76 OF WOOD IN GENERAL. 



against dry rot, and exposure to really dry air is fatal to the 

 fungus. If only the ends of properly seasoned beams which are 

 inserted in brick walls are previously creosoted, it will prove a 

 most effective protection. 



Burrs. Another class of malformations of considerable interest 

 to the timber-merchant are the gnarled and warty excrescences 

 known as burrs or knaiters. These are sometimes due to some 

 mechanical injury to the cortex, at other times apparently to the 

 sudden exposure of a previously shaded stem to the light, as by 

 the felling of a neighbouring tree. They consist of a number of 

 adventitious buds, capable of growing in thickness and putting on 

 wood, but insufficiently nourished to grow in length. In course 

 of years they may grow several feet across, their wood being very 

 irregular, and, owing to its slowness of formation, very dense. 

 The cross-sections of these bud-axes, as in the " bird's-eye " variety 

 of the Hard Maple (Acer barbdtum), the Elm, the Yew, the Walnut, 

 and other species, furnish beautiful veneers. 



Injurious animals. Brief mention must be made here of 

 three classes of enemies to both living and converted timbers, viz. 

 the ship-worms or Teredos, the termites (erroneously known as 

 "white ants"), and various insect-larvae known generally as 

 "worms." Teredo navdlis, the ship-worm, and its allies, are 

 bivalve mollusks, which bore into most kinds of timber when 

 immersed in sea-water, some very dense species, and especially 

 those with pungent resinous secretions, being proof against them. 

 On the other hand, creosoting is by no means always sufficient to 

 keep off their attacks. Shipworms occur in all seas : they gene- 

 rally bore with the grain, lining their burrows with a layer of 

 calcareous matter, and carefully avoiding one another's burrows. 

 They will sometimes completely riddle timber within four or five 

 years. In Australia they are known as "cobra." 



The termites belong to the Neuroptera, an entirely distinct 

 Order of the insect class from that to which the true ants belong. 

 They occur in a great variety of species throughout the Tropics 

 but especially in South America, living in societies of prodigious 

 numbers, and, no doubt, fulfilling a useful function in the economy 



