ON THE EFFECTS OF URBAN FOG UPON CULTIVATED PLANTS. 35 



clodendron, Begonia (Winter Gem), and Justicia carnca may be 

 quoted. I confess that I was astonished to find how perfectly 

 these flowers opened under these conditions. It should be 

 added that the whole plant was not darkened, but only the 

 inflorescence or flower-bud. Had the supply of food-material 

 — except in those cases in which flowers are formed at the 

 expense of considerable reserves of nutritive matter — been 

 checked by previous darkening of the foliage, the results might 

 have been very different. 



Action of Fog. 



Speaking generally, flowers and flower-buds are the first 

 portions of a plant to exhibit suffering. In distant suburban 

 localities the detrimental action of fog upon vegetation is, in 

 very many cases, confined to floral injury. The same result is 

 noticed after a town fog of only moderate severity. A fog last- 

 ing six or seven hours frequently leaves its traces upon the more 

 delicate classes of flowers. Its effects only differ in degree from 

 the more serious injuries. 



The injuries to expanded flowers include a loss of substance in 

 the corolla, accompanied by an abnormal translucency ; whilst fre- 

 quently there is a slight browning or blackening of the apices and 

 margins of the organs. Ultimately the affected parts shrivel and 

 become desiccated. Many white flowers become slightly yellowed 

 and transculent, whilst others develop blotches. Others, again, 

 appear to be uninjured. Flowers possessing a delicate pink or 

 blue colour often lose this colour entirely or in part. In this con- 

 nection may be instanced pink Calanthes, pink and mauve 

 Acanthacece, Vanda ccerulea, Bouvardia, and the like. Finally, 

 there are flowers which readily disarticulate, sometimes showing 

 one of the above forms of injury (Phalcenopsis) or, occasionally, 

 intact (Pleroma macrantha). In general, however, where no 

 specific or noticeable injury is caused, flowers wither sooner 

 than would otherwise be the case if any portion of their period of 

 expansion coincides with a spell of fog. It must be understood 

 that when I speak hereafter of any flower as being uninjured, 

 I mean that no immediate or local lesion is produced. 



Injuries to flower -buds are most frequent at the stage im- 

 mediately preceding the opening of the flower. They show 

 discoloration and desiccation much in the same manner as 



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