154 



GROWTH OF PLANTS 



FiGTJRE 58. The anesthetic effect of carbon monoxide on. plants. A, Mimosa pudica 

 control. B, The same plant as "A" after exposure to one per cent carbon monoxide for 

 18 hours. Note the change in the normal equilibrium position of the leaves and the 

 disturbance of normal correlation. 



Fig. 59 and Table 19 show the effect of these low concentrations of ethylene 

 upon the growth rate of seeds and seedlings. For the illustration a typical 

 pot was selected in each case and photographed, and for the table all 

 seedlings of each kind and lot were measured at the beginning and end of 

 the experiments and the average elongation during the experiment cal- 

 culated. Examination of the figure shows that 1 part of ethylene to 

 10 million of air causes a marked reduction in growth rate and 1 part to 

 25 million an evident reduction. There is no killing of tissue; the growth 

 inhibition is an incipient anesthetic effect. The table shows that 1 part of 

 ethylene to 10 million of air reduced the rate of elongation by the following 

 percentages: clover, 50; tomatoes and buckwheat, 40; and wheat, 25. 



Table 19. Per Cent Inhibition of Growth in Length by Ethylene. 



1 part of ethylene to 10 million of air. Continuous fumiga- 

 tion for 4 weeks 



Clover 

 Tomatoes 



50 

 40 



Buckwheat 

 Wheat 



40 

 25 



