r 9IS ] HARVEY Sf 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 



Fig. 2. — Sections of the root of tomato seedlings 

 illuminating gas; XiS. 



. 1. control; B, treated with 



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 



