EFFECT OF INTERMITTENT SKY LIGHT 93 



The variations of photosynthetic activity under inter- 

 mittent illumination of different periods of sky light are 

 clearly shown in the series of horizontal records (fig. 27). 



(1) The first line is the record under continuous light, 

 there being 8 equal spaces representing 8 bubbles in 

 the course of 160 seconds ; that is, 20 seconds per bubble, 

 or 4 bubbles in 80 seconds, the rate being 



_i X 60 X 60 = 180 bubbles per hour. 

 80 



(2) The second line is the record with an inter- 

 mission-period of 0-5 second. There are now 4 bubbles 

 in the course of 160 seconds, or 40 seconds per bubble. On 

 account of alternating light and darkness, the total ex- 

 posure to light was 80 seconds, and the rate of photosyn- 

 thetic evolution of oxygen was practically the same as 



before, i x 60 X 60 = 180 bubbles per hour. Careful 

 80 



inspection of the record shows, however, that the fourth 

 bubble occurred earlier, the dotted record being slightly 

 to the left of the last dot in the first line. I will presently 

 refer to this characteristic in greater detail. 



(3) At an intermission-period of 1 second, the bubbles 



appeared at intervals of 41 -7 seconds, i.e. for actual exposure 



at -n „ , , • 3600 



to light of * — '- = 20-85 seconds, the rate being — g- 



= 172-8 bubbles per hour. There is here a distinct 

 diminution in the rate, due to intermission. 



(4) The fourth line shows the effect of 2 seconds' inter- 

 mission, the bubbling-period being increased to 47 -6 seconds 

 and the photosynthetic activity reduced to 152-2. 



(5) At an intermission-period of 3 seconds, the bubbling- 

 period was increased to 51 seconds and the activity reduced 

 to 141 -2. 



(6) The sixth line is the record of the effect of 5 seconds' 

 intermission-period. The period of bubbling was increased 

 to 55 seconds and the activity decreased to 130-8. Up to 

 this point there had been a continuous increase in the 



