400 



Plant as an Index of Smoke Pollution 



also in many cases supply information which will be of service in deter- 

 mining the amount of that pollution. The acidity of the smoke will 

 deplete the soil of its calcium carbonate and in so doing will modify to 

 a large extent the number and activity of the soil flora. The greater the 

 acidity of the soil the smaller the number of bacteria present in the soil, 

 and the less their activity; the nitrifying organisms being found to be 

 the most susceptible. 



The following table gives the results of bacteriological examination 

 of the soil taken from Garforth and exposed for three years in the 

 districts mentioned. 



These results indicate clearly that the detrimental effect of the 

 smoky atmosphere upon plant growth is partly due to unfavourable 

 changes in the soil— such as the steady depletion of the stock of calcium 

 carbonate, and the inhibition of the activities of the nitrogen-adapting 

 soil flora. 



We may notice that plants grown in a smoke-polluted atmosphere 

 lose their vitality; but it is possible in a large number of ways to get a 

 measure of that loss of vitality and to use the information thus obtained 

 to gauge the amount of smoke pollution in different districts. 



This loss of vitality will be shown in a diminution of the Repro- 

 ductive Powers of the Plant, whether propagated from seed or from 

 cuttings. 



(a) The following table gives the germination capacity of oats grown 

 in 1913 at the stations indicated. 



