BIOLOGY OF SOILS 149 



on the kind of plants from which they were originally 

 derived. It is in this adaptability, or capacity for modifi- 

 cation, that the greatest hope of future practical develop- 

 ments lies. The bacteria may be modified by cultivation, 

 as higher plants have been, and forms or varieties suitable 

 for purposes of practical utility may be produced. 



The bacteria required for the commoner kinds of legu- 

 minous crops, e.cj., clovers, vetches, etc., are probably pre- 

 sent, in active form, in all the cultivated soils in this 

 country that are adapted for the growth of these plants. 

 It is by no means certain, however, that the microbes re- 

 quired for other plants are so plentiful. Should any diffi- 

 culty be experienced in raising a leguminous crop on a 

 soil on which it has not previously been grown, it may 

 possibly be due to absence of the necessary bacteria. If 

 the difficulty be not due to other obvious causes, such as 

 lack of lime, phosphates, etc., inoculation of the soil should 

 be tried. In some cases it has proved useful. 



As a means of stimulating the growth of crops on soils 

 which already contain the necessary bacteria, the outlook 

 is, perhaps, less promising. Numerous experiments are, 

 however, being carried on, and developments of practical 

 importance are hoped for in the future. The following 

 results were obtained in the soil inoculation experiments 

 at Eothamsted in 1907 : 



EFFECT OF INOCULATING THE SOIL UPON TUB GROWTH OF LEGUMINOUS 

 PLANTS. PRODUCE OF KBD CLOVER (HAY), 1907. 



