1915] HARVEY—ETHYLENE 197 
caused an initial outburst, afterward a falling off; and strong 
doses caused depression from the beginning. THopay (33) has 
made some careful determinations, both of CO, releasal and of 
O. 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 (Tropaecolum) 
O, absorption was depressed more than the CO, output. But in 
leaves containing tannin (Pinus and Helianthus) the situation was 
reversed; there was an initial rapid absorption of O, which soon 
fell to a level somewhat above the CO, 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 Knicut 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 (23048 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 2cm. The filter paper was then taken off the 
seedlings and 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 225 liters’ capacity; the lid sealed gas- 
