172 LIVING PLANTS 



its physical properties may be gained. If 

 such a ra3^ of light is passed through a prism 

 and spread out on a screen, it may be seen 

 that there are several large intervals or dark 

 bands in the spectrum. The rays of light 

 which would have occupied these spaces have 

 been absorbed by the chlorophyll, and con- 

 verted into heat and other forms of energy. 

 This energy is directly available to the proto- 

 plasm containing the chlorophyll, and by 

 means of it the synthesis of complex substances 

 may be accomplished. Moreover, the amount 

 of synthesis accomplished by plants exposed 

 to separate portions of the spectrum will be 

 directly proportional to the amount of that 

 portion which can be absorbed and converted 

 into useful forms of energy. The amount of 

 synthesis is shown to be greatest in the red 

 rays between B and C, where the most com- 

 plete absorption takes place. 



Chlorophyll is a very complex and highly 

 unstable substance, and during the absorp- 

 tion of light it is slowly broken down, but or- 

 dinarily it is rebuilt by the protoplasm as 

 fast as it is decomposed. If, however, the 

 chlorophyll and the leaf containing it are ex- 

 posed to a light of such intensity that the 

 chlorophyll is decomposed faster than it can 

 be rebuilt, then damage must ensue, which if 

 sufficiently extensive will result in the death 



