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THE 



ITURALIST [Vol.LII 



require their food to be ready manufactured for their use, 

 and those which can manufacture their own food (proto- 

 trophic). It is apparent that the primitive organism was 

 I » robably prototrophic. 



The manufacture of food from inorganic materials re- 

 quires the expenditure of energy. We must account, if 

 possible, for the sources of such energy for the proto- 

 trophic forms. Among modem organisms the energy 

 needed is secured always from one of the two sources, 

 light rays or chemical oxidation. While other types of 

 energy are known, apparently plants have not been 

 adapted to their utilization. If light rays were first used 

 as an energy source, the primitive organism was prob- 

 ably provided with some pigment which was of signifi- 

 cance in the absorption of the light and in its conversion 

 into chemical energy. Among modern forms which may 

 have resembled such primitive organism may be cited the 

 simpler types of the blue-green algae and the phototactic 

 sulphur bacteria containing the pigment bacteriopur- 

 purin. If the Chamberlin planetesimal hypothesis of 

 earth origin is accepted, Mich might very possibly have 

 been the primitive types. However, primitive conditions 

 may have been such that light energy was not available. 

 Organisms developing under such conditions must have 

 been directly dependent upon chemical energy. Such 

 energy might be secured by the oxidation of ferrous iron, 

 of free sulphur or of the sulflds (particularly hydrogen 

 sulfid), methane, hydrogen, carbon monoxid and am- 

 monia. Organisms among modern species are known 

 which can utilize each of these methods of securing 

 energy. There is no reason, therefore, why any one of 

 these should not be a method used by a primitive form. 

 The modern types of nru.-mi-m- which oxidize ferrous to 

 ferric iron are in many respects among the most highly 

 differentiated of the filamentous bacteria and show many 

 points of resemblance to the blue-green algae. They show 

 few primitive characters, and are probably to be regarded 

 as not closely related to the primitive bacteria. 



