THE PHYSIOLOGY OF NUTRITION 



133 



The Bacteria form with the Leguminous plant a life partnership, 

 which is called Symbiosis. That it is an advantage for the 

 Leguminous plants to have the Bacteria living in the soil is 

 certain, for those plants with the best 

 developed tubercles thrive the best. 



The relation of the Bacteria with 

 the plants which belong to the Bean 

 family is so well known that farmers 

 can now obtain Bacteria to mix with 

 the seeds of the above plants when 

 sowing. This material which is 

 mixed with the seeds receives the 

 name of nitragm. If a little soil 

 from a field "where plenty of root- 

 tubercles are produced be taken and 

 applied to a soil which will not pro- 

 duce root-tubercles, these will then 

 be produced, and the plant will be- 

 come strong and healthy. 



EXIT. 1 20. Pull up a well-developed 

 Clover plant and examine the roots. 

 Note 



(i) The tubercles on the roots. These 

 are shown in Fig. 155. 



(ii) Cut a transverse section of a root 

 so as to pass through a root tubercle and 

 examine it with a hand-lens. 



(iii) Mount a transverse section of a 

 root having a root-tubercle in water. 



(iv) Examine under a high power, and 

 note the structure. 



EXPT. I2i. Pull up a stunted Clover 

 plant and examine the roots. Note 



(i) The roots have either only very few 

 tubercles or they are entirely absent. FIG. 155. Root-tubercles on the 



(ii) The general appearance of the roots of a Leguminous plant, 

 plant. 



(iii) Experiments 120 and 122 show 



that the tubercles exert a favourable influence on the growth of the 

 Clover. 



EXPT. 122. Prepare two plant pots in the following way (a) Fill 

 one with rich soil from a field in which Clover grows to perfection ; 

 (b) fill the other one with sand which has been raised to a high 



