1917] 



DOUBT— ILLUMINATING GAS 



215 



75, and 50 ppm caused the same kind of response, but the degree 

 was lessened somewhat. With ethylene, 8 and 5 ppm caused fall 

 of the older leaves, the younger leaves showing epinasty (fig. 2), 



developed o 

 this amount 



ppm 



leaf fall; 

 response. 





ppm 



o . 1 ppm caused no 



ppm 



Coleus sp. — With 



no leaves fell, and after removal from the cases recovery was com- 



1 



• 



3 



4 



Figs. 3, 4. — Fig 3, Salvia splendens: plant at right was treated with 2 ppm ethyl- 

 ene; after 12 hours it showed distinct epinastic response; plant at left, appearing 

 normal, received 12.5 ppm carbon monoxide; fig. 4, Salvia splendens: control plant 

 and one which has been treated for 18 hours in 1000 ppm illuminating gas; epinastic 

 growth of petioles is clear and leaf blades show a folding together of the sides, which is 

 characteristic of presence of considerable gas. 



plete; 



ppm 



hours exposure; 6000 ppm caused falling of about half the leaves, 

 the older being the ones affected; 



1000 



fall, the younger showed epinasty, and the youngest were unaf- 

 fected; 100 ppm caused slight epinasty of the younger leaves, and 



With ethylene, 5 ppm 



this is close to the limit 



response 



caused the oldest leaves to fall, while the younger, except those at 

 the tip, showed epinasty; 2 ppm caused no leaf fall, and epinasty 

 was slight; 0.2 ppm caused no response. With carbon monoxide 

 12.5 ppm caused no response. 



