WOOD. 349 



and gluten collect in the seed j while sugar and gum 

 exist principally in the sap and fruit, or exude from 

 the bark. 



WOOD. 

 Mention dif- S77 ' W ODY FIBRE. Woody fibre, of 



ferent forms which the fibrous threads of cotton or flax 



of ivoody fibre , j /r 



^-its com- ma Y serve as an example, is composed of 

 position. carbon, hydrogen and oxygen. Its mole- 



cule contains twelve atoms of carbon, to ten of hydro- 

 gen and ten of oxygen. It constitutes the solid mass 

 of all vegetable organs, whether hard and firm, like 

 the fibre of the oak ; soft, like the pulp of fruits ; or 

 fibrous, like cotton and flax. In one or the other of 

 its forms it therefore serves us for shelter, clothing and 

 food. It forms in plants the cells in which the vege- 

 table juices are contained, and the veins or pores 

 through which they circulate ; and has thence received 

 its name of cellulose. In wood, these cells are often 

 lined or filled with a substance of similar composition, 

 to which the name of lignin has been given. 



878. CHANGE BY HEAT GAS, CHAR- 

 changed by COAL, ETC. Under the influence of 

 heat? a high temperature, without access 



of air, wood is converted into charcoal, water, 

 gases, wood vinegar, and tar. It is to be observed 

 that this change is the simple result of a re-ar- 

 rangement of the atoms of the wood itself, with- 

 out the help of additional oxygen or other ele- 

 ments. It is a most remarkable instance of va- 



