directly upon the nitrogen brought to them from 

 the air by rain-water, and this by the aid of certain 

 bacteria at their roots. On the roots of the pea, 

 for instance, we often find numerous tubercles; 

 these used to be thought to be evidence of disease, 

 and the microscope seemed to corroborate this by 

 showing them to be filled with micro-organisms 

 (bacterium radicicolus). However, it was soon as- 

 certained that instead of causing harm to the pea 

 plants these colonies of bacteria contributed very 

 largely to their welfare. They actually fed the 

 plants with nitrogen through their roots. If peas 

 are planted in a soil which has been washed and 

 calcined to deprive it of its nitrogenous com- 

 pounds, they will soon become sickly and die; but 

 if some water is made muddy with a little soil in 

 which healthy peas are growing, and soaked to 

 their roots, they become healthy and thereafter 

 flourish. The water carries to their roots some of 

 the bacteria from the ground in which the healthy 

 peas are growing. These micro-organisms attach 

 themselves to the roots, and while living, in a 

 measure, upon the nutrition in them, more than 

 pay for what they eat by giving to the plants 

 through their roots quantities of nitrogen, taken in 

 some mysterious manner from the air brought to 

 the soil by the water. Let us wonder if electricity 

 may not help in this matter by stimulating the 

 activity of these bacteria, for it is said to favor 

 very much the growth of peas when applied to the 

 soil. Before directing our attention to the question 

 of the action of electricity upon bacteria, let us 



