PHYSIOLOGICALLY ACTIVE GASES 153 



the leaves below on the gro\\nng part of the stem and then by the two tip 

 leaves. Several hours later the older leaves on the non-elongating part of 

 the stem showed epinastic movement. The leaves on the growing part of 

 the stem had completed their epinastic movements Avithin 8 or 10 hours 

 and the leaves on the more mature part of the stem withm 15 or 20 hours. 

 Younger leaves curved throughout the length of the petioles, while in the 

 older leaves the curvature was limited to the base of the petioles. After 

 the leaves had come into equilibrium by epinastic response, all movement 

 in them ceased for the duration of the exposure. The whole plant was in 

 rigor. Two or three hours after the gassed plant was put into ethylene- 

 free air, the recovery from the epinasty began and continued in about the 

 same order and, for the younger leaves, with nearly the same speed as the 

 response. The leaves on the growing part of the stem showed complete 

 recovery to the original position, while the older leaves showed only partial 

 recovery. Also within two or three hours after removal of the plant from 

 the anesthetic, vigorous movement started in the tip and continued 

 throughout the period. The tip of the plant recovered completely from 

 the rigor. 



The time-lapse pictures of the sunflower showed similar behavior. Com- 

 parable time-lapse pictures were made of the sensitive plant, using 0.5 per 

 cent of CO as the anesthetic. Complete anesthesia was induced in this 

 plant, and complete recovery occurred after removal from the gas, as shown 

 by loss of power to respond to contact stimuli while in the gas and recovery 

 of this power after removal from the gas. When this plant is anesthe- 

 tized, however, there is a slow, non-correlated movement of the individual 

 leaves and leaflets that gives the plant a disorganized appearance (Fig. 58). 

 The movements of the leaves and leaflets of this plant are brought about 

 by changes in osmotic pressure in cells of the pulvini at the base of leaves 

 and leaflets, and not by growth. The slow, non-correlated movements in 

 the leaves and leaflets in the anesthetized plant would have been entirely- 

 overlooked if it had not been for the time-lapse pictures. 



When plants are exposed to ethylene in concentrations below the rigor- 

 producing dosage, the rate of growth is retarded, with or without other 

 secondary effects, depending upon the kind of plants treated and the con- 

 centration of the gas used. A study was made of the effect of low concen- 

 trations of ethylene (1 part to 10 million and 1 part to 25 million of air) 

 on the growth rate of seeds and seedlings of wheat, buckwheat, tomato, 

 clover, and corn growing in soil in pots. These experiments were carried 

 out in two continuous and regulated air-flow Wardian cases in a special 

 greenhouse. This apparatus will be illustrated and described in the next 

 chapter. The rate of air flow through each chamber was 200 cubic feet per 

 minute. By means of a calibrated capillary flowmeter a measured amount 

 of ethylene was added to the air passing through one flow-chamber to give 

 the concentration of ethylene desired. Six pots each of seeds and seedlings 

 of each kind of plant were used in the control and treated chamber. 



