148 Toxic Action of Traces of Coal Gas vj^on Plants 



In the carnation the flower bud fails to open, the petals are dis- 

 coloured and withered, leaving the stigmas protruding. In the leaves 

 of Ricinus and in other leafy shoots, epinastic movements are the first 

 indications of injury. Harvey's experiments upon Ricinus show that in 

 this plant leaf-fall occurs with relatively very low concentrations of the 

 gas around the leafy shoot. In other experiments where leaf discolora- 

 tion or leaf-fall has been reported it is in all probability a secondary 

 effect following upon damage done to the root system by the gas. 



Many statements draw attention to the effect of the gas upon super- 

 ficial corky tissue; Stone (17) reported proliferation of tissue at the 

 lenticels of willow slips growing in water charged with the gas, Doubt (3) 

 reports the development of soft spongy tissue in the lenticels of Hibiscus 

 and Sambucus, and upon the leaf scars of Lycopersicum, also the 

 appearance of deep longitudinal cracks in the bark of many woody 

 plants, apple, pear, ash, etc. Harvey and Rose (5) also noticed prolifera- 

 tion at the lenticels of roots when gas was slowly passed through the soil, 

 whilst Richter{i5) had noted the same effect produced by tobacco smoke. 



Toxic Constituents of the Gas. 



Nelbujow(9) was the first to show experimentally that the effect upon 

 etiolated seedlings might be traced to unsaturated hydrocarbons which 

 could be removed by passing the gas over red hot copper oxide. He 

 also showed that ethylene in particular, if present alone at a very high 

 dilution indeed, was capable of producing similar effects upon plants. 

 The exhaustive experiments of Crocker and his colleagues (2, 3, 4, 5, 6) 

 have placed this result beyond all doubt, and they show also that 

 other possible poisonous constituents such as prussic acid, carbon 

 monoxide, sulphur dioxide, etc. if present in the atmosphere in con- 

 centrations equivalent to that provided by the toxic amount of 

 illuminating gas or tobacco smoke, are completely without action upon 

 the plant. Wehmer(i8, 19, 20), who has recently attributed the toxic 

 action of coal gas, first of all to benzol and its homologues and sulphur 

 compounds, and then later (2i, 22) to hydrocyanic acid gas, appears to 

 have been unaware of the earlier work of Crocker and his colleagues. 

 In any case his experiments are not strictly comparable as he works 

 with very high concentration of coal gas, in many experiments 100 

 per cent.; furthermore, he does not obtain toxic effects when these 

 constituents are introduced into air at concentrations equivalent to 

 those in which they occur in toxic concentrations of coal gas. The 

 proportion of unsaturated hydrocarbons present in the illuminating gas 



