FROM rut; AIR BY THE LEGUMINOS^ I9 



elusions, that Hellriegel undertook the work which was to 

 enhghten us. 



\\\Rious Researches ox Xodules. 



The above studies of the power of assimihiting atmo- 

 spheric nitrogen were undertaken simuhaneously with the 

 researches on the nodules of the Leguminosae. 



As we have already seen, the roots of the Leginninosie 

 are characterized by tleshy excrescences which form the root 

 tubercles, or, rather, the nodules. These nodules may vary 

 in form according to the plant sown, but they are fairly 

 constant among individuals of the same species. They are 

 sometimes simply spherical, as in the bean; sometimes oval, 

 as in clover ; elliptical in vetchlings ; elongated ovoid, conical, 

 and occasionally more or less digitate as well. Certain 

 varieties, such as vetches, for instance, are characterized by 

 numerous nodules formed at nearly every swelling. 



Nodules should not be confused with certain galls pro- 

 voked by eel-worms; these are distinguished by their 

 irregular indentations. 



The influence of the conditions under which the plants 

 are grown is an important factor in the formation of nodules, 

 but at the same time they do not act to the same degree on 

 all Leguminosa?. That is the reason whv some occasionallv 

 lack these structures, while others require altogether abnormal 

 conditions to check their formation. 



But what is the nature of these nodules? We should 

 have great difificultv in answering this cjuestion had we not 

 the work of M. Maze, of the Institut Pasteur, to clear up 

 a subject on which scientists were not in agreement. Since 

 we have been able to anah-se brieflv the works dealing with 

 the faculty of plants for fixing atmospheric nitrogen, we 

 shall now state in a few words the various opinions expressed 

 on the question of the nodules. 



In 1687, ^lalpighi, albeit with some caution, declared 

 them to be galls. Treviranus, in 1853, without admitting 



