Arthur G. Ruston 395 



the case of a large variety of leaves, and the deposit thus found can 

 easily be correlated with the known amount of smoke pollution in the 

 district in which they have been grown. 



The figures given are those found in the case of laurel leaves grown 

 in the districts indicated. 



A microscopic examination of the leaf will reveal the fact that when 

 the plants have been grown in a smoke-polluted atmosphere more or 

 less of the stomatal openings will be choked with a tarry deposit. This 

 will be particularly noticeable in the case of evergreens and most 

 especially in the case of the conifers (Fig. 6, PI. XXV). The leaves from a 

 juniper grown at Garforth, six miles from Leeds, but well in the drift 

 of the smoke from Hunslet, were examined by Mr Hector, Lecturer in 

 Agricultural Botany, and he reported that 75 per cent, of the stomatal 

 openings were more or less choked in this way. 



We may notice in a general way that flowers grown in a smoke- 

 polluted atmosphere lose their brightness of tint; but it is possible by 

 means of a tintometer to get an accurate measure of their colour. I am 

 indebted to Mr Frank of the Dyeing Department of the University of 

 Leeds for the trouble he has taken in analysing by means of Lovibond's 

 tintometer the colours of a large number of flowers. These flowers have 

 been grown in each case from plants propagated at the Stapleton 

 Gardens, Pontefract, from the same parent plant, by Mr Dobson, an 

 old student of the Agricultural Department of the Leeds University, 

 whose assistance in this and many other respects has been invaluable. 



Three sets of readings are given. 



Blood-red Wallflowers, June 13th, 191-1. 



Direct tintometer readings 



Annual Total colour 



District deposit Red Blue Yellow units 



Weetwood Lane 42 36-5 70 4 47-5 



University 114 22-5 2-5 9 340 



Hunslet 539 13-0 11 9 231 



26—2 



