62 THE SPIRIT OF THE SOIL 



the bacteria. In much the same way it has been 

 found that seeds may be able to resist inoculation 

 this difficulty in practice can be easily overcome 

 owing to a protective chemical substance which 

 prevents the bacteria from digesting the cell wall and 

 forcing an entry: a phenomenon roughly analogous 

 with the fact that the cells of the stomach and 

 intestines possess chemical substances that prevent 

 their being attacked by the digestive ferments pre- 

 pared in the alimentary canal. In such a case 

 inoculation is obviously useless. 



From several standpoints a great deal depends on 

 the health and vigour of the root. As we have seen, 

 if the root is very vigorous the bacteria cannot enter 

 it, and in such conditions leguminous crops planted 

 in the soil, instead of enriching it in nitrogenous 

 bodies, would deplenish its store of Nitrogen. 

 Suppose, however, that one goes to the other 

 extreme, and that the plants are starved and feeble. 

 In such a case the roots can put up no resistance to 

 the bacteria. These will force an entry, but the 

 roots, instead of giving harbourage only to the most 

 vigorous bacteria, will admit even the weaker strains, 

 such, perhaps, as will be sluggish in forming nitrogen 

 compounds, and in consequence the plants will gain 

 little from their association with the bacteria. It has 

 even been suggested by some bacteriologists that the 

 just balance may be overset and the bacteria become 

 too strong for the plants, and the latter be unable to 

 insist on the former fulfilling their side of the con- 

 tract and giving up a fair share of the nitrogen com- 

 pounds that they have prepared. In such a case 



