654 



THE NODULE ORGANISM OF THE LEGUMINOS^, 



gain of nitrogen, while with the survival over this sick period the 

 nodules appeared, and there was a considerable gain of nitrogen. 

 From this the inference was naturally drawn that leguminous 

 plants could gain their nitrogenous food by absorbing the atmos- 

 pheric nitrogen in some way, and that this action had an intimate 

 relation with the nodules formed upon the i-oots. In other words, 

 the nodules were capal^le of elaborating gaseous nitrogen into 

 nitrogenous forms capable of being assimilated by the plant. 



Hellriegal and Wilfarth in this way indirectly proved the 

 fixation of nitrogen by showing that the matui'e plant contained 

 more nitrogen than was originally in the soil. Schloesing and 

 Laurent afterwards proved the fact directly by a loss of the 

 atmospheric nitrogen in contact with the plant. Woronin, 

 Marshall Ward and Frank had shown that the nodules did not 

 form on the roots when the plants were grown in either sterilised 

 soil or water, and it was only when the sterile soil was infected 

 with ordinary soil, or when the plants in water culture had pieces 

 of chopped nodules inserted between the root hairs, that nodules 

 were produced. Woronin, as early as 1866, had suggested the 

 presence of bacteria in the nodulai- tissue, and the earlier experi- 

 ments Ijore out the idea. 



Marshall Ward was the first to describe the entry of the 

 organisms into the tissues of the plant through the root hairs. 

 A bright spot was observed on the outer epidermal cell wall of 

 the root hair: this fused with the cell wall, and emerging on the 

 inner side, grew along the inside of the hair as a filament which 

 reached the deeper layers of the cortex cells, and these by their 

 proliferation ultimately formed the nodule. Since infection only 

 occurs on the root hair the location of the nodule is accidental. 

 The interior of the nodule is occupied by al])uminoid cells, where 

 the cellulose-dissolving infecting thread can be seen branching 

 and passing like a mycelium from the protoplasm of one cell 

 thiough the cell wall into the protoplasm of a neighbouring cell. 

 The method of entry of the organism was confirmed by Prazmowski, 

 who further saw a number of rods inside the simple filament of 



