26 TECHNICAL PROPERTIES OV WOOD. 



(iv). Fairly durahle.—Anogeissus spp., tun, mango, Terminalia 

 belerica. 



(v). Quick to decay. — Odina Wodier, Adina cordifolia, semal, 

 Butea frondosa, Boswellia serrata. 



(vi). Very quick to decay. — Cochlospermum Gossypium, Mo- 

 ringa spp., Dalbergia paniculata, Sterculia spp. 



Insects and other animals. — Except in the special case of wood 

 used in contact with sea-water, the animals we have to fear are 

 insects. For our purpose we may divide timher-destroying insects 

 into three classes, viz., (1), those which can enter only fresh-felled 

 wood as larvse, (2), those which attack wood already in use, but 

 only as larvse, and (3), those whose full grown individuals attack 

 the wood and commit all the ravages. 



In the first class of insects the mother deposits her eggs on, or 

 in, the hark of fresh-felled wood, and the larvse, after being hatch- 

 ed, eat their way into and inside the wood. According to the 

 size and number of the larvas, broad " galleries " are formed, or 

 the wood becomes literally riddled with small holes (worm-eaten). 

 To prevent the ravages of such insects, it is suificient to bark the 

 trees in time, thus getting rid of eggs already laid, and either 

 preventing new ones from being laid, or, owing to the drying up 

 and consequent hardening of the surface of the exposed wood, 

 preventing the weak, freshly hatched larvse from gnawing their 

 way to the moist and therefore softer tissues inside. The ease of 

 the various species of bamboos presents an anomaly in that they 

 have no bark which can be removed ; but submergence in water 

 for a few days 'or, better still, floating washes off the eggs. Fel- 

 ling bamboos during the dark half of the lunar month also preserves 

 them from the attacks of insects. Prolonged floating or submer- 

 gence in water also preserves all other kinds of wood by drown- 

 ing the larvse. Where the use of such substances is cheap enough 

 and not objectionable, the wood may be impregnated with insect 

 poisons, such as metallic salts, creosote, kerosine oil, &c. Steaming 

 will also of course kill all the eggs and lai-vse. The wood of 

 broad-leaved species is more liable to the attacks of insects than 

 conifers, which are partly protected by the aroma of the turpen- 

 tine. The sapwood, on account of its softer texture and the 

 reserve starch and other food it contains, is very much more visited 

 by insects than the heartwood. 



The second class of insects include the genera Ptinus and Anobi- 

 wm (death watch), which attack wood used in dwellings, especially 

 in dark places in the roof. The larvse eat their way through the 

 wood in every direction, reducing it to a spongy brittle mass that 



