CHAPTER XXXIV 

 PLANT LIFE. CELLULOSE, STARCH AND SUGAR 



PLANTS and animals are similar in composition. They contain 

 much the same elements, and these are present in the form of 

 similar compounds. They differ sharply, however, hi the foods 

 they use in constructing these compounds. Plants use simple, 

 inorganic materials; animals absolutely require complex, organic 

 substances as food. The main chemical processes, therefore, are 

 very different in the two groups, 



How the Plant Feeds. The walls of the cells which form the 

 frame-work of a plant are made of cellulose (CeHioOs)?. In the 

 cells, especially hi certain parts of the plant, granules of starch 

 (CeHioC^)* are found. These complex substances differ in prop- 

 erties, although they have the same composition. The plant 

 ) contains sugars, such as cane-sugar or sucrose, 



in variable amounts, and also esters (vegetable oils, p. 432) and 

 alkaloids (vegetable bases, p. 479) in much smaller quantities. 

 The plant cells also contain still more complex substances, known 

 as proteins. Qlute^_ihe sticky portion of wheajiJlQur (p. 5), 13. 

 a^typrcahprotein. These proteins are the chief components of 

 the protoplasm, a semi-liquid substance lining each active plant- 

 cell, and the real seat of life of the plant. Now all these substances 

 contain carbon, hydrogen, and oxygen, and plant food must 

 furnish these elements, which constitute over 95 per cent, on the 

 average, of all plants. Hence, in addition to large quantities of 

 water ascending from the soil through the roots and stem, and 

 sufficient amounts of compounds of nitrogen, potassium, phos- 

 phorus, and other elements, all plants require an abundant supply 

 of carbon in absorbable form. This carbon is practically all 



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