28 



THEORIES ON THE ABSORPTION OF NITROGEN 



showed they were perfectly correct, and from which they 

 drew the following conclusions : — 



(i) In a sterilized medium without nitrogen content the 

 Leguminos^e show no tubercles and the plants perish. 



(2) In a medium which is unsterilized, but devoid of 

 nitrogen, tubercles are present and the plants do not wither. 



(3) In a sterilized soil containing nitrates the Leguminos^ 

 show^ no tubercles but survive notwithstanding. 



(4) In an unsterilized soil containing nitrogen, nodules 

 are to be observed and the growth is perfect. 



The following table shows facts relating to the production 

 of tubercles under different cultural circumstances and also 

 indicates the extent of assimilation of nitrogen in each case : — 



Experiments to show the Influence of Bacteria on the 

 Formation of Root Nodules. 



24^1 



16-864 



+ 0-348 



In sand provided ivith soil infusion 

 ivithoiil addition of nitrogen. 



f Numerous tubercles ; large and small, 



I old and recent, on all the roots. 



\ As above, somewhat stronger and 



[ more numerous perhaps. 



I Numerous tubercles ; the older kind 

 r a trifle more numerous. 



A number of large protuberances, for 

 the most part still firm and full. 

 Nuhierous others more recent on 

 i the secondary roots. 



No fact can be cited from among these observations to 

 support the theory which regards the tubercles as store- 

 houses for nitrogenous nutriment. This theory is based 

 on the fact of the nodules, like the roots and leaves, 



