Nov. 1897.] BOTANICAL SOCIETY OF EDINBUKGH 83 



These quantities are more than ten times as great as that 

 assimilated by the plants grown in the sterilised and un- 

 inoculated soil. The result of this experiment is to show 

 that inoculation is of use in a sterilised soil protected from 

 air-borne organisms. In that case the inoculation and 

 the nodulation resulting therefrom increased the nitrogen 

 assimilation eightfold, but, in the case of an unsterilised 

 and unprotected soil, inoculation and consequent nodulation 

 made no difference whatever. 



The explanation of this unexpected result is that the 

 soil of the unsterilised pots was thickly grown with algie, 

 and well supplied with bacteria ; and it is to the activity 

 and nitrogen-assimilating power of these that the plants 

 owed their increased assimilation. In other words, the 

 plants received their nitrogen from the soil, and that 

 nitrogen was brought into the soil from the air by the 

 algffi and bacteria which flourished there. If this be the 

 true explanation, it does away entirely with the symbiotic 

 relation supposed to exist between the Leguminosie and the 

 bacteria contained within the nodules. We are still left 

 with the fact that nodulation is due to the interference of 

 bacteria, and that the nodules are highly nitrogenous bodies 

 whose nitrogen, however, is entirely derived from the plant, 

 and utilised eventually by it for the growth of its own seed, 

 should the plant ever arrive at the seeding stage. If that 

 is all, the attack of the bacteria on the roots, and its 

 subsequent lodgment there in the form of a nodule, must 

 be regarded as pure parasitism, and that the plant eventually 

 absorbs the organic matter of the parasite in its mature 

 stage is due to its having sufficient vigour to confine the 

 parasite within a nodule, and so to limit the sphere of its 

 mischief. 



Whether, in the event of the plant's not possessing that 

 vigour, the bacteria would get the upper hand of it and 

 kill it down, is a probability that has been suggested, but 

 of which I have no proof. 



It is evident, however, that such a condition of matters 

 may occur, and it may, upon further investigation, shed 

 some light on the mysterious disease of clover sickness, and 

 of some other apparently parasitic disease to which some 

 leguminous crops are liable. 



