CHLOROPHYLL AND ENERGY 



167 



chlorophyll involve the fixation of the magnesium and 

 the formation of this cycle. 



CH, 



CHa 



II 

 CH 



CH3 



\- 



= CH- 



-CH=CH, 



NH 



/ N 

 CH 



NH N 



/\= CH - ^• 



CH, 



CHa 



I 

 CH2 



I 

 COOH 



I 

 CH2 



I 

 CHa 



CH 



CH, 



COOH 



Protoporphyrin 



Up to this point the process can be accomplished without 

 Ught, but at the last stage light is necessary, at least for the 

 higher plants, although certain algae and even certain conifer 

 seeds can pass through it in the dark. 



This last stage seems to consist in a reduction — in the 

 acquisition of 2 atoms of hydrogen by a group — CH=CH2, 

 which is situated in position 4, at the top right-hand side of 

 the formula, and which becomes — CH2 — CH3. Proto- 

 chlorophyll has accumulated in the dark and as soon as Ught 

 appears the transformation is accomphshed; in less than two 

 minutes chlorophyll is formed. 



As one would expect, the different wave-lengths of light 

 do not all have the same influence and the most effective are 

 those which chlorophyll absorbs best. Nevertheless, a small 

 difference may be noticed; the longest wave-lengths seem to 

 be relatively more efficacious. Simdnis made a comparative 

 study of the formation of the chloroplasts in red light and in 



