OCTOBEK 13, 1905.] 



SCIENCE. 



451 



come entirely modified by growing on par- 

 ticular media, or at a high temperature, 

 and even by long-continued growth under 

 laboratory conditions. 



B. radicicola does not develop very freely 

 on the ordinary media used for the cultiva- 

 tion 'of bacteria, nor can it be made to fix 

 much free nitrogen when removed from the 

 host plant. In particular it is maintained 

 that the medium used, gelatine with an 

 infusion of some leguminous plant, causes 

 the organism to lose, to a very large extent, 

 its power of fixing nitrogen, because it 

 contains so much combined nitrogen. G. 

 T. Moore, for instance, says: "As a result 

 of numerous trials, however, it has been 

 found that although the bacteria increase 

 most rapidly upon a medium rich in nitro- 

 gen, the resulting growth is usually of very 

 much reduced virulence; and when put 

 into the soil these organisms have lost the 

 ability to break up into the minute forms 

 necessary to penetrate the root-hairs. They 

 likewise lose the power of fixing atmos- 

 pheric nitrogen, which is a property of 

 the nodule-forming bacteria under certain 

 conditions." Latterly the subcultures 

 have been made on media practically free 

 from nitrogen, on agar agar, for example, 

 or on purely inorganic media, supplied, of 

 course, with the carbohydrate, by the com- 

 bustion of which is to be derived the energy 

 necessary to bring the nitrogen into com- 

 bination. 



In example of the two preparations now 

 being distributed on a commercial scale, 

 the one sent out by Professor Hiltner, of 

 the Bavarian Agricultur-botanische An- 

 stalt, consists of tubes of agar which have 

 to be rubbed up in a nutrient solution con- 

 taining glucose, a little peptone, and vari- 

 ous salts, and this after growth has begun 

 is distributed over the soil or the seeds 

 just before sowing. Moore, of the U. S. 

 Department of Agriculture, finding that 

 the bacterium will resist drying, dips 



strands of cotton-wool into an active cul- 

 ture medium and then dries them. The 

 cotton-wool is then introduced into a solu- 

 tion containing maltose, potassium phos- 

 phate and magnesium sulphate ; in a day 

 or two growth becomes active, and the solu- 

 tion is distributed over soil or seed. 



It is too early yet to determine what 

 measure of success has been attained by 

 these inoculations with pure cultures; but 

 in considering the results a sharp distinc- 

 tion must be drawn between their use on 

 old cultivated and, such as we are dealing 

 with in the United Kingdom, and under 

 the conditions which prevail in new coun- 

 tries where the land is often being brought 

 under leguminous crop for the first time. 

 Few of our English fields have not carried 

 a long succession of crops of clover, beans, 

 vetches and kindred plants ; the Bacterium 

 radicicola is abundant in the soil; and, 

 however new the leguminous plant that is 

 introduced, infection takes place unfail- 

 ingly, and nodules appear. It is true that 

 the organism causing nodulation may not 

 belong to the particular racial adaptation 

 most suited to the host plant, and that in 

 consequence an inoculation from a suitable 

 pure culture might prove more effective. 

 Again, it is possible that even a plant like 

 clover, which would be infected at once 

 through the previous growth of the crop, 

 might be made a greater collector of nitro- 

 gen through the introduction of a race of 

 bacteria which had acquired an increased 

 virulence ; but in either of these cases the 

 most that could be expected from the in- 

 oculation would be a gain of 10 per cent, 

 or so in the crop. This great, though 

 limited, measure of success depends upon 

 two things — on obtaining races of B. 

 radicicola possessing greater virulence and 

 greater nitrogen-fixing power than the nor- 

 mal race present in the soil, and again on 

 the possibility of establishing this race 

 upon the leguminous crop under ordinary 



