Feb. 1S97.] BOTANICAL SOCIETY OF EDINBURGH 89 



Experimenters will also note — 



1. That the cultures are very sensitive to light, and 

 heat, and drought, all of which destroy the efficacy of the 

 bacteria. Therefore do not allow the inoculated soil or 

 seed to become too dry, and do not allow the seeds to 

 remain exposed on the surface. 



2. The results of inoculation must not be looked for too 

 early. Eemember that the efficacy of the nodules only 

 comes into full activity when the soil nitrogen has been 

 used up. The more of this in the soil the later will the 

 effects of inoculation show themselves. 



3. In order that a proper judgment be passed as to the 

 effect of inoculation in parallel experiment, a mere naked eye 

 overlook is not sufficient and not trustworthy. There must 

 follow a careful weighing. Dr. Hilltner told me of a case 

 where Dr. Salfeld made an experiment with ornithopus, 

 the pure cultures for which were supplied from Tharand. 

 When, towards the end of the experiment, an inspection was 

 made, there seemed, as far as the eye could judge, to be 

 no difference between the inoculated field and the non- 

 inoculated, and, as the plants in the latter also showed 

 nodules, everyone thought this experiment had proved a 

 failure. Just eight days after the inspection, the two 

 crops having been cut in the interval, Dr. Salfeld wrote to 

 Professor Xobbe to the effect that the inoculated plot had 

 borne stronger plants than the non-inoculated, and that a 

 careful weighing had given a twenty-five per cent, advan- 

 tage in green substance to the inoculated over the non- 

 inoculated. 



4. It must not be forgotten that the condition of the 

 soil has a most important influence on the results of 

 inoculation. The — apart from nitrogen — necessary plant 

 foods must be present in sufficient quantity. The nodules 

 collect only nitrogen, so that the plants must find in the 

 soil all the other foods. A chain has only the strength of 

 its weakest link, and " a field is as poor as its most 

 deficient fertilising principle." Apart from nitrogen, if 

 there be only one of the other necessary foods not 

 present in sufficient amount, then the capacity of the 

 nodules will fail from the time when this substance 

 begins to disappear. 



