194 COLLEGE BOTANY 



sunlight is the form of energy by which the plant is able to manu- 

 facture carbohydrates; the force which runs the factory. It is 

 absorbed by the chlorophyll of the plant cells and transformed 

 into available forms of energy. This process is not well under- 

 stood. However, if the chlorophyll be extracted from leaves 

 by boiling in water and then soaking in alcohol and the resulting 

 solution studied with the spectroscope, it will be found that the 

 red and blue rays are absorbed, while most of the green rays 

 pass through the solution. This indicates that the red and blue 

 rays furnish the energy and that leaves appear green because it 

 is the green rays only that come to our eyes. 



Composition of Chlorophyll. We do not know the exact 

 chemical composition of chlorophyll, but we do know that it 

 contains carbon, hydrogen, oxygen, nitrogen and magnesium and 

 that it is made up of several pigments, of which chlorophyllin 

 (or cyanophyllin) is the most important. Carotin is always 

 found mixed with the chlorophyll and was for a long time sup- 

 posed to be a part of it, but is now believed to be independent. 

 Carotin is also found in other parts of the plant, such as yellow 

 flowers and fleshy roots. The chlorophyll and carotin may be 

 very readily separated and studied by mixing the chlorophyll 

 extract with benzene (four parts of the extract to one part 

 of benzene), thoroughly shaking and allowing to stand for 

 a time; the benzene rises above the alcohol. The benzene will 

 contain the chlorophyllin, which is bluish green, and the alcohol 

 will contain the yellowish carotin. Although the chlorophyllin 

 is probably a distinct pigment, it is doubtful if it exist indepen- 

 dently in nature. It appears to be closely related to the haemo- 

 globin of the blood, although the relationship is not well under- 

 stood. The carotin is much more abundant than the chloro- 

 phyllin. x It exists independently of the chlorophyllin and in 



