Scientific Agriculture. 



328 



[October, 1909. 



edly been proved to be highly bene- 

 ficial, but on the majority of cultivated 

 soils it was not evident that inoculation 

 had been attended with any benefit. 



With the extension of experiments 

 similar to those of Salfeld, one or 

 two disadvantages connected with this 

 method of soil inoculation began to 

 make themselves felt. The transport of 

 large quantities of soil from one district 

 to another was natuially expensive- 

 Injurious fungi, together with weed 

 seeds, might be introduced into the 

 soil, with the desirable bacteria. These 

 considerations, combined with the fact 

 that the nitrogen-assimilating organisms 

 could be isolated from the root nodules 

 of legumes, and cultivated on various 

 artificial media, led to greater attention 

 being paid to the possibilities of inocu- 

 lation with pure cultures of the Pseudo- 

 monas bacteria, and in the past twelve 

 years or so, a number of preparations, 

 all containing this organism, have been 

 brought forward for soil inoculation 

 purposes. 



In this connexion there arises a question 

 which is obviously of considerable im- 

 portance in influencing the success of 

 any effort at soil inoculation, but which 

 has not yet been definitely settled. This 

 question relates to the identity of the 

 various bacteria which are found living 

 in association with different species of 

 Leguminosse. Much investigation has 

 been done with the object of: ascertain- 

 ing whether all the organisms living in 

 symbiosis with various agricultural 

 leguminous crops are identical with 

 Pseudomonas radicicola, first isolated by 

 Beyerinck from pea plants, whether the 

 different kinds are varieties of this 

 species, or whether there are different 

 species associated with particular plants. 

 Colonies of bacteria cultivated from root 

 nodules from different species of legume 

 show many points of similarity, but also 

 some points of difference. 1 n early experi- 

 ments carried out by Hellriegel, it was 

 seen that a watery extract of soil on which 

 clover and beans had been grown was 

 instrumental in inducing nodule forma- 

 tion on clover and bean seedlings grown 

 in sterile sand, but had no effect what- 

 ever on serradellaand lupin plants grow- 

 ing under the same conditions. When 

 an extract from a sandy soil which had 

 just previously borne the latter plants 

 was added, however, the serradella and 

 lupins formed nodules on their roots 

 and grew apace. Hellriegel therefore 

 concluded that there were essential 

 differences between the bacteria from 

 the various legumes. The evidence that 

 has since been brought forward seems 

 to point to the view that all the bacteria 

 inhabiting the root tubercles of legu- 



minous plants, whicn are the agency of 

 nitrogen assimilation from the air, 

 belong to the species Pseudomonas 

 radicicola, but that if this organism is 

 grown for some time continuously in 

 association with one kind of plant only, 

 it becomes so modified as to be specially 

 adapted to give the best results with 

 this species alone, and loses its efficiency 

 in greater or less degree for all other 

 kinds of legumes. Experiments conduct- 

 ed by Nobbe and Hiltner orove that the 

 best results from inoculation can only 

 bp expected when the crop grown is 

 inoculated with bacteria from the same 

 species of plant. 



As already mentioned, pure cultures of 

 the root nodule bacteria had been pre- 

 pared on various artificial media, and in 

 1896, two Germans, Messrs. Nobbe and 

 Hiltner, developed this idea on a com- 

 mercial scale. Cultures of the organ- 

 isms, grown on a gelatine medium, 

 were started by infection from root 

 tubercles from the different leguminous 

 plants cultivated as field crops, and this 

 preparation was placed on the market 

 contained in small glass bottles, under 

 the name ' Nitragin.' In using the 

 nitragin for inoculation purposes, the 

 nutrient jelly was to be dissolved 

 in a quantity of lukewarm water, 

 and the solution sprinkled over the 

 seed, thorough distribution of the 

 bacteria being ensured by this means. 

 The seed was then to be dried before 

 planting. 



The merits of nitragin were thoroughly 

 tested at experiment stations and on 

 private farms both in Europe aud 

 America. It was hoped that the pre- 

 paration would supply not only nitrogen- 

 gathering bacteria to soils lacking 

 these organisms, but bacteria of a 

 high degree of efficiency. Although 

 in the first two seasons a few favourable 

 reports on the results obtained from the 

 use of nitragin were received, by far 

 the greater majority of the returns sent 

 in were of a negative character, and 

 briefly, it may be stated that the pre- 

 paration turned out to be a distinct 

 failure. It seemed after all that the 

 pure culture method of inoculation, 

 from which so much had been expected, 

 was less reliable than the older plan ot 

 introducing the nitrogen-gathering 

 organisms by distributing a supply of 

 fertile earth from fields that ha 1 lately 

 borne flourishing legume crops. 



Despite the unsatisfactory results 

 which followed the first attempt to 

 establish the use of pure cultures of 

 Pseudomonas radicicola as the stand- 

 ard means of inoculation, the matter 

 still continued to receive a good deal 



