9] VITAL IMPORTANCE TO MANKIND 271 



Upholstery, stiffening, packaging, and caulking, the outstanding 

 example being kapok {see p. 235) and its various substitutes, which 

 include the silky hairs on the seeds of the familiar Milkweeds. 

 There is also Spanish-moss, an excellent substitute for horsehair. 

 (7) Natural fabrics, etc., consisting of tough interlacing fibres that 

 can be extracted from bark in layers or sheets and used as a sub- 

 stitute for cloth. Examples include the Polynesian and Oriental 

 tapa cloth and the Jamaican lace-bark, as well as such fibrous pro- 

 ducts as the so-called vegetable sponges or luffas which are used 

 for making hats, for scouring, for filtering, and as substitutes for 

 bath sponges and body scrapers. 



Fuels (including Fossil, etc.) 



Fuel, as a source particularly of heat, light, and power, is one of 

 the greatest necessities of human life, and in general consists of 

 plants or plant products whether modern or belonging to earlier 

 epochs. A few of the main groups of plant materials that are widely 

 used as fuels may be outlined : (i) wood, probably still used more 

 for fuel than for any other purpose, certain hardwoods being in 

 general better than other types, but almost all woods making useful 

 fuels when dry ; (2) vegetable oils, used principally in this connection 

 for illumination and for powering Diesel engines ; (3) peat, con- 

 sisting of compacted deposits of partially decomposed vegetable 

 matter, which is widely used for heating and cooking in northern 

 lands especiallv where wood is scarce ; (4) manure, which is the 

 almost universal fuel of hundreds of millions of people in southern 

 Asia ; (5) coal, the compressed and fossilized remains of plants that 

 lived in much earlier geological epochs and are now largely decom- 

 posed and converted into carbon, being a valuable and wddely used 

 source of fuel and power and also of gases which are employed 

 particularly for heating and illuminating ; (6) coke, w^hich is left 

 when coal-gas is driven off from coal, and is nearly pure carbon, 

 forming an excellent fuel which burns without appreciable smoke 

 or flame ; (7) charcoal, which bears a similar relationship to wood, 

 and is the chief domestic fuel in many tropical countries ; (8) saw- 

 dust, etc., used principally in the form of briquettes ; and (9) 

 petroleum, \yhose familiar products of distillation include the all- 

 important gasoline (petrol) as a source of power, and paraffin and 

 kerosene as sources particularly of heat and light. Although no 

 trace of plant structure remains in petroleum, it is generally supposed 



