70 



Actinic Light 

 Off 



Spinach L«of j»- 



0.7x10' XMc"'x0.5mm"' 

 0.013 xtec xcm 



t t 



Meos. Light 



On , „. 



555-540m/i '-'9''' 



(3m,. Interval) (gaomM) 



50 tac 



Figu re 2. Illustrations of the kinetics of the light-induced cytochrome f 

 oxidation vmder conditions where the measuring light is of sufficiently high 

 intensity to cause rapid oxidation by itself. Time proceeds from left to 

 right. Tlie deflection of both traces with tirae indicates a decrease of ab- 

 sorbaiicy at 555 rjn with respect to 5^0 mu . The sensitivities employed in 

 the tv70 traces are different and are indicated on the diagram. Response 

 tine of the tv/o traces is also different; that of the lower sensitivity has 

 a lower response time corresponding to less than l/2 second, while the trace 

 for the higher sensitivity has a response tirae of approximately 2 seconds. 

 The moment of illtuniiiation with actinic light is indicated, and its wave- 

 lengtli is 680ajJ, A spinach leaf employed in this experiment \7as a mature 

 plant (market spinach) . The rate of absorbancy change on illumination with 

 actinic light is indicated per leaf thickness (0.5 mm) or per centimeter. 

 Experiment 53 A 1. 



Switt Chord Ltof 

 5S5-540m^ 



log I./I'OOOI 



log I./I-0004 



1 



77"> K 



Swiss Chord Leaves Spinach Leaves 



X(m/i) X(m/i) 



680m/i Illumination 



540 550 560 570 



0-1— • 



540 550 560 



ogI./I'0004 



-0.005- 



-SOttc- 



0.005 



FIGURE 3 



FIGURE k 



Figure 3. A ccirpririson of the light response of Swiss chard leaf at 300 

 77^'kV ^Tlie convention in recording is similar ix> that of Figure 2; i.e., 

 t\ro traces of different sensitivities and response speeds. The actinic il- 

 lumination is 680 ran. Time proceeds from left to right; initial rate of ab- 

 sorbancy change is calculated per leaf thickness (O.k mm). Experiment 59-6. 



Figure h. Lot; temperature difference spectra for Sv/iss chard and spinach 

 leaves obtained with the double -beam spectrophotometer, according to the 

 method illustrated by the preceding Figure. A number of similar leaves 

 are selected and illuminated consecutively at Im temperatures. The absorb- 

 ancy changes are indicated per leaf thickness, 680 mm actinic illumination. 

 Experiment 62, 58* 



and 



