TOWN SMOKE AND PLANT GROWTH. 463 



Table 11. — Impurities in Leeds Rain. (Pounds falling on each acre per annum.) 



No. 



CoUectiug Station 



Nature of Locality 



Total 

 Suspended 

 Matter 



Tar 



Sulphur 



Chlorine 



Nitrogen 



Free Acid 

 expressed 

 as 



Sulphuric 

 Acid 









lb. 



10. 



lb. 



lb. 



lb. 



ID. 



i 



Jjeeds s orge 



Industrial 



1886 



1 1 n 



169 



164 



17-7 



do 



2 



Hunslet 



Residential, near industrial 



1565 



oy 



215 



198 



18-4 



yu 



3 



rJeeston xiiu 



1163 





336 



101 



18-4 







Philosophical 



















Hall 



Commercial centre 



849 



78 



197 



75 



16-9 



45 



5 



Headingley 



Residential 



659 



43 



158 



41 



130 



11 



6 



Armley 



Residential, near industrial 



593 



34 



156 



108 



14-1 



29 



7 



Woodhouse 



















Moor 



J5 11 11 



399 



32 



134 



51 



10-8 



26 



8 



Kirkstall 



Residential 



352 



28 



147 



57 



10-2 



8 



9 



Weetwood 



Residential (outskirts of city) 



147 



26 



98 



34 



11-5 



11 



10 



Roundhay 



11 11 11 



90 



14 



73 



38 



7-8 



0 



The results indicated a striking degree of pollution in all parts of 

 the city, even the more remote residential suburbs receiving very 

 appreciable quantities of air-borne impurities. 



Influence of Atmospheric Impurities upon Plant Growth. 



The attempt was next made to study more closely those aspects of 

 smoke-pollution which might be expected to affect prejudicially the 

 growth of plants. 



Such a detrimental influence may be exercised in a variety of ways. 

 Thus the suspended insoluble matters (visible smoke) may impede 

 growth : 



(a) By reducing the amount of light that reaches the leaves ; 



(b) By blocking up some O'f the stomatal openings of the leaves 



through which the carbonaceous food of the plant is taken 

 up; ^ 



(c) By the poisonous influence of certain consiituents of the 



suspended matters, e.g. sulphides. This influence may be 

 exercised directly upon the plant or indirectly through the 

 soil. 



Some of the soluble impurities may also have a detrimental influence. 

 This will certainly be the case with the lower sulphur compounds 

 ! (sulphuretted hydrogen, &c.) and free acids. 



Influence of Smoke upon Intensity of Light. 



Comparison of the records of sunshine recorders in the heart and 

 on the northern outskirts of Leeds showed that in the city the duration 

 of bright sunshine was curtailed by fully 17 per cent. But the sun- 

 I shine recorder takes no account of light whose intensity falls below a 

 I certain arbitrarily chosen standard of brightness, but which is neverthe- 

 I less of use tO' plants. We attempted, therefore, to compare the total 

 daylight in different parts of Leeds by means of a more refined method 

 j of measurement. This consisted in exposing at six of the centres equal 



i 

 i 



