[Chap. XLI NON-GREEN PLANTS 511 



between saprophytes and parasites, and also between these two groups 

 and the autophytes. Many terms have been proposed to designate these 

 intergradations.^ Some of this diversity is related to ( 1 ) the kinds of 

 substances the organism can digest and utilize as food, (2) the method 

 of securing food, and (3) the kind of substance oxidized during 

 respiration. 



In the cells of all animals, of all green plants, and of most non-green 

 plants also, respiration involves the oxidation of reduced carbon atoms 

 in sugar, or in organic compounds derived from sugar. When this oxi- 

 dation is complete, one of the end products is carbon dioxide. A few 

 groups of bacteria, however, are unique in that they oxidize reduced 

 nitrogen, reduced sulfur, or reduced iron. Consequently nitrates, sulfates, 

 and oxidized iron in the soil are among the end products of respiration 

 of these bacteria. The oxidized compounds are essential to green plants, 

 which are therefore partly dependent upon the activities of these bac- 

 teria. The bacteria in turn are partly dependent upon the activities of 

 green plants for reduced nitrogen, and upon both green plants and other 

 kinds of bacteria for reduced sulfur and iron. 



These special groups of bacteria are unique in one other way. Al- 

 though they are non-green and are underground, they synthesize sugar 

 from carbon dioxide and water. The energy necessary for this synthesis 

 is obtained from the oxidation of reduced nitrogen, sulfur, and iron. 

 They are as truly autophvtes as the green plants. The synthesis of sugar 

 in these bacteria in the absence of light is often referred to as chemosyn- 

 thesis in contrast to photosynthesis. Similarly, certain bacteria may oxi- 

 dize reduced manganese and synthesize sugar. 



The green and some purple bacteria ( Plate 3 ) contain pigments simi- 

 lar to chlorophyll; and when they are exposed to light, photosynthesis 

 occurs within them. 



Autophytes. All plants, whether green or non-green, in which sugar is 

 synthesized from carbon dioxide and water are called autophytes in con- 

 trast to parasites and saprophytes. Perhaps the term should be limited to 

 those in which the synthesis of amino acids and proteins also occurs. 

 Most autophytes, however, are not independent plants. They could not 

 continue to live in a world devoid of all non-green plants. The non-green 

 plants are dependent upon certain reduced compounds made in the 



^ J. M. Coulter, C. R. Barnes, and H. C. Cowles, A Textbook of Botany, American 

 Book Company, 1931, Vol. 3. 



