MANUAL FOR SUGAR GROWERS. 29 



many of the cells of which contain starch ; distrib- 

 uted throughout the central mass of tissue are a 

 number of what the author distinguishes as " special 

 cells" (b) ; these are usually rather large in size and 

 do not contain starch, but are rilled with countless 

 bacteria or microbes. Not very much is known re- 

 specting these root-nodules, 

 the active agents in which 

 appear to be the bacteria or 

 microbes ; for the nodules do 

 not form on the roots of 

 plants grown in sterilised 

 soil, that is, in soil subjected 

 to such treatment, before the 

 seeds are planted, as will de- F '' 

 stroy vegetable life, and that 

 they will form if a little unsterilised soil be af- 

 terwards added to the sterilised. It has been as- 

 sumed (for very little has been proved so far) that 

 these bacteria, which appear to exist in all fer- 

 tile soils, have the power of forming colonies on 

 the roots of certain plants, and that so situated 

 they have the power of assimilating atmospheric 

 nitrogen ; and that after its assimilation by the bac- 

 teria the nitrogen becomes available for the food- 

 supply of the host on which the nodules are found. 

 It has even been suggested that these bacteria are 

 capable of assimilating atmospheric nitrogen without 

 being associated with another plant. The increase 

 of nitrogen in a leguminous crop renders these 

 plants very valuable for the purpose of green dress- 

 ing, as this will result in a gain of nitrogen to the 



