Arthur G. Ruston 399 



mind. The leaves must be taken from the same variety of trees or shrubs, 

 for different types of leaves will absorb sulphur dioxide at different 

 rates and hence possess different proportions of S0 3 . They must also 

 be collected at the same time for the sulphur content of leaves will 

 increase with age. The total sulphur content expressed as S0 3 of syca- 

 more leaves grown in Meanwood and analysed by Steuart was 0-48 per 

 cent, in May and 0-75 in August. 



The sulphur present in the plant will be partly protein and partly 

 non-protein; and leaves grown in a smoke-infested area will not only 

 contain a large amount of sulphur; but that sulphur will be present 

 principally in non-protein forms, mainly sulphates. The following 

 analyses of elder leaves collected in June, 1913, at the stations men- 

 tioned illustrate this point. 



Percentage of S0 3 



Yearly deposit in dry matter Ratio 



of S0 3 in tons , A ^ , A , 



Station per sq. mile Protein Non-protein Total Protein Non-protein 



Sutton about 8 -21 -07 -28 300 



WeetwoodLane 28 -20 -13 -33 154 



Woodhouse Moor 38 -19 -18 -37 105 



Hunslet 96 -11 -48 -59 23 



100 

 100 

 100 

 100 



In the autumn of 1919 the Department of Agriculture of this Uni- 

 versity was asked to investigate a bad case of smoke damage to a 

 growing crop of four acres of potatoes. My estimate of the cost of 

 growing and harvesting the crop, drawn up from the details of cultiva- 

 tion supplied by the owner was £98. 18s. In return for this outlay of 

 nearly £100, two tons of marketable ware were lifted and sold for 

 £18. 18s.; and approximately a ton and a half of small potatoes were 

 fed to the pigs. This would mean that the actual loss in out-of-pocket 

 expenses incurred by the grower could not possibly be less than £70 

 and most probably would be nearer £80. The haulms of the potatoes all 

 showed marked signs of smoke damage, even to the eye. A chemical 

 examination of these showed them to possess an abnormally high sulphur 

 content, and a very low ratio of protein to non-protein sulphur. The 

 total percentage of S0 3 present in the dry matter of the leaves Vas as 

 high as 0-72 per cent., of which only 0-21 per cent, represented protein 

 sulphur, and 0-51 per cent, represented non-protein sulphur. 



A chemical analysis of plants grown in smoke-infested areas will also 

 show that they contain proportions of arsenic increasing with the 

 amount of the smoke pollution. 



A Bacteriological examination of soils in smoke-polluted districts will 



