ON THE EFFECTS OF URBAN FOG UPON CULTIVATED PLANTS. 147 



in London and its suburbs, on precisely the same lines as those 

 being employed in Manchester — the two inquiries, so far as the 

 chemical investigation of fog is concerned, running pari passu. 

 Dr. Bailey, with whom I have been in constant intercourse, is 

 willing to co-operate in this undertaking, the experiments and 

 analyses in question being made under his direction and control. 

 This joint scheme has, I think, the additional recommendation 

 of being likely to produce total results of greater value, and at 

 a less expenditure of energy, than if the investigations at Man- 

 chester and London be conducted independently. Dr. Bailey 

 and his colleagues have just issued a preliminary report on the 

 atmosphere of Manchester. I would call special attention to 

 this, as indicating the method and scope of the undertaking. 

 The report in question is now appearing, in extenso, in the 

 Northern Gardener. 



V. Physiological and Microscopic Work. — The opportunity 

 has been taken to have careful drawings prepared, exhibiting 

 typical cases of damage attributable to fog. I have now a con- 

 siderable collection of examples from the Koyal Gardens, Kew, 

 and elsewhere. 



Large supplies of injured plant organs have been forthcoming 

 and have been submitted to chemical analysis. These include 

 the leaves of soft- and hard- wooded plants and of Orchids ; also 

 the leaves of Gattleyas and Vendrobiums } and the flowers of 

 Cattleya Triance. The results of these analyses will be valuable 

 for publication when similar analyses of the uninjured parts have 

 been obtained. Incidentally, the presence of quantities of iron 

 salts in the ash may be noted. I cannot at present say what 

 may be the physiological bearing of this result. It is possible 

 that a finely divided film of iron oxide on the surfaces of the 

 leaves might promote injurious action in the subjacent tissues. 

 The chief damage I attribute to the sulphurous acid, quantities 

 of which are actually absorbed by the foliage. 



The histological characters of injured tissues, as exhibited by 

 the microscope, have been carefully studied, and drawings and 

 notes made. Many of the facts thus obtained are still obscure, 

 and require experimental elucidation. In the case especially of 

 Orchid flowers the distribution of the stomates would seem to 

 have a definite bearing on the distribution of the fog-injuries. 

 In both Phalcenopsis Schilleriana and Cattleya Triance, for 



