34 TRANSACTIONS AND PKOCEEDINGS OF THE [Sess. lxi. 



Xobbe and Hilltuer, however, emphasise that the 

 cultures from different Leguminostf have not to be looked 

 on as different bacterial species, but only as adaptable 

 forms, forms adapted to the varying leguminous species by 

 their living on ditlerent plants. To make this clear, they 

 have coined a new phrase — neutral bacteria, viz. those 

 living in the soil with no special biological adaptability to 

 any special leguminous species, but able to get in a weak 

 degree into symbiosis (partnership) with all genera of 

 Leguminos;e. These neutral bacteria, having penetrated the 

 roots of a special leguminous plant, form nodules. They 

 multiply, and their descendants have been so influenced by 

 the host plant that, liaving ceased to be neutral like the 

 original parent forms, they effect their full strength only on 

 the same leguminous species, and lose their power to set 

 up infection in any other. Here will be found the 

 explanation of strange LeguminosiT; forming nodules on 

 their roots, which nodules go on increasing from year to 

 year in number and efficacy. Leguminous plants then 

 will only, with certainty, show nodule formation if the soil 

 contain either the germs accustomed to the planted species 

 or else neutral germs. 



I would now call your attention to some experiments 

 relating to Question 2 : — 



r. AN EXPEIilMENT WITH PEA (Pisum satlvvm). 



In this experiment 6 pots were taken and filled with a 

 mixture of 4 parts quartz sand and 1 part garden earth, 

 the whole being sterilised, i.e. all germ life was killed by 

 heating. In each pot 5 pea plants were sown in the 

 beginning of June. 



Pot 1 was iiKiculatfd with pure cultures of riiasoolus bacteria. 

 ,, 2 ,, ,, Pea ,, 



,,3 ,, ,, Clover ,, 



,, 4 ,, ,, lloliiiiia ,, 



)) 5 ,, ,, JjUjiiu ,, 



,, fj was left uiiinoeuLiteil. 



At first all the pots showed an equally good growth, but 

 as time went on and the soluble nitrogen of the soil had 

 been largely consumed, the effects of inoculation began to 

 show themselves. Tlie ])lants in the pot inoculated with 

 pea bacteria, and, later, those in the pot inoculated witli 

 phaseolus bacteria were seen to be green, and were richly 



