 with corks to prevent cork, to show that starch is re- . , , 



theformation of starch, moved from the leaf during the give the reaction for starch, 

 (After Detmer.) night. as snO wn by the absence of the 



bluish color, while the other parts of the leaf will show it. The starch 

 which was in that part of the leaf the day before was dissolved and removed 



