152 GROWTH OF PLANTS 



a rapid rate of elongation when removed from the gas. There is an increase 

 in diameter in the growing region near the tip of the seedling, even when it 

 is in a concentration of ethylene that stops all elongation. This forms a 

 knob near the tip, as is shown in Fig. 51, with the high concentration of 

 ethylene. 



A number of later studies 6- s. 69 have been made on the anesthetic action 

 of ethylene, acetylene, propylene, and carbon monoxide upon plants and 

 lower animals. In plants the order of effectiveness of the several gases, 

 that is, the minimum concentration inducing rigor, is the same as for epi- 

 nasty and declination of the pea seedling. It took very high concentrations 

 of these gases to induce rigor in insects and centipedes and the order of 

 effectiveness of the several gases showed no relation to that found for 

 plants. Butylene, which is almost without effect on plants, is the most 

 effective in anesthetizing insects and centipedes, requiring from 5 to 40 

 per cent for the various species. It also partially paralyzes the organisms. 

 Ethylene, which is the strongest anesthetic for plants, along with acetylene, 

 was the least effective on insects and centipedes, requiring a complete 

 atmosphere for anesthesia; 30 to 75 per cent of propylene and 80 to 90 per 

 cent of carbon monoxide were required to anesthetize these organisms. 



It is evident from the facts stated above — and will be borne out by those 

 to be stated later — that besides anesthesia these gases have many other 

 effects on plants, namely, epinasty, proliferation of tissue, abscission, etc. 

 Probably most of these secondary effects can be avoided by using gases in 

 concentrations that produce complete rigor. Epinasty of leaves, however, 

 is induced in concentrations of ethylene that result in complete rigor in 

 other parts of the plant, as shown by time-lapse motion pictures ^ of tomato 

 plants in air and in air containing 2 ppm of ethylene. The photographing 

 was continued 24 hours with the treated plant in the gas, followed by 

 24 hours with the treated plant in ethylene-free air, in order to get both 

 the response and the recovery. The exposures were made 96 times per 

 hour to give a speed of movement on the screen 600 times that occurring 

 in the plants themselves. The top of the check plant was in continuous 

 movement due to unequal rate of growth on the several flanks of the stem; 

 also the leaves on the control plant showed movement during the course 

 of the experiment. Especially conspicuous was the sleep movement during 

 the first night of the experiment. This movement was less conspicuous 

 during the second night due to bad gro^vth conditions furnished by the 

 experiment. 



The movements of the gassed plant must be considered under two heads: 

 the response movements and the recovery movements. Soon after the plant 

 was placed in the anesthetic, the tip of the plant ceased to move and showed 

 no movement during the rest of the exposure. It was in rigor. Moreover, 

 the sleep movement of the leaves did not occur. Instead, noticeable epi- 

 nasty of the petioles began within two to three hours after exposure. The 

 first leaf to show this was the third from the top, followed successively by 



