88 Elementary Plant Physiology. 



repeatedly. Press out the water from the fragments, and return 

 to flask. Cover with alcohol, and set in a dark place until the 

 following day. Now pour some of the extract into a narrow 

 test tube, and hold up to the light. The solution appears green, 

 but the edges show a blood-red color, due to the fluorescence 

 of chlorophyl, which has the power of changing the length of 

 the waves of light in such manner as to give the red color. 



If a portion of the solution is examined by the aid of a spec- 

 troscope, it may be seen that some of the rays are absorbed. 

 The absorbed rays are converted into other forms of energy in 

 the plant and used to perform the work of food formation. 



89. Formation of chlorophyl in light and dark- 

 ness. — Germinate some seeds of pine, and also some acorns, 

 in a dark chamber. Note the formation of chlorophyl in seed- 

 lings of the conifers in darkness. After the seedling oaks have 

 appeared and are a few centimeters in height, remove to a 

 shaded corner of the laboratory, and follow the appearance of a 

 green color. 



go. Absorption of light by tissues of plants. — 

 Secure two shot-gun cartridge shells, one of ten caliber and the 

 other of twelve. If uncapped, the closed end will show a small 

 perforation. Cut circular pieces from the leaf blades of any 

 convenient species, and fit over end of smaller shell. Slip the 

 larger shell over the smaller one, and thus hold the section of 

 leaf between the closed ends of the two. Appl)' the eye to the 

 open end, and direct toward a strong light. Note the amount 

 of light that penetrates the leaf. Add one or more sections of 

 the leaf to the preparation, and test permeability to direct rays 

 of sun. How many layers of leaf blades will sunlight pene- 

 trate? It will be interesting to test the outer layers of young 

 twigs and bark of other plants in the same manner. 



91. Red color in leaves — Boil a number of red leaves 

 of Amarantus (cockscomb) in water, and note the extraction 

 of the coloring matter. Do red leaves contain chlorophyl? 



