OF PHOTO-SYNTHESIS 



organic nitrogenous substances. Their very specific reactions show 

 these ultra-microscopic germs to be highly organised systems, on 

 the path from the inorganic to the organic. It is hence futile to 

 seek at the level of bacteria for the origin of the organic; the first 

 stage must have been an inorganic colloidal solution aggregate, 

 capable of utilising sunlight and of building up on its surface or in 

 its meshes organic substances as a forerunner for the still ultra- 

 microscopic living cell. The powers of such a synthesising colloid 

 in evolving more complex forms of matter would soon have been 

 exhausted had it not been able to fix nitrogen as well as carbon from 

 its environment. This power of nitrogen fixation, as evolution 

 proceeded, must necessarily have been passed on to the more highly 

 organised forms as these arose, for without such assimilative power 

 they could not survive in a fresh world containing no ready- formed 

 organic food. 



Just as in carbon fixation, at a certain stage in evolution, a luxus 

 method of fixation was evolved in the chloroplast of the green cell, 

 which was able to work at a higher velocity and use longer wave- 

 lengths of light than the simpler inorganic colloid which preceded 

 it, so in the case of nitrogen the slow union of nitrogen and oxygen 

 to form oxides of nitrogen, induced by sunlight, in inorganic systems, 

 became replaced by more rapid transformers in the unicellular green 

 plant ; and when organic matter began to accumulate, still another 

 luxus channel was opened by those bacteria and other unicellular 

 organisms which can use the supply of energy of decaying non- 

 nitrogenous matter to build up nitrogenous compounds, utilising 

 atmospheric nitrogen for the purpose. Examples of such cases of 

 luxus fixation are the azoto-bacter living free in the soil and the 

 nitrogen- fixing bacteria in the tubercles of the rootlets of the 

 leguminosae. It is obvious, however, that there existed no decaying 

 organic matter at the first dawn of the organic, and that leguminosae 

 and all plants living in symbiosis with nitrogen- fixing organisms are 

 late creations in the evolution of life. 



Interesting and of great practical importance as are these 

 symbioses of a carbon-fixing organism with a nitrogen-fixing organism 

 subsisting upon it or upon its dead products, it is logically quite clear 

 that they cannot have formed the origination of life and are only 

 bypaths of evolution. One of the earliest organisms must have 

 possessed the dual function united in a single cell, or solution 

 aggregate, of fixing both carbon and nitrogen. Approaching the 



