The First Land Plants 



this valuable azotobacter were found nestling in the 

 slimy surfaces of ordinary seaweeds, living on their 

 sugar (mannite) and supplying them with nitrogen.^ It 

 even occurs on the exquisite fresh-water alga, volvox, 

 whose little hollow spheres of bright green cells re- 

 volve cheerfully in the water to the vigorous wrigglings 

 of its myriads of small oar-like cilia. 



Before this discovery, it had been known that some 

 bacteria had this power of obtaining nitrates. There 

 are especially certain forms which live on decaying 

 vegetable matter in garden soil or amongst leaf mould 

 which accumulate nitrates. Of these the most im- 

 portant are Closterium Pasteurianum (discovered by 

 Winogradsky) and the '' alinite " bacillus of Kruger. 



Of course in practical agriculture such microbes are 

 of the greatest importance. It was not long before 

 people became enthusiastic over the fascinating ideal 

 of sowing bacterial seed and so adding, inexpensively, 

 an enormous increase to the fertility of the soil. But 

 the alinite bacillus has not yet been domesticated; it 

 has only been kept in activity. 



Another nitrate-forming bacillus has been recently 

 very well advertised in the English papers. Its history 

 is most interesting. Pliny was aware that certain crops, 

 peas, beans, and lupines, improve the fertility of the 

 soil instead of impoverishing it. *'The Bean . . . 

 fertilises the ground in which it has been sown as well 

 as any manure." This fact was also mentioned by 

 Thaer in 1809, and has been completely confirmed by 

 the experiments of Lawes, Gilbert, and Pugh.* 



So a simple method of enriching the soil came into 

 use which consists in sowing down peas, lupines, or 

 other legumes, and ploughing them into the soil. This 

 is quite a common practice in Germany. 



For instance, 224 kilos, (about 4^ cwt.) of nitrogen 



45 



