chap, v The Discovery of Chemosynthesis 371 



hydrogen only traces of ammonia and nitric acid, with as 

 little as -0005 per cent, of organic material. Sugar, peptone, 

 asparagin, and similar compounds rapidly kill the plant, 

 even when present in little more than traces. 



There are several genera and species of these sulphur 

 bacteria, some of which were described as long ago as 

 1840, but their chemosynthetic powers were not known 

 till the appearance of Winogradsky's researches. 



Winogradsky attributed a similar activity to another 

 group of bacteria, which have the power of utilizing ferrous 

 carbonate, and which are commonly alluded to as the 

 iron bacteria. These were first described by Cohn in 1870. 



These phenomena leave no doubt that the constructive 

 power of protoplasm is much greater and more varied than 

 was supposed by the writers of the early years of our 

 period. Consideration of them points to the possibility of 

 synthetic processes in the higher green plants without the 

 intervention, or at any rate the immediate influence, of 

 light and chlorophyll. The story of the fixation of nitrogen 

 from various antecedent compounds, which we have already 

 considered, leads to the conception of very extensive chemo- 

 synthetic powers in the ordinary green plant, called into 

 action perhaps only after preliminary activity of the chloro- 

 phyll apparatus, and not extending to carbohydrate forma- 

 tion, but no less real in the green plant than in the humble 

 organisms in which they seem to set up the only synthetic 

 process. 



Aa 2 



