702 PROTECTION AGAINST DISEASES. 



and oak as suffering most of all broadleaved species from 

 acid fumes and even places them above the larch in this 

 respect. 



Borggreve at Miinden drew up a similar table to that of 

 Schroder, in the following order : 



1. Silver-fir, spruce, Scots pine. 



2. Beech, lime, poplar, alder, maples, and ash. 



3. Hornbeam, aspen. 



4. Oak (least susceptible). 



According to Hess's* own experiments elms (Ulmus mon- 

 tana and campestris) must be reckoned among resisting species. 



The above grouping cannot always be relied on, as there 

 are too many modifying factors in particular cases. London, 

 with its constant coal-smoke and numerous factories and 

 frequent dense sulphurous fogs, should give better practical 

 results as to the comparative powers of resistance of trees 

 than any merely artificial laboratory experiments. 



There are fine large flourishing plane-trees (Platanus 

 orientalis y \ L.) in Cheapside and on Ludgate Hill, which are 

 entirely surrounded by tall buildings, and the plane is 

 growing well on the Thames Embankment and in many parts 

 of London. The plane-tree sheds large flakes of its bark 

 annually, and its buds are sheltered by its sheathing petioles ; 

 these facts probably contribute to its immunity. 



The following account of the trees and shrubs which flourish 

 in the Botanic Garden in Regent's Park, London, has been 

 kindly supplied by J. W. Sowerby. 



" Of the plane there are many very large trees. Maples 

 of several species and varieties. Horse-chestnuts flower 

 and fruit as well as in the country. Poplars of many 

 species.! Elms, of which a belt surrounds the gardens, 

 and one old elm which was on the ground in 1838 is still 

 healthy. 



* " Fretl. Blttr.," 1874, p. 31. 



f Masters and Webster recommend for town planting P. orientalis acerifolia, 

 which has less deeply divided leaves than the normal plant, and may be dis- 

 tinguished from P. occidentalis, L., by the many fruit-balls attached to its 

 peduncles. 



I Pojnilii* canademis, Desf., has a reputation in the Black Country for immunity 

 from the effects of fumes. P. balmmifera, L., is growing well in St. James' Park. 



