9] VITAL IMPORTANCE TO MANKIND 269 



Sugar, as we have already seen, is obtained principally from the 

 Sugar Cane and the Sugar Beet, and though primarily used as food 

 it has also become an extremely important industrial chemical, with 

 thousands of different derivatives. About 35,000,000 tons are pro- 

 duced annually. When speaking of sugar we normally mean sucrose, 

 which is by far the most important and the one usually stored, 

 though other sugars have their places and uses. Further important 

 sources of sucrose are Maize, Sugar Maple, Sorghum, certain 

 Palms, and honey. 



Starches constitute the chief type of food-reserve for most green 

 plants, being stored in the cells in the form of minute grains. 

 Starches are chemically complex but, being easily convertible into 

 sugars, are vastly important as human foods, the chief sources being 

 potatoes, various cereals, arrowroot, cassava, and sago. They are 

 also widely used in industry, for example in laundry and textile 

 work, in sizing, and as sources of glucose, dextrin, industrial alcohol, 

 and explosives. 



Still more complex is cellulose, the chief constituent of the cell- 

 walls of most plants, which yields numerous textile fibres both 

 natural and artificial. The chief sources nowadays are cotton, which 

 is almost pure cellulose, and wood, which by chemical and mechanical 

 treatment is made to yield pure cellulose. This may be made into 

 fibres or plastics, or transformed into wood sugar, which in turn 

 may be made to nourish Yeast or yield alcohol and thus become 

 available for food or industrial use. In addition there is hemi- 

 cellulose, which forms the so-called ' vegetable ivory ' — obtained 

 from certain tropical Palms and useful as a substitute for ivory in 

 the manufacture of buttons and other small, hard objects. 



While paper can be made from most fibrous materials, the chief 

 commercial sources are wood fibres, cotton, and linen. The last 

 two, formerly the main source of paper, still yield the finest grades, 

 but wood fibres nowadays make up the vast bulk. They are 

 obtained from a wide range of trees of which various Spruces, 

 Pines, Hemlocks, and Poplars are among the most important, while 

 sawmill waste is increasingly used. Other raw materials for paper- 

 making include papyrus, esparto, straw, mulberry, and various textile 

 fibres. By special processes the wood or other raw material is 

 pulped, after which a series of operations, including the addition 

 of rosin or other ' sizing ' of plant origin, lead to its manufacture 

 into one or another of the almost innumerable types and grades of 

 paper. The coarser materials are often made into cardboard. 



