74 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. lxii. 



nitrogen of the air by leguminous plants, you may remem- 

 ber that a very considerable body of evidence was adduced 

 in support of the view that that order of plants possessed 

 the power in virtue of their living in symbiosis with the 

 Bacillus radicicola of Beyerinck, or, as Frank called it, the 

 Ehizobimn leguminosarum. That the Leguminos;e possessed 

 a means of obtaining nitrogen which was denied to other 

 orders, or at least possessed by them in a very subordinate 

 degree, was known for ages ; but it was not until quite 

 recent years, culminating in Hellriegel's experiments, and 

 recorded in 1886, that it was satisfactorily proved that 

 the store of nitrogen which the leguminous plants were 

 able to tap so freely was the uncombined nitrogen of the 

 air, and that this power was associated with the growth of 

 the nodules which that order of plants develop so 

 abundantly upon their roots. Since the publication of 

 Hellriegel's investigation, the formation and function of 

 these nodules have been a subject of scientific research in 

 all parts of the world, and these researches have been 

 chietly devised with the view of testing the accuracy of the 

 symbiotic theory. To the results of such of these researches 

 as have come- under my notice, I wisli now shortly to 

 refer. 



If the roots of the ordinary leguminous plants grown in 

 the open field are examined, it will rarely happen that 

 they are found entirely devoid of nodules. Nevertheless, 

 in certain soils it is not uncommon to find good, healthy 

 specimens that are quite free of nodules, showing that 

 nodules are not absolutely essential to tlieir development. 

 Some genera are niore prone to nodulation than others, 

 and among these the lupine is pre-eminent. The lupine is 

 also distinguished among leguminous plants as best adapted 

 for green manuring, on account of tlie large amount of 

 nitrogen which it is able to assimilate. ]>nt lupines also 

 may be found growing vigorously witliout nodules. 



That the nodules on the roots of leguminous plants are 

 caused by the attack of a micro-organism in the soil is 

 easily proved by growing the plants in a soil that has been 

 sterilised by heat or otherwise, when it is found that no 

 nodules then make tlieir appearance. If to sucli a 

 sterilised soil a few grains of unsterilised soil, or a few 



