YIELD OF PHOTOSYNTHESIS IN ALTERNATING LIGHT 



1439 



with the higher land plants can be obtained also with stomata-free lower 

 plants (green or blue algae). These plants, too, grew particularly slowly 

 in light mth an alternation frequency of 1/min., and much better at t = 

 0.25 or 0.08 second, or t > I minute. More recent experiments on the 

 growth of unicellular algae {Chlorella) in intermittent Hght gave a similar 

 result (c/. part B, pp. 1476-1477). 



Fig. 34.3. Effect of intermittent illumination, with equal light and dark pe- 

 riods, on photosynthesis in wheat plants (after McAhster 1937). Arrows indicate 

 beginning and end of illumination. Points represent spectroscopic CO2 deter- 

 minations in half minute intervals. 



We conclude from these experiments that the inertia of the stomata can 

 be, at best, only a contributing cause of the inhibition of plant growth by 

 alternating light with a frequency of the order of 1/min. Comparison of 

 figure 34.1 with the figures in chap. 33 makes it Hkely that the main cause 

 of this behavior is induction, which is almost fully developed after 1 minute 

 of darkness, and permits only little photosynthesis in the first minute of 

 subsequent illumination. 



Figure 34.3 shows that according to McAlister (1937) the average 

 rate of consumption of carbon dioxide by wheat plants also is slowest at 



