BUERS— INJUEIOUS ANIMALS 63 



absence of ventilation) its spawn-threads spread not only in all 

 directions through, the wood, forming greyish-white cords and 

 flat cake-hke masses of felt on its surface, but even over surfaces 

 of damp soil or brickwork, and thus to other previously uninfected 

 timbers. Feeding upon the elements of the wood, getting its nitrogen 

 from cells which retain their protoplasm, such as those of the pith- 

 rays, but its carbonaceous and mineral substances from the walls 

 of the tracheids and other fibrous elements, the fungus destroys 

 the substance of the timber, lessening its weight, and causing it to 

 warp and crack ; until, at length, it crumbles up when dry into a 

 fine brown powder, or, readily absorbing any moisture in its neigh- 

 bourhood, becomes a soft, cheese-Hke mass. At an earHer stage 

 the affected timber appears dark-coloured and dull ; and, long 

 before its total disorganization, it will have lost most of its strength. 

 Imperfectly seasoned timber is most susceptible to dry rot ; the 

 fungus can be spread either by its spawn or by spores,and these latter 

 can be carried even by the clothes or saws of workmen, by currents 

 of air, by rats, mice or insects, and are, of course, only too Hkely 

 to reach sound wood if diseased timber is left about near it ; but 

 on the other hand dry timber kept dry is proof 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 Jcnauers. 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 felhng of a neighbouring tree. They consist of a number of 

 dormant 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 harbdfum), the Elm, the Yew, the Walnut, 

 the Oak, and other species, furnish beautiful veneers. 



Injurious animals* — Brief mention must be made here of three 

 classes of enemies to both Hving 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 moUusks, 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. 



