1915] HARVEY & ROSE—ILLUMINATING GAS 35 
swollen zone longer and not so thick; more growth of hypocotyl; 
(3) concentration 1: 100,000; little if any effect. 
_ With ethylene.—(1) Concentration 1:12,500; short swollen 
knob between stem and root; growth greatly retarded; (2) con- 
centration 1:250,000; swollen knob longer and not so thick as in 
(1); (3) concentration 1:2,500,000; little if any effect. 
The response shown by the tomato seedling differs very mark- 
edly from that shown by the radish and mustard seedlings. While 
the roots of the radish and mustard seedlings show a coiling and 
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: Fic. 2.—Sections of the root of tomato seedlings: A, control; B, treated with 
illuminating gas; x18 
bending similar to those of the Vicia Faba, in addition to a slight 
swelling of the hypocotyl, the only response shown by the tomato 
seedling is a decided swelling of the hypocotyl and root at the point 
where the two join. With the tomato seedling the parallel experi- 
ments with ethylene again give some evidence that the toxic effect 
recorded for illuminating gas is due to the ethylene constituent 
of that gas. 
The results recorded above for Vicia Faba, radish, and mustard 
Show that injuries to roots may readily be brought about by placing 
them in an atmosphere containing small amounts of illuminating gas 
