204 PLANT LIFE. 



dead leaves, insects, the bodies of animals, etc., are 

 broken up in the same way by bacteria, B. 3, and their 

 nitrogenous parts again used by plants. 



Amongst the most interesting members of this group 

 of bacteria, are certain kinds which inhabit peculiar little 

 tubercles on the roots of Clovers, of Whin, and of nearly 

 all plants belonging to the Leguminosae. These, B. 6, 

 belong to the set which obtain nitrogen from the air. 

 On account of the Leguminosae being specially endowed 

 with these nitrate-forming bacteria, their agricultural 

 uses are very important. A crop of Leguminous plants 

 increases the amount of nitrate in the soil ; and, in 

 Germany, these plants are often grown, not for seed 

 or fodder, but merely to be ploughed into the soil 

 whilst still green. By this means the soil is enriched 

 with nitrogenous material, and produces a larger 

 amount of more valuable crops, such as Cereals or 

 Beetroot. It will thus be seen with regard to bacteria : 

 (i) that they lie, literally, at the roots of all plant life, 

 and are probably essential to it ; (2) that they have 

 produced the nitrate deposits of South America ; (3) 

 that they are of extreme importance in the rotting 

 of farmyard manure and of all decaying matter ; (4) 

 that they are specially important for Leguminosae. 



But they are also essential in the following common 

 operations in agriculture: (a) Haymaking, during which 

 bacteria destroy the more perishable parts of the grass 

 leaves and stems. The difficulty in a wet climate lies 

 in the tendency of the putrefaction-bacteria and moulds 

 to develop within the heaps. This results in decom- 

 position, or even in spontaneous combustion, if the 

 hay is stored in a wet condition. The heat within 

 a stack is often 70" C. {b) Ensilage or Silos : Grasses 

 and Herbaceous plants are collected when green, and 



