Nutrition. 



89 



Cut sections of the leaf, and ascertain the location and condi- 

 tion of the substances to which the red color is due. 



Repeat this test with autumnal colors of leaves of maple, oak, 

 or sumac. What differences are to be found between the 

 colors of such leaves as Ainarantus, Coleiis, and Achyranthes, 

 and the autumnal colors? 



92. Arrangements for concentrating rays of light 

 upon chlorophyl layers. — Cut a cross-section of a leaf of 

 Coleus, or any leaf with a velvety surface, and note the outline 

 of the epidermal cells and their effect upon rays of light striking 

 the surface at various angles. Test such leaves with the appa- 

 ratus described in § 90 to ascertain their permeability to light. 

 Make similar tests with some species having a thick leathery 

 leaf. 



93. Exhalation of oxygen by green plants. — Fill a 

 funnel with green sprigs of Philotria, Myriophyllum, or Ca- 

 bomba, and immerse in a beaker of 

 fresh spring water. Fill a small test 

 tube with spring water, and invert it 

 over the small end of the funnel in 

 such manner that no air is allowed 

 to gain access to it. Place the prep- 

 aration in bright sunlight. Observe 

 the rate at which a gas is collected 

 in the uppermost end of the test tube. 

 After an amount sufficient to displace 

 half of the water in the test tube has 

 been collected, close the lower end 

 with the finger, under water, remove 

 the tube, and bring to an upright po- 

 sition. Strike a match, or ignite a 

 splinter of wood in a flame. After a 

 good length of the wood is burning well, extinguish the 

 flame, remove the finger from the end of the test tube, and 



Fig. 59- — Preparation for 

 collecting gases liberated by 

 aquatic plants. After Det- 

 mer. 



