122 JOURNAL OF THE 



exclusion of all other organisms, could provide the necessary 

 nutriment from the store of nitrogen in the atmosphere. But 

 whether from nitrogen in combination, or, as Hellriegel (/. c.) 

 claims, from the elementary nitrogen of the atmosphere, the 

 researches have not yet been carried far enough to say. 



If bacteria taken out of the knots in peas are cultivated in 

 suitable nutrient media they increase for an unlimited time by 

 fission, retaining a rod-like form. In the knots under the influ- 

 ence of the plant they increase in the same way and possess the 

 same form until the time when dissolution of the membrane of 

 the bacteria-tube takes place and they are set free in the bacteroid 

 tissue. In the plasmic contents of the cells of the bat^teroid tis- 

 sue they increase for a time, but change their form and branch in 

 a forked manner forming X and Y forms. At last tlieir bodies 

 become hyaline and dissolution takes place. The plant begins 

 to empty the older cells of the bacteroid tissue by appropriation 

 of their contents for its own use. The time when this absorp- 

 tion of the contents of the bacteroid tissue begins and the energy 

 with which it proceeds bears a distinct relation to the amount of 

 nitrogenous matter in the soil at the command of the plant. 

 When the soil is well supplied with it the knots grow to consid- 

 erable size, the bacteroid tissue is filled with bacteria and bacte- 

 ria-tubes and presents a flesh-red color, and remains in this con- 

 dition until the maturity of the plant. The dissolution of the 

 bacteroids and the emptying of the bacteroid tissue proceeds very 

 slowly and irregularly. On the other hand, when there is a 

 scarcity of nitrogenous matter in the soil at the command of the 

 plant the dissolution of the bacteroids and the emptying of the 

 bacteroid tissue begins early and proceeds rapidly while the bacte- 

 roid tissue has a greenish color. 



In both cases the emptying begins in the oldest part of the 

 bacteroid tissue and advances towards the meristematic zone. 

 Even in the oldest part of the bacteroid tissue remain numerous 

 living bacteria and tubes containing bacteria, which, with those 

 in the peiipheral zone of tiie parenchymatous tissue escape into 

 the ground upon the decay of the knot and tiiere increase and 

 perpetuate the infectious character of the soil. 



