io6 



THE LIFE OF THE PLANT 



such a way that some of the roots are in one vessel, 

 while the rest are in another. The solution in one of 

 the vessels is previously boiled, whereas a small quantity 

 of water, in which soil containing bacteria has been 

 standing, is added to the other. Nodules do not 

 appear on the roots immersed in the boiled and sterilised 

 solution. The fact that the assimilation of nitrogen 



FIG. 31. 



from the air depends upon the presence of such bacteria 

 in the soil can be proved in the following way (fig. 31). 

 A row of glass vessels containing peas are filled with 

 soil deprived of nitrogen, but infected with soil-washings 

 containing bacteria ; while another row are filled with 

 soil sterilised by means of heat, and watered with the 

 same soil-washings previously boiled, and therefore also 

 sterilised. The result is marvellous : it is only plants 



