September, 1909.] 



247 



Scientific Agriculture. 



termed baeteroids, protoplasmic bodies, 

 which after the fourth week show a 

 granular structure, aud later still disin- 

 tegrate to allow the bacilli to fall out. 

 The baeteroids show typical Y shapes in 

 the nodules of Clover, Peas, Beans, and 

 Vetches ; in some clovers they are also 

 club or dumb-bell shaped, but only of 

 late has it been possible to get baeteroids 

 to develop in artificial cultures. With 

 the formation of baeteroids begins the 

 growth of the nodules and the fixation 

 of nitrogen ; when in certain eases ab- 

 normal nodules have been found contain- 

 ing only bacilli no fixation has taken 

 place. 



The important question then arises as 

 to whether there is only a single species 

 of the nodule-forming bacterium, or 

 whether each leguminous plant does not 

 possess, if not a corresponding species, 

 at least a race specialised to co-operate 

 with it. It was early shown that certain 

 leguminous plants— notably Seradella 

 Lupins, and Lucerne — could not always 

 be infected by soil which would inocu- 

 late Clover. It was also shown that, 

 if a particular species like the French 

 Bean were inoculated with bacilli from 

 a Clover nodule, it woidd nob grow as 

 well (in the absence of soil nitrogen) 

 as if it were inoculated with bacilli 

 from a nodule obtained from another 

 French Bean plant. However, when 

 the organisms from the Clover nodule 

 had been tor one generation in a 

 French Bean, they then became as effec- 

 tive on the latter as the original French 

 Bean organisms which had had no known 

 connection with Clover. Thus we may 

 consider as established the existence of 

 distinct races of the nodule organism, 

 capable, however, of acclimatisation. 



Very soon after Hellreigel and Wil- 

 farth's discovery, attempts were made 

 to utilise it by artificially introducing 

 the organisms into soil on which legu- 

 minous plants grew badly. Salfeld, in 

 Hanover, engaged in reclaiming waste 

 heath land by ploughing in successive 

 crops of Lupins, &c, found it of advan- 

 tage to bring soil from fields where such 

 crops had grown previously, and to sow 

 6 to 8 cwt. per acre before the first 

 leguminous crop was taken. Between 

 1888 and 1892 he had achieved many 

 successes in this way on the barren 

 heath land manured only with basic slag 

 and potash salts ; the crop nodulated 

 and gathered carbon and nitrogen from 

 the air, out of which a fertile soil was 

 eventually built up. In order to save 

 the trouble attached to sowing such 

 quantities of soil, Nobbe and Hiltner in 

 1896 introduced artificial cultures of the 

 nodule organisms, growing on a jelly 



made from an extract of the plant stif- 

 fened by gelatine. But in such a 

 medium, rich in nitrogen, the nodule 

 organism grows very slowly and becomes 

 inert, so that for practical purposes this 

 " nitragin " proved a failure. 



Little by little, however, the methods 

 of growing the bacteria artificially were 

 improved, chiefly by the introduction of 

 media containing little or no nitrogen, 

 and in 1903-4. Hiltner put on the market 

 a very effective series of cultures grown 

 on agar-agar containing a little plant 

 extract. 



Moore, of the United States Depart- 

 ment of Agriculture, began about the 

 same time to send out cultures in a dry 

 form, prepared by dipping cotton wool 

 into an active liquid culture of the 

 nodule organism and slowly drying it. 

 When required for use, a fresh prepar- 

 ation was made by putting the wool into 

 a solution of sugar and potassium phos- 

 phate, in which the bacteria would begin 

 to grow. Into this active liquid the 

 seeds could be dipped befoie sowing. 

 Moore's preparations turned out unsatis- 

 factory because the bacteria did not 

 remain alive for long after drying. 

 However, since that time, various im- 

 provements have been made in the 

 methods of growing the nodule bacteria 

 in artificial media, and cultures which 

 retain their activity for a considerable 

 time are now obtainable from all the 

 bacteriological laboratories concerned 

 with agricultural work. Whether solid 

 or liquid, they require to be diffused in 

 a considerable bulk of water or separated 

 milk, which can then be distributed over 

 the land. A better method is to tie the 

 seed in a bag of butter muslin, dip it in 

 the fluid, and then allow the seed to 

 dry somewhat before sowing. The seed 

 should not, however, be allowed to dry 

 for long, or the bacteria are apt to 

 perish. The question now arises whether 

 any practical benefit is to be obtained 

 from such an inoculation of the seed of 

 leguminous crops, and two cases must at 

 the outset be considered. Some soils 

 exist, especially in new countries coming 

 under cultivation for the first time, from 

 which the nodule organism is absent ; in 

 such cases inoculation may be of the 

 greatest possible value and may make 

 the difference between obtaining a crop 

 or none at all. Even in these case3, how- 

 ever, the soil is often without nodule 

 bacteria, because in some way its con- 

 dition is unfit for their survival, so 

 that it is of no use to introduce the 

 organism unless at the same time the soil 

 is made a suitable medium for their 

 growth. Soils entirely without nodule 



