The First Land Plants 



gas nitrogen and sharing it with the nostoc* In return 

 the nostoc gives up some of its sugary material or 

 other product of carbonic acid to the bacterium. 



The best way is to consider the two as friends (as 

 one would understand this term in the City), that is, 

 " business " friends. 



The whole group of fungi were very likely at one 

 time green algae. Some of them, like the colourless alga, 

 choreocolax, mentioned in the last chapter, found out 

 a simpler and easier way of living as parasites, clinging 

 to and devouring other algae. 



One might almost suggest that they trained them- 

 selves by the destruction of many green algae until 

 they became specialists and very expert in absorbing 

 food material. At any rate fungi and especially bac- 

 teria are nowadays experts in the work of getting 

 nitrogen and other salts from any kind of material, 

 whether living or dead. 



Somehow or other the azotobacter or its ancestors 

 discovered how to seize the nitrogen of the air and 

 turn it into nitrates and nitrites. 



The two together, the nostoc and azotobacter, work 

 as a co-operative company. They are now a mutual 

 blessing ; both benefit from the association, but yet, 

 like some business friends, they are apt to become 

 parasites, and require to be carefully watched. 



After the discovery of azotobacter or nostoc, the 

 mud of almost every ocean was searched for this 

 interesting germ, and it has been found in Java, in East 

 Africa, in Heligoland, and in the Baltic. f 2 Swarms of 



* Nitrogen, sulphur, carbon, coal, and peat are all oxidised by bacteria. 

 How it is done, no one has explained. Nitrates are formed in the atmosphere 

 by electric discharges (lightning flashes). Is it possible that bacteria produce 

 it by electrical activity ? 



+ Bacteria occur in small numbers in sea-water, but not apparently below 

 loo fathoms deep. 



44 



