iq8 



BOTANICAL GAZETTE 



SEPTEMBER 



tight; and enough ethylene 1 admitted to make the concentration 

 about o.oooi per cent by volume. Both control and treated por- 

 tions were then allowed to continue 

 development for 72 hours under 

 the same conditions (that is, of 

 moisture, temperature, and dark- 

 ness), except for the ethylene in 

 one. At the end of this period 

 the epicotyls were collected for 

 experimentation. The total cul- 

 ture period was 9 days. 



The epicotyls of the control 

 seedlings, at the time of collection, 

 were 8-1 1 cm. in length and verti- 

 cal and straight. But the ethy- 

 lene treated seedlings showed the 

 well known "horizontal nutation" 

 (Neljubow 25) or "triple re- 

 sponse" (Knight and Crocker); 

 that is, the epicotyls were only 

 3-5 cm. long, swollen, and had 

 assumed horizontal or nearly hori- 

 zontal positions. The difference 

 in appearance between the ethylene treated and the untreated 

 seedlings is shown in fig. 1. Certain histological differences are 

 shown by the drawings of fig. 2. 



Fig. 1. — Etiolated seedlings of the 

 sweet pea, showing the stage of 

 development at which the epicotyls 

 were taken for experimentation: A, 

 normal; B, ethylene treated, showing 

 the "triple response"; Xi- 



Methods and experimentation 



The present attack of the problem on the effects of ethylene has 

 been made through a study of the following questions: (1) chemical 

 composition, (2) acidity, (3) osmotic pressure and permeability, 

 and (4) respiration. A decided emphasis has been laid upon the 

 chemical phase of the problem. 



1 The ethylene used in these experiments was prepared by dropping ethyl alcohol 

 into syrupy phosphoric acid at a temperature of about 215° C. The final dilutions 

 of ethylene were made from a stock ethylene-air mixture containing 2 . 5 per cent 

 ethylene. 



