OF PLANTS. 319 



so much on the muddy shores of tropical coun- 

 tries, and form a sort of soil like the Ultima Thule 

 of the ancients, neither land nor sea, are a remark- 

 able instance of that, and the maritime pines of 

 the Mediterranean shores are another. Metallic 

 fumes are very hurtful to vegetation, more espe- 

 cially those that contain lead ; and the trees near 

 lead mines are few and sickly. Saline efflo- 

 rescences upon the surface of the ground destroy 

 vegetation; and works where sulphur is burnt into 

 sulphuric acid, and those at which Prussian blue, 

 and various other colouring matters are prepared, 

 are, if possible, more so. 



Now it is evident, whatever substance has an 

 injurious effect upon trees in an advanced stage 

 of their growth, must be much more injurious to 

 them at the very commencement. But the com- 

 mercial advantages of having nurseries for forest 

 trees, as well as other plants, near great towns, 

 are so many, and so much more obvious than the 

 injuries that may thus be done to the trees, that 

 many of them are in very tainted atmospheres. 

 Ground there is high rented, and the plants are 

 in consequence huddled together as closely as 

 possible both in the seed beds, and after they are 

 transplanted. Still with the rich soil and skilful 

 management in such places, the trees rush up 

 quickly and look well, so that they are more 

 " taking to the eye," and so fetch higher prices, 

 than if they were to produce better timber. In- 

 deed those plants, inferior as their timber must 

 be, are actually the most acceptable to the imme- 

 diate planter. Most species of forest trees are so 

 long in coming to maturity, that the grand incen- 

 tive to the planting of them is ornament and not 



