SOIL ORGANISMS 395 



teria. The organic matter of the soil, consisting as it does of 

 the remains of a large variety of substances, furnishes a suit- 

 able food supply for a very great number of forms of organ- 

 isms. The action of one set of bacteria on the cellular matter 

 of plants embodied in the soil produces compounds suited to 

 other forms, and so from one stage of decomposition to another 

 this constantly changing material affords sustenance to bac- 

 terial flora, the extent and variety of which it is difficult to 

 conceive. A soil low in organic matter usually has a lower 

 bacterial content than one containing a large amount, and, 

 under favorable conditions, the beneficial action, to a certain 

 point at least, increases with the content of organic substance ; 

 but, as the products of bacterial life are generally injurious 

 to the organisms producing them, such factors as the rate 

 of aeration and the basicity of the soil must determine the 

 effectiveness of the organic matter. 



The so-called acidity of the soil is probably as important 

 a factor in bacterial activity as it is to higher plants.. In 

 general, favorable soil organisms of all kinds seem to func- 

 tion better in a soil carrying sufficient active base to generate 

 conditions favorable for higher plants.^ An exception some- 

 times occurs, however, notably in the case of the ' * finger-and- 

 toe'^ disease of certain Cruciferse, which is retarded by 

 liming. 



The activities of many soil bacteria result in the formation 

 of acids which are injurious to the bacteria themselves, and 

 unless there is present some base with which these can com- 

 bine, bacterial development is inhibited by such products. 

 This is one of the reasons why lime is so often of great benefit 

 when applied to soils, and especially to those on which alfalfa 

 and red clover are growing. For the same reason the 

 presence of lime hastens the decay of organic matter in 

 certain soils, and the conversion of nitrogenous material 

 into compounds available to the plants. As showing the 

 value of lime in the process of nitrate formation it has been 



