14 NATURE OF CHLOROPHYLL 



absence of chlorophyll in the plastids. Similarly green plants 

 lose their chlorophyll when placed in the dark. This is the 

 principle employed in the blanching of celery. The stalks are 

 surrounded by earth or the light is excluded from them by some 

 other means; chlorophyll disappears from the plastids and fails 

 to develop in the new cells that are formed in the dark. Plants 

 in which the chlorophyll is not developed are said to be etiolated. 

 The plastids are in the cells, however, for if an etiolated seed- 

 ling is removed from the dark to the light the chlorophyll will 

 begin to appear in a few hours. The greening of potatoes when 

 removed from the ground and left in a strong light is a familiar 

 example of this. It is evident that the formation of chlorophyll 

 is closely connected with the action of light. Another impor- 

 tant point regarding the influence of light is the fact that such 

 a food as starch is not usually found in the leaf in the absence 

 of light. This may be easily verified by cutting, the initials of 

 your name in rather large letters in a strip of black paper or 

 smooth tin-foil and fastening the strip in the early morning to 

 the upper surface of a well-sunned leaf of a starch forming plant. 

 Before the sunlight fades remove the leaf from the plant and place 

 it in alcohol. This will dissolve the chlorophyll and the leaf will 

 become quite white in a few hours. Now place the leaf in a 

 tincture of iodine which turns starch to a blue or blue-black color. 

 Wherever the light was excluded from the leaf there is only a 

 pale yellow color but all portions of the sunned leaf show an 

 abundance of starch as revealed by the blue or blue-black colora- 

 tion. Consequently the letters appear black on a yellow back- 

 ground which marks the limits of the strip of paper. No starch 

 can be detected in leaves taken from plants that have been 

 growing in the dark for twenty-four hours. Plastids that do 

 not contain chlorophyll, examples of which are found in the 

 cells forming the white bands or blotches in many variegated 

 plants, do not form starch in the light. It is evident from these 

 facts that the chlorophyll and light co-operate in some way in 

 the formation of starch. It is known that chlorophyll absorbs 

 a certain portion of the sunlight. If a beam of sunlight is 

 caused to pass through a prism it is separated into seven colors, 



