THE FEBNCH SYSTEM OF PRUNING. 281 



been made for a long time to discover some method 

 of covering the wounds inflicted on trees, either 

 accidentally or by the hands of man. The remedy 

 usually recommended from time immemorial is the 

 ointment of St Fiacre, a mixture of loam and cow- 

 dung. Various preparations too, used in grafting, and 

 having resin, wax, and grease as their basis, have at 

 different times been very generally recommended for 

 this purpose. These preparations are expensive ; and 

 as they must be applied hot, it is not practicable to 

 use them on a large scale. Their use, too, is attended 

 with serious difficulties. As the new growth of wood 

 spreads over the wound, these thick coatings are 

 either broken or pushed aside bodily, according to the 

 power of resistance of the material used ; and the 

 wood is again exposed, and a safe retreat for injurious 

 insects prepared. 



" One coat of coal-tar is sufficient for wounds of 

 ordinary size ; but when they are exceptionally large, 

 a second coat may, after a few years, be well applied. 

 In warm countries, like the south of France, the great 

 heat of summer renders coal-tar so liquid that it is 

 often impossible to properly treat wounds made at 

 that season. In such cases another, coat should be 

 applied during the following winter. 



" Effects of Goal-tar on the Elm. — The effect of coal- 

 tar on the elm is not always as satisfactory as upon 

 other forest-trees, ' such as the oak, ash, sycamore, 

 birch, maple, &c. The application of a coat of coal- 

 tar on all of these gives at once to the wound a hard 

 firm surface ; on the elm, however, it does not always 

 adhere firmly, owing to the formation on the surface 

 of the wound of the water-blisters common to this 

 tree. In such cases the coal-tar which does not ad- 



