The Symbiosis 213 



The nature of the nodules. — For some years there 

 existed among botanists and bacteriologists a difference 

 of opinion as to the true nature of the nodules. It was 

 held by some persons that they are the result of some 

 disease in the roots. Others thought that they are 

 thickened modifications of the healthy roots. Still 

 others regarded them as storage places for reserve food 

 materials. Among the latter was the German, Brun- 

 chorst, who saw in the bacteria>-like particles only re- 

 serve protein bodies and named them "bacteroids" 

 (which means bacteria-like). Hellriegel asserted that 

 the nodules are due to infection from without, caused 

 by bacteria; but, that these invading bacteria are not 

 disease germs and inflict no injury upon the host-plant. 

 He regarded the relation established between the host- 

 plant and invading bacteria as advantageous to both, 

 and, therefore, an instance of symbiosis. 



A further step in advance was made by the investi- 

 gations of Beyerinck and also of Prazmowski. The for- 

 mer demonstrated that the bacteria-like bodies in the 

 nodules are true bacteria, by growing them artificially 

 on various substances outside of the legume roots. Praz- 

 mowski showed that the roots of legumes could be arti- 

 ficially infected by such laboratory cultures and nodules 

 produced thereby. It was thus firmly established that 

 the nitrogen-gathering power of legumes is due to their 

 ability to form a partnership with certain species of 

 soil bacteria, named by Beyerinck Bacillus radicicola. 

 This partnership is mutually profitable, the bacteria 

 furnishing nitrogen compounds to the plants, while the 

 latter provide sugar and various mineral salts to the 



