FORMATION OF ORGANIC SUBSTANCES I13 



Zeus ". This implies that the autotrophs must suddenly have 

 appeared in an inorganic medium, completely equipped 

 with the most complicated biochemical systems and morpho- 

 logical structure required for the autotrophic synthesis of 

 organic substances. 



The extreme complexity of organisation of those living 

 beings which are capable of photosynthetic assimilation of 

 carbon dioxide is evident not only to the biochemist but also 

 to the morphologist. It long ago forced itself on the attention 

 of the botanical systematists. On purely morphological 

 grounds many of them denied that such organisms could be 

 the prime ancestors of life on the Earth. Others, ho^s^ever, 

 assigned to this role one or another of the more primitive 

 groups of photo-autotrophs because they imagined that the 

 primaeval living beings must have been capable of main- 

 taining themselves on inorganic substances. In this they 

 paid insufficient attention to the facts of comparative mor- 

 'phology, or even flew in the face of these facts (see, for 

 example, the review by A. Pascher^^). 



The inherent weakness of this position was very much 

 felt by a number of biologists during the closing years of the 

 nineteenth century. Consequently, when S. Vinogi'adskii 

 discovered the chemosynthetic bacteria, they were quick and 

 keen to proclaim these as the primaeval organisms. This 

 seemed to resolve the dilemma that, while the primaeval 

 organisms must, according to prevailing views, have been 

 autotrophic in their nutritional requirements, the organisa- 

 tion of cells capable of photosynthesis is manifestly far from 

 primitive. 



The hypothesis that the chemoatitotrophs were the first 

 organisms to inhabit our planet has remained current up to 

 the present time and is to be found in several widely read 

 revicAvs (e.g. those of C. H. Werkman and H. G. Wood,^'* 

 M . Stephenson,^^ W. O. Kermack and H. Lees"^ and others). 

 In the light of present-day biochemical knowledge, how- 

 ever, the facts suggest that chemosynthesis, like photo- 

 synthesis, requires a far more complicated and specialised 

 biochemical organisation than does heterotrophy (the use of 

 preformed organic substances). Chemoautotrophs can make 

 use of organic substances; this ability is fundamental to the 



