BY K. GREIG-SMITH. 615 



Having been able to prove that the compound bacterium can gain 

 nitrogen from the atmosphere and knowing that the slime is 

 nitrogenous, we can see the method by which the plant is 

 nourished by the bacterium. And still the conclusion which 

 was arrived at in my research upon the slime holds good. The 

 slime is a cell or plant nutrient, but in addition to the gum con- 

 stituent being peculiarly suited for building up the carbohydrate 

 of the nucleoproteid molecule, as I have pointed out, it has also an 

 albuminous constituent which is capable of making the plant 

 independent of the supply of soil nitrogen in certain circum- 

 stances, e.g., in nitrogen-free soils. We are now certain of the 

 kind of help which the bacterium gives the plant. There exists 

 a symbiosis; the plant supplies saline and saccharine matter, the 

 latter of which the bacterium converts into gum and at the same 

 time elaborates atmospheric nitrogen into constituents which are 

 partly contained within the bacterial cell and partly diffused in 

 the gum, which by virtue of their presence appears as a slime. 

 Both the nitrogenous and the carbohydrate constituents of the 

 slime are then elaborated by the plant cells into tissue elements. 



