18 CHEMISTRY OF PLANT LIFE 



first of these is a constructive one which has at least three different 

 phases: namely, a synthesis of complex organic compounds, the 

 translocation of this synthetized material to the centers of growth, 

 and the building up of this food material into tissues or reserve 

 supplies; and the second is a destructive process of respiration 

 whereby carbohydrate material is broken down, potential energy 

 is released, and carbon dioxide is excreted. 



The synthetic processes which take place in plants are of two 

 types; namely, photosynthesis, in which sugars are produced, 

 and another, which has no specific name, whereby proteins are 

 elaborated. The translocation of the synthetized material 

 involves the change of insoluble compounds into soluble ones, 

 effected by the aid of enzymes. For storage purposes, the soluble 

 forms are usually, though not always, condensed again into more 

 complex forms, these latter changes requiring much less energy 

 than do the original syntheses from raw materials. 



The destructive process, respiration, is characteristic of all 

 living 'matter, either plant or animal organisms. It takes place 

 continuously throughout the whole life of a plant. During rapid 

 growth it is overshadowed by the results of the synthetic process, 

 but during the ripening period in which the seed is matured, and 

 during the germination of the seed itself, growth is practically 

 at a standstill and the respiratory, destructive action predominates, 

 so that the plant actually loses weight. 



GROUPS OF ORGANIC COMPOUNDS FOUND IN PLANTS 



As a result of their various synthetic and metabolic activities, 

 a great variety of organic compounds is produced by plants. 

 Certain types of these compounds, such as the carbohydrates and 

 proteins, are necessary to all plants and are elaborated by all 

 species of autotrophic plants. Other types of compounds are 

 produced by many, but not all, species of plants; while still others 

 are found in only a few species. It is fairly easy to classify all 

 of these compounds into a few, well-defined groups, based upon 

 similarity of chemical composition. These groups are known, 

 respectively, as the carbohydrates and their derivatives, the glu- 

 cosides and tannins; the fats and waxes; the essential oils and 

 resins; organic acids and their salts; the proteins; the vegetable 

 bases and alkaloids; and the pigments. A consideration of these 



