1904.] 



Experiments in Soil Inoculation. 



349 



time, however, investigators have not been idle, and the present 

 position of the subject is to be found in a recent report 'by 

 Hiltner and Stormer.* 



It was early recognised that the organisms (bacteria) which 

 inhabited the root-nodules of the various species of Leguminosce 

 were not all alike, and that, in fact, they showed marked physio- 

 logical if not morphological distinctions. Any particular species 

 of leguminous plant is found to resist more or less successfully 

 the attempt of these various organisms to effect an entrance into 

 its root-hairs, and according to the power of the organism to gain 

 access, and to establish colonies, so is the particular plant bene- 

 fited and the stock of fixed nitrogen increased. This power 

 of adaptability of the organism is designated its "virulence," a 

 term, however, which is perhaps hardly suited to our English 

 mode of expression, though it may for the present be retained. 

 It has been found that organisms of what is called " high viru- 

 lence" are capable of entering with ease the root-hairs of vigorous 

 plants at an early stage of their growth, and of inducing the forma- 

 tion of nodules that are large, numerous, and placed high up on 

 the roots. Organisms of low virulence, on the other hand, can 

 only enter plants of feebler growth, or plants that have passed 

 the most vigorous stage of youth, so that the nodules, in this 

 case, are small and scarce, and distributed, for the most part, 

 near the ends of the roots. The practical object, therefore, 

 would appear to be the breeding of strains or varieties of 

 organisms of high virulence, adapted to the symbiotic require- 

 ments of the various important species of farm and garden 

 leguminous crops. 



The nitragin put on the market a few years ago was used in 



two ways, being either applied directly to the fields, or mixed 



with water and brought into contact with the seed before sowing. 



Under the former method of procedure an increase of crop was 

 obtained only when the nitragin was used on land containing 



much humus. The explanation given for failure under other 



conditions was that the bacteria artificially introduced perished 



for want of food before the leguminous seed germinated and 



produced plants. 



* "Bericht uber neue Untersuchungen iibtr die Wurzelknollchen der Leguminosen 

 und deren Erreger," Arbeitcn cuts aer B10I. Alt'M. fur Land-itnd Forstxvirtschaft 

 am K. Gesunaheitsamtc, Band iii. Heft 3. 



