INJURIES TO PLANTS BY LONDON FOG, AND ENGINE SMOKE. 313 



This turns brown, and the action then passes on to the subjacent tissues 

 until it has worked its way through the leaf. 



It often happens that disarticulation takes place with great rapidity, 

 even while the leaves are green. The fog enters the lacunae of the leaf 

 through the stomata. In other cases varying degrees of yellowing or 

 browning precede disarticulation. 



When this is the case it closely resembles autumnal fall of the leaf, 

 in that all useful materials, as starch, oil, &c., are removed before the leaf 

 falls. This, too, is brought about by the usual "absciss" layers, but 

 formed abnormally and very rapidly. It is thought that some ferment 

 may be produced which may assist in the process by dissolving the tissues, 

 so as to account for the rapid fall. 



The disarticulation can take place in forty-eight hours after the 

 commencement of the fog. In the Palm-house many bushels of green 

 leaves were gathered up almost every morning during a persistence of 

 London fog. 



Speaking generally, the flowers and flower- buds are the first to suffer. 

 The injury may, in fact, be confined to these at distant localities. Thus, 

 near Richmond, a Camellia lost 100 buds in one night, but was not other- 

 wise injured. If the flowers be half expanded, discoloration and desicca- 

 tion occur, as this is the most critical period. If they be fully expanded, 

 flowers will sometimes escape injury. Prof. Oliver remarks of Rhodo- 

 dendron jasminiflorum that the flowers were uninjured as long as 

 the inflorescence remained wrapped in bud-scales. But when the buds 

 attempted to open during the prevalence of a fog they were caught. The 

 buds pushed the scales aside, but rarely succeeded in freeing themselves 

 from them. 



With regard to the eflects of London fog at Kew, it is said that Ferns 

 scarcely s-uffer at all. This is remarkable, because in the case mentioned 

 above, where Ferns were largely grown for market, they became unsale- 

 able in consequence of the eflects of the smoke from adjacent railway 

 eni?ines. 



Lastly, the Curator of the Botanic Gardens, Regent's Park, has made 

 the following observations upon the injury sustained there : — 



" The Botanic Gardens aftbrd a good example of the increasing 

 damage due to this cause. As is well known, many plants, such as the 

 Conifers, will not live in the open air within the Metropolis ; even in the 

 greenhouses it is the same ; — the purer air is counterbalanced by the loss 

 of light arising from soot-covered glass. The Kitchen Garden of the 

 Gardening School stands upon what, thirty years ago, was a Rose Garden 

 where most of the principal varieties of this lovely flower flourished in 

 company with great clumps of white Lilies, Phloxes, Carnations, and 

 drooping masses of purple Clematis. At that time it was one of the most 

 beautiful features of the Gardens, but as the growth of London became 

 more rapid,, and the air more deteriorated, first one plant sickened, and 

 then another, until only the name was left, and the ground had to be 

 turned to other uses. A few of the old roots which showed anv siijns of 

 life were removed to the purer atmosphere of Ealing and recovered : these 

 when last seen were flowering well, and doubtless are doing so now, since 

 there is hardly any limit to the life of a Rose." 



D 



