84 



The Plant World. 



able, therefore, that these constituents play no part in determin- 

 ing the toxic limit of illuminating gas. The absorption of hydro- 

 gen sulfid and sulfur dioxid does not modify the toxicity of the 

 gas. This leaves, then, ethylene, the higher homologues of 

 ethylene and acetylene, and certain aromatic sulfur compounds 

 to account for the toxicity of the gas. All these substances 

 except ethylene exist in very small percentages in illuminating 

 gas. All evidence in the following experiments also points to 

 the conclusion that there is enough ethylene in the gas to account 

 for its toxicity. The exposure of potted plants to rather low 

 concentrations of gas in a small greenhouse showed that the 

 vegetation is far more resistant than the buds or flowers, and 

 that the very young buds and those showing color are far more 

 injured than the buds of medium age. 



Our experiments in which the individual buds were enclosed 

 and exposed to illuminating gas began with liter flasks in which 

 as much as 25cc. of gas was used. The time of exposure was 

 usually three days, starting when the petals were just beginning 

 to show. A gradual reduction of the concentration by reducing 

 the amount of gas used and by increasing the size of the enclosure 

 finally located the toxic limit. The highest concentration did 

 no apparent injury to the vegetation; but the effect upon the 

 buds was made apparent by a failure to open, by a discoloration 

 and withering of the petals, and by the projection of the stigmas. 

 When using lcc. of illuminating gas to 20,000 cc, the stigmas 

 still project as shown in Figure 2a. The use of 

 0.5 cc. of illuminating gas did not sufficiently 

 retard the growth of the petals to cause projection 

 of the stigmas, yet the buds never opened farther than shown in 

 Fig. 3, although the petals remained fresh for several days. 

 Very young buds were also exposed to the last concentration 

 of the gas (1 part in 40,000 or 0.0025 per cent.) for a period of 

 three days. The injury was not apparent at first, and the 

 buds remained green for several days, but finally turned brown 

 and withered. 



A series of exposures was also made upon the open flowers. 

 We selected for this work those that had just opened,in order to 

 be sure that any change produced was due to the toxicity of the 



