SOME INFRA-RED EFFECTS ON GREEN PLANTS 843 



ABSORPTION BY CHLOROPHYLL AND THE POSSIBILITY OF 



PHOTOSYNTHESIS 



Brown and Escombe (4) have estimated that less than 0.5 per cent 

 of the total energy absorbed by the leaf is used in photosynthesis. This 

 energy is absorbed in certain well-marked absorption bands found in 

 chlorophyll in the visible region. The infra-red absorption of chlorophyll 

 has been studied by Ursprung (21) who has reviewed the older literature 

 on this subject. He found that the pigment in solution absorbed about 

 7.5 per cent as compared with a value of 10 to 17 in the leaf. An iodine 

 solution was used in obtaining infra-red with a Nernst lamp as a source. 

 Gulik (12) using Willstatter's preparations determined the absorption 

 of a and 6 chlorophyll solutions at various wave-lengths to 35,380 A. 

 He found weak absorption in the a component to X10,040 A. The 

 absorption constant for a given concentration at X6460 A was 2.48, 

 at 7730 A it was 0.234, and at 10,040 A it was 0.078. A weaker secondary 

 absorption was found with a maximum at X33,870 to 34,040 A. The b 

 component had little absorption in the near infra-red but had a weak 

 absorption at X33,840 A. Carbon bisulfide was used as the solvent in 

 this work. Since there is an absorption by one of the components of 

 chlorophyll, there is the possibility of photosynthesis in the infra-red 

 region. Ursprung (21) exposed a bean leaf for 40 hours to infra-red 

 using both an ebonite plate and a solution of iodine as a filter to isolate 

 this region. Using the iodine-starch test he showed that some starch 

 was formed under infra-red alone. A photograph of the blackened area 

 is shown. He states that not every experiment of this type succeeds and 

 that a lens must be used which concentrates just the right intensity of 

 energy upon the leaf. He found that the stomata remained closed 

 during the experiment and concludes that the failure of plants to assimi- 

 late more rapidly in the infra-red is due to the closure of stomata, thus 

 limiting the intake of carbon dioxide. Sayre (19, 20) has recently 

 observed that the stomata of Rumex patientia do not open at wave- 

 lengths greater than 6900 A and that chlorophyll is not formed in this 

 region. Arthur (2) found that buckwheat seedlings were not able to 

 produce chlorophyll under infra-red radiation and w^ere identical in 

 appearance and dry weight with those grown in darkness. They grew 

 only at the expense of the food stored originally in the seed. A photo- 

 graph of these seedlings grow'n both in darkness and exposed to the 

 infra-red region of sunlight is shown in Fig. 1. He also found that when 

 such seedlings were grown under incandescent-filament lamps operating 

 at low^ and high efficiencies, the dry weight of tissue produced was pro- 

 portional to the energy in the visible region and independent of the 

 proportional part of infra-red. There is the possibility that plants grown 

 with the visible energy of sunlight in a greenhouse during the day might 



