i 9 i 5 ] HARVEY— ETHYLENE iqj 



caused an initial outburst, afterward a falling off; and strong 

 doses caused depression from the beginning. Thoday (33) has 

 made some careful determinations, both of CO, releasal and of 

 2 absorption. Weak concentration of chloroform accelerated 

 both processes to an equal degree, hence the respiration ratio 

 remained the same. When the doses were considerably stronger, 

 respiration was retarded, but the correlation between the two 

 processes was broken up. In leaves without tannin (Tropaeolum) 

 0, absorption was depressed more than the CO, output. But in 

 leaves containing tannin (Piuus and Iliiiaiillius) the situation was 

 reversed; there was an initial rapid absorption of 2 which soon 

 fell to a level somewhat above the C0 2 production. 



Material 



The sweet pea seedling was chosen as experimental material 

 for the present study, largely because it is so sensitive to toxic 

 substances, and on account of the general interest surrounding its 

 characteristic responses. 



Etiolated seedlings were used throughout the experiments. 

 The seeds were purchased under the trade name Gladys Unwin 

 (Vaughn's Seed Store). The cultural methods employed have 

 been described by Knight and Crocker (20), although some minor 

 changes were necessary in order to care for large cultures. The 

 methods are briefly outlined below. 



The seeds were scratched with a file (to secure quick and uni- 

 form germination), soaked for 12 hours in distilled water, and 

 germinated on wet filter paper. When the hypocotyls had become 

 3-7 cm. long the seeds were sowed upon wet absorbent cotton in 

 large pans (2X30X48 cm.) and covered with a layer of wet filter 

 paper. They were allowed to develop in absolute darkness at a 

 temperature of 21-24° C., until the epicotyls had reached an average 

 length of about 2 cm. The filter paper was then taken off the 

 seedlings ami the culture equally divided into two portions, one 

 for treatment with ethylene, the other for control. The entire 

 culture usually consisted of 12 pans, each containing about 250 

 seedlings. The portion for ethylene treatment was transferred 

 to a galvanized iron box of 223 liters' capacity; the lid sealed gas- 



