THE MAIN TYPES OF SOIL 69 



practice, or when investigated scientifically 

 by unprejudiced inquirers, such cultures 

 have proved to be of little, if any, account, 

 and at the moment one hears but little of 

 them. While it is certain that leguminous 

 plants cannot attract colonies of bacteria 

 to their roots unless the bacteria are present 

 in the soil, it would appear that practically 

 all soils contain the necessary organisms 

 in abundance, and that the addition of 

 further supplies is unnecessary. It has also 

 been alleged that each leguminous plant can 

 only associate itself with its own particular 

 organism, or with one that is very closely allied. 

 It is maintained, for instance, that nearly- 

 related leguminous plants, such as white and 

 alsyke clovers, are capable of attracting the 

 same variety of organism, whereas species 

 standing wide apart, like beans and medick, 

 have no mutual interest in any particular 

 organism. But common observation will fur- 

 nish evidence that this cannot always be the 

 case. In the Weald of Surrey, for example, 

 it is the rarest thing to find broom or lucern, 

 and we should therefore be asked to assume 

 that the organisms on the roots of these 

 plants cannot naturally be present in such 

 soils, so that, should an attempt be made to 

 cultivate these plants, successful growth is 



