Nov. 1896 ] BOTANICAL SOCIETY OF EDINBURGH 1 5 



and an occasion like this is an appropriate one for the 

 purpose. Time will not permit me to do more than trace 

 its salient features in brief outline. 



The gist of Hellriegel's discovery is this, — he found that 

 leguminous plants of the sub-order Papilionacea3 were able 

 to make their albuminoid matter by assimilating the free 

 nitrogen of the air, and that that power was associated in 

 some way with the growth of warty tubercles on the roots 

 of the j^lants, and that these tubercles contained peculiar 

 cells called bacteroids, due to the agency of bacteria which 

 entered the roots of the plant from the soil. 



I shall explain how he came to the full possession of 

 that knowledge immediately, but in the first place I 

 would like to refer shortly to the tubercles or nodules 

 themselves. 



Hellriegel did not discover the nodules. They have 

 been known for a long time. The first mention of them 

 that I am aware of was made by the famous Italian 

 anatomist Malpighi, who described them in the year 1660. 

 He thought they were galls, but he was surprised to find 

 that they never contained eggs or larvae. Coming to recent 

 times, Treviranus describes them in a paper communicated 

 to the Botanische Zeitung in 1853, but the first careful 

 description of them was made by Woronin in 1866. He 

 studied those found on the roots of Alnus glutinosa and 

 Ziqnnus mutabilis. He described them as consisting of 

 two distinct kinds of parenchymatous tissue, an inner and an 

 outer, separated by a layer of vascular bundles proceeding 

 from the vascular bundles of the root of which they were 

 lateral excrescences. He noticed that the outermost cell of 

 the inner parenchyma multiplied by division, and that the 

 •older cells contained a slimy mass of plasma, full of tiny 

 little bacteria-looking bodies, which, when put into water, 

 moved about just as bacteria do, and he thought that they 

 were the cause of the nodules. 



Erikssen, in 1874, published a paper accurately de- 

 scribing the development of the nodules on the roots of 

 the Faha vulgaris, and observed that the region where the 

 bacteroids were rapidly multiplying by division was entered 

 by the hyphfe of a fungus, which appeared like a knotted 

 thread ramified through the mass. 



