176 



GROWTH OF PLANTS 



have dissolved in the soil and been absorbed by the plant in sufficient 

 amounts to induce these changes with such slow flow. These statements 

 are in accord with the findings of the experiments of Harvey and Rose, 

 where they flowed illuminating gas very slowly through the soil. With a 

 very slow flow of gas, it is also probable that HCN would be disposed of by 

 microorganisms in the soil, so it would not accumulate in tissue-killing con- 

 centrations. It is evident from what has just been said that two different 



Figure 65. Effect on the tomato of residues left in soil by ethylene and by illumi- 

 nating gas. Left: control. Center: 10 cubic feet of ethylene. Right: collapse of roots and 

 lower part of stem in soil caused by the residues from three cubic feet of illuminating 

 gas. Photographed six days after seedlings were planted in the soil. 



types of injury may appear in trees and shrubs along leaking gas lines: if the 

 leak is slight, ethylene responses will appear; if the leak is large, the root 

 systems and plants will be killed and none of the growth responses will 

 occur. These investigators ^^ found that the carbon monoxide of the 

 Yonkers gas, although it constituted 13 per cent of the gas, was not a factor 

 in the injury of plants in the soil outside. 



Toxicity of Gas Residues in the Soil 



A comparison of Fig. 64A and B shows that the tomato plant is injured 

 to about the same degree whether it is in the soil while the illuminating 

 gas flows through the soil or is set in the soil immediately after gassing. 



