258 Plant Biology 



Of the immense number of plants more or less important to man, 

 only a few which yield such products and materials as fuels, oils, plant 

 fibers, cork, woods, gums and resins, dyes or coloring materials, foods, 

 beverages, flavoring substances, spices, savory substances, medicines and 

 poisons will be considered. 



Fuels. — A fuel may be defined as a plant substance which has stored 

 the energy of the sun during its life and releases it upon burning or 

 combustion. 



Wood (when perfectly dry) consists of nearly 99 per cent combustible 

 materials and 1 per cent inorganic matter, which remains as ash when 

 burned. An increase in the water content of wood reduces its fuel 

 value by taking the place of combustible material and also by using 

 some of the heat produced to evaporate the water. Wood is the most 

 widely used of all plant fuels. 



Peat is a deposit of more or less carbonized plant substances which 

 have accumulated and decomposed under pressure in wet marshes and 

 bogs. Peat is a useful and efficient fuel in regions where coal is scarce. 

 When buried a long time, the peat may resemble a soft brown coal. 



Coal is the remains of ancient and extinct plants so changed under 

 pressure that the resulting material is much harder and more completely 

 reduced to carbon than peat. Coal has much more heating power than 

 peat or wood. 



Charcoal, which is nearly pure carbon, is made by burning wood in a 

 minimum of oxygen, usually by burning piles of wood in mounds cov- 

 ered with earth. Charcoal is mixed with sulfur and saltpeter to make 

 gunpowder. It is also used in making charcoal drawings and for a great 

 variety of other purposes. 



Coke, which is nearly pure carbon, is made by burning coal in a 

 minimum of oxygen, usually by covering piles of burning coal, or in 

 special coke ovens. Coke produces very little smoke. 



Artificial gas is made by subjecting wood or coal to a high tempera- 

 ture and collecting and purifying the gases evolved. This gas is used in 

 communities where natural gas is not available. 



Natural gas is the product of plant decomposition in which there is 

 produced a gas, the important constituent of which is methane (CH4). 

 It is used to a great extent for heating and cooking purposes, being 

 transported many miles from "gas wells" to the consumer. This gas is 

 usually formed under great pressure and rapidly and forcefully comes 

 to the surface when a gas "pocket" is tapped by drilling. 



