CHEMISTRY OF PLANT GROWTH 245 



the upper leaves become yellow, and finally the husk be- 

 comes yellow and inactive. Chlorophyl is one of the 

 principal agents which takes an active part in plant growth, 

 and whenever chlorophyl is destroyed, plant growth is 

 checked. 



Experiment 68. Extracting chlorophyl from leaves. Place in 

 a test-tube, 0.5 gram of dry, green leaves. Add 10 cc. alcohol, shake 

 vigorously and, after the alcohol is colored green, filter off the 

 solution, and evaporate to dry ness at a low temperature on the 

 water-bath. 



Questions. (i) Describe the appearance of the chlorophyl 

 residue. (2) What is chlorophyl ? (3) Of what is it composed? 

 (4) What other solvents could be used in place of alcohol. 



346. Function of Chlorophyl. The chief function of 

 chlorophyl, aided by protoplasm, is the production of 

 starch and other organic compounds in the cells of plant 

 leaves. Chlorophyl alone cannot perform this function, 

 but must be associated with, and aided by, protoplasm. 

 Minute starch grains are sometimes found within the 

 chlorophyl grains. The actual growth of starch within 

 the chlorophyl body can be observed with the microscope. 

 No other compounds have been found so organically con- 

 nected with the chlorophyl grains as starch. If a plant 

 is placed in darkness, both the starch and the coloring- 

 matter in the plant cells disappear. The plant cell is the 

 chemical laboratory in which the various organic com- 

 pounds, as starch, sugar and proteids, are elaborated. 

 From the cells in the leaves, they are transported to other 

 parts of the plant as the seeds, roots or tubers, where they 

 are stored up and serve as reserve food. 



347. Production of Organic flatter. By the joint 



