RESPIRATION AND OTHER FORMS OF METABOLISM. 49 



lain dish, whereupon they will be colored a deep blue except in 

 shaded portions. Since, substantially, starch-formation in the leaf 

 proceeds by day only, and the solution and translocation at night 

 as well, the places exposed to the sunlight contain enough starch to 



Fig. 43. b 





a, Tropseolum leaf to which are attached two pieces of cork to prevent pho- 

 tosynthesis. (Detmer.) b, same after removal of cork, treated with 

 iodine. 



give the microscopic reaction with iodine. It was taken away from 



the shaded places at night, however, and could not be replaced. 



<Fig- 43-) 



39. Changes in Color. — Many changes in the chemical com- 

 position of substances in the plant are accompanied by corre- 

 sponding changes in color. (See Chlorophyll, Par. 30.) Flow- 

 ers which are blue when fully opened were originally red in the 

 bud. The sap was acid at first and became alkaline as the result 

 of metabolic changes. Leaf-colors offer similar conditions, 

 although the changes in color here are sometimes due to the 

 oxidation of chlorophyll and other coloring matter in the cells. 

 EXPERIMENT 58. 



RELATION OF RED AND BLUE COLORS OF FLOWERS. 



Immerse a leaf of Begonia bearing red hairs, for a short time in 

 a weak solution of ammonia. The hairs become blue. Place a 

 blue petal of Myosotis in a i^ solution of acetic acid. It becomes 

 reddish. Express the sap from a handful of petals of Roses or 

 Peonies. Collect in a test-tube and add a few drops of ammonia. 

 A blue color results. Add some acid. The red color is restored. 

 Observe the different colors assumed by leaves in the autumn. 



