Improving the Chemical Nature of the Soil 89 



125. Tubercles on Legumes. Plants belonging to the 

 pea or legume family have small tubercles on their roots. 

 (Fig. 47, A and B.) On opening the small tubercles found 



Fig. 47. A, root system of pea with tubercles. B, root system of alfalfa with 

 tubercles. After Belzung 



on the roots of beans, peas, alfalfa, blue bonnets, etc., 



we notice in the center a rose-colored area. If a bit 



of this is scraped into a drop of water, it becomes milky 



because of the hundreds of bacteria. 



They are so small that the most powerful 



microscopes are needed to make out their 



form. (Fig. 48.) It is these little plants 



that have the power to take the free 



nitrogen of the atmosphere and convert 



it into such form that the nodule-bearing 



plants, such as the cow-pea, may use it. 



Without these bacteria the legumes do not 



fix free nitrogen. It is this nitrogen-fixing 



power that makes these plants so valu- Fl fuberc?e U of ro iS 



fn gume showing 



W US. the bacteria. 



