CHLOROPHYLL FORMATION 



417 



phyll is transformed to chlorophyll. This involves no change in total 

 ether-soluble magnesium. But inasmuch as illumination more than 

 doubles the quantity of magnesium extractable with ether, it must be 

 concluded that new organic magnesium compounds are formed by photo- 

 chemical action (cf. Fig. 7-8). It is not known that these compounds 

 are precursors of chlorophyll, but their nature suggests this possibility 

 (Smith, 1949a). 



Table 7-5. Regeneratiox of Protochlorophyll in Dark-grown Corn Seedlings 



4. EFFECT OF TEMPERATURE ON CHLOROPHYLL FORMATION 



AND ACCUMULATION 



A systematic study by Sachs (1865) showed that, within limits, the 

 rate of greening increased with the temperature, that there w^as a thresh- 

 old temperature below which each species of plant would not green, and 

 that this threshold differed with the species. 



Table 7-6. Effect of Temperature on the Accumulation of Chlorophyll 

 IN Triticmn ferrugineum after Various Lengths of Illumination 



(Lubimenko, 1928.) 



Lubimenko (1928) followed the rate of chlorophyll formation at dif- 

 ferent temperatures. His results for Triticum ferrugineum are given in 

 Table 7-6. After 2 hr of illumination a small quantity of chlorophyll is 

 formed at all temperatures. At 0°C the quantity of chlorophyll is not 

 increased by further illumination; at 4°C it remains about constant for 

 8 hr and then increases at an accelerated rate; and at 11° and 20°C it 



