116 THE PRACTICAL SIDE OF 



grow clover itself and other plants of the 

 leguminous order in sterile sand to which 

 mineral fertilisers alone were supplied. 

 When, however, a small quantity of fertile 

 soil was added as a watery extract to the 

 sand, the still-living plants continued 

 to grow and mature, assimilating atmo- 

 spheric nitrogen. On the roots of these 

 plants small clusters of nodules were found, 

 which may be also found upon the roots 

 of the leguminous plants of the farm which 

 are growing under ordinary conditions. These 

 nodules were found to contain bacteria now 

 known as Bacteria Radicicola. Thus, these 

 organisms live in symbiosis or cohabitation, 

 as it were, with the plants on the roots of 

 which they exist for mutual benefit. 



A simple experiment will prove the above 

 facts to be true. If a few seeds of the clover 

 plant, or the pea, are placed in sterilised sand 

 in a flower-pot, they will germinate and grow 

 until they have exhausted the reserve food 

 which the seed contains, when, having nothing 

 to fall back upon to continue the life process, 

 they die. If, however, the sand is supplied 

 with mineral plant foods, and a small quantity 

 of the soil-extract to which we have referred, 

 the young plants will continue to grow to 



