442 BOTANICAL GAZETTE [NOVEMBER 
capable of responding to even considerably lower concentrations 
than any yet tried. The least delicate of the reactions, the pro- 
liferation and exudation at leaf scars, usually appears in concen- 
trations of about one part ethylene to 50,000 of air; while leaf 
fall and especially the starting of abscission layers may appear in 
concentrations as low as one part ethylene to 500,000 of air, or 
even one part ethylene to 1,000,000 of air. The nastic drooping 
of the youngest well developed leaves and the folding down of the 
laminae of the young leaves are the responses one must depend 
on for extremely low concentrations. 
The accompanying table (table I) will serve to show the method 
of recording the reactions, and also how close is the parallelism 
between the ethylene and the illuminating gas under the conditions 
of concentration named above. 
In conclusion it may be stated that the castor bean plant has 
proved capable of giving an easily observed response to extremely 
small amounts of ethylene; and on account of this fact the plant 
seems particularly useful for the detection of harmful gaseous 
impurities? in the air of laboratories and greenhouses. 
The writer gratefully acknowledges the many valuable sug- 
gestions of Dr. WILLIAM CROCKER. 
UNIVERSITY OF CHICAGO 
?Tt would not be of value for suck i ities as are not active in inducing 
this respon$e, but ethylene, though in "paall amounts, is probably the most harmful 
and generally present of any laboratory air impurity. 

“ta, eee 
Specials 
