CHLOROPHYLL FORMATION 423 



chlorophyll produced per unit volume of these culture solutions was in 

 the ratio of 4.1 to 1. Thus there appears to be a direct proportionality 

 between the nitrogen in the medium and the chlorophyll. These results 

 do not necessarily mean, however, that the nitrogen was used directly 

 for the formation of chlorophyll, because in other experiments organic 

 nitrogen compounds have been shown to serve as sources of nitrogen 

 (cf. Ludwig, 1938; Aronoff, 1950; Salomon et al, 1950). In fact, there 

 appears to be a correlation between protein metabolism and the chloro- 

 phyll content of the leaf (Rombeck, 1943). 



The fact that magnesium is one of the constituent elements of chloro- 

 phyll makes its presence in the nutrient medium obligatory for the con- 

 tinued formation of chlorophyll. Mameh (1915) states that plants of 

 the same species cultivated in solutions containing various quantities of 

 magnesium develop foHage with a chlorophyll content directly propor- 

 tional to the magnesium administered. Fleischer (1935) observed that 

 Chlorella Cornell No. 11 became colorless when it was deprived of mag- 

 nesium, and by variation of the magnesium content of the culture medium 

 in which it was grown, it could be brought to various degrees of greenness. 

 When the magnesium content was increased from 0.02 to 2.0 ppm, the 

 chlorophyll content was increased from 10~^ to 12 X 10~^ g per cubic 

 millimeter of cells. Van Hille (1938) cultivated C. pyrenoidosa cells in 

 nutrient media of various magnesium concentrations. The growth of 

 cells was dependent on the magnesium content of the media, but the 

 chlorophyll content of the cells was about the same in all the cultures. 

 The total chlorophyll produced per unit volume of culture medium 

 increased almost linearly with the magnesium up to about 4 X 10~^ g 

 of magnesium per cubic centimeter. Above this there was no further 

 increase. Bukatsch (1941-1942) found that corn, wheat, and barley 

 plants cultivated in nutrient solutions increased in chlorophyll when the 

 magnesium in the nutrient solution was increased from zero to "normal," 

 but further increase in the magnesium had little or no effect on the 

 chlorophyll. Rissmann (1930) obtained a difference in the reaction of 

 wheat and corn seedlings to magnesium added to their nutrient solutions. 

 This dissimilarity he attributed to the unequal magnesium content of 

 the seeds. 



Rissmann (1930) and Smith (1947) have shown that dark-grown seed- 

 lings contain organic magnesium compounds. Of the total magnesium 

 thus combined in barley seedlings, from about 23 to 46 per cent has been 

 found to be attributable to protochlorophyll (Smith, 1949a). When etio- 

 lated leaves are illuminated, inorganic magnesium is brought into organic 

 combination (cf. Fig. 7-8). 



Many elements that are not constituents of extracted chlorophyll or 

 protochlorophyll affect the formation of chlorophyll. A discussion of 

 their hypothetical involvement in pigment formation is beyond the scope 



