CHLOROPHYLL FORMATION 409 



mation of chlorophyll. Whether the relative activities of the different 

 spectral regions have the order red > blue > green, as several investi- 

 gators propose (Lubimenko, 1927; Monteverde and Lubimenko, 1911; 

 Guerrini, 1941), or red > green > blue, as found by others (Sayre, 1928; 

 Rudolph, 1934; Strott, 1938), is in doubt. The order may depend on 

 the plant at the time of measurement, because great variation can occur 

 in the effectiveness of the blue region (cf. Fig. 7-11). 



It is uncertain how far the activity can extend into the ultraviolet 

 (cf. Guillemin, 1857; Reinke, 1893; Wiesner, 1877; Stoklasa, 1911; Sayre, 

 1928; Weissenbock and Neubauer, 1940). Wiesner found greening up to 

 about 397 m^, whereas Sayre (1928), Stoklasa (1911), and Weissenbock 

 and Neubauer (1940) place the limit at about 300 m^i. 



Absolute limits cannot be given to the wave lengths of radiation active 

 in' chlorophyll formation, but the effective range is approximately from 

 680 to 300 m^. 



The action spectrum for the formation of chlorophyll was first meas- 

 ured quantitatively by Schmidt (1914), who illuminated etiolated corn 

 leaves with various spectral regions isolated by means of calibrated 

 colored filters. He assumed the wave length of irradiation to be the 

 middle of the filter's transmission band. He calculated the incident 

 energy from the hght intensity and the time necessary to develop the 

 first spectroscopically detectable chlorophyll. The reciprocal of this 

 energy he considered as proportional to the effectiveness of the different 

 wave lengths. Schmidt's results follow: 



Wave length, m/< 677.5 640.0 620.0 592.5 567.5 527.5 505.0 477.5 450.0 432.5 



Relative efTectivene.ss 2,95 123.1 17.25 67.5 116 5 5.92 1.2 3.22 96.15 13.40 



Schmidt found three peaks of effectiveness at wave lengths 640, 567, and 

 450 m/x. The relative efficiencies of the radiation were in the order given. 



Frank (1946) measured the effectiveness of 16 regions of the spectrum 

 for the production of chlorophyll in oat seedlings. She used combinations 

 of hght filters to isolate the various spectral regions, and to each filter 

 combination she assigned a dominant wave length. She employed an 

 illumination period of 5 hr with an energy flux suflScient to form a definite 

 quantity of chlorophyll. The chlorophyll formed was extracted and was 

 measured spectroscopically. The effectiveness was then calculated as the 

 reciprocal of the relative number of quanta required in different parts of 

 the spectrum to produce the same quantity of chlorophyll. The effective- 

 ness curve obtained is given in Fig. 7-10 along with the absorption curve 

 of protochlorophyll in ether (cf. Smith, 1948). Peaks of effectiveness, 

 in the order of their efficiency, were found at 445, 645, 575, and 545 m/x. 



Koski et al. (1951) measured the action spectra for the transformation 

 of protochlorophyll to chlorophyll a in dark-grown normal and albino 

 corn leaves. The leaves were illuminated with various wave lengths of 



