Nov, 1897.] BOTANICAL SOCIETY OF EDINBURGH 79 



that the plant contnins within it the means of producing 

 nodules on its roots without having to be dependent on the 

 friendly co-operation of bacteria resident in the soil. More- 

 over, if it were so, it should be possilJe to grow leguminous 

 plants having nodules on their roots, even in a sterilised 

 soil. That, however, is against all experience, for there is 

 nothing on the subject regarding which experimenters are 

 more agreed than that the plants grown in a sterilised soil 

 should have no nodules on their roots. 



Another important observation that militates against the 

 view that the liacteria or bacteroids in the nodule are the 

 direct assimilators of free nitrogen, is that when cultivations 

 of the bacteria are made outside the plant in nutritive 

 media containing organic matter of a suitable kind, they 

 have not been found to absorb atmospheric nitrogen. They 

 live upon the nitrogen contained in the nutritive solution, 

 just as other bacteria do. 



It will thus appear that the view that the free nitrogen 

 assimilation takes place in the chlorophyll cells has by far 

 the most sujiport from experimental facts. 



If that be so, then the store of albuminoid matter found 

 in the nodules has not been brought to the plant as a free 

 gift, — it has been supplied by the plant itself, and the 

 question arises : Is this then a case of symbiosis ? Is it 

 not rather a case of pure parasitism, where the invading 

 organism is preying upon the tissues of its host ? If it 

 could be shown that the host was impoverished thereby, 

 and especially if it were injured, that would be the true 

 name for it; but it is alleged that the host plant is greatly 

 benefited, inasmuch as the stimulus derived from the 

 bacteria enables it to assimilate far more nitrogen than 

 it otherwise could, and that even that which goes to the 

 nourishment of the nodule is only lent it for a time. As 

 soon as the life cycle of the bacteria is over, the nodule 

 falls into a state of decay, and the host reabsorbs the 

 albuminoid matter that he has stored in the nodule as 

 a surplus manufacture. True it is that, in the breaking 

 down of the nodule, some of its contents escape into the 

 soil, but that is regarded as an additional proof of the 

 symbiotic relationship, for the bacteria which escape into 

 the soil remain there, and, for ought wc know, increase 



