ASPECTS OF AN OLD AGRICULTURAL QUESTION. 259 



turned chiefly on the following points : (1) The specific 

 nature of the living organism, called " bacteroids," in the 

 cells ; (2) their exact relation to the leguminous plant, and 

 what becomes of them when the plant dies ; and (3) their 

 behaviour outside the plant, since it was evident from 

 various observations as well as from the infection via the 

 root-hairs, that they pass some time in the soil around. 



The outcome was, put shortly, the organism having 

 invaded the root, stimulates the cells deep down in the 

 cortical tissues to divide and form a delicate tissue of hyper- 

 trophied cells ; as these enlarged cells multiply the organism 

 keeps pace with them, sending branches into each new cell. 

 Eventually myriads of bacterium-like minute bodies, so 

 generally taken to be true bacteria, but with peculiarities 

 of their own which weaken the assumption, are detached 

 from the invading branches, and fill these living cells. The 

 latter are not killed by the infecting bacteroids, but, on the 

 contrary, show signs of intense physiological activity, accom- 

 panied by the destruction of copious supplies of carbo- 

 hydrates, brought to them from the leguminous plant. 



After a time, however, the activity ceases, and the 

 myriads of bacteroids are found to be in part dis- 

 organised. Then the now vigorous leguminous plant is 

 observed to absorb the disintegrated contents of the in- 

 terior of the nodules, including the disorganised bacteroids 

 in part, the rest of the nodule, and a certain proportion of 

 bacteroids which have escaped destruction, being left as 

 ddbris in the soil. There can be little doubt that we have 

 three periods to distinguish here. First, the invading 

 organism is acting as a parasite, but though it lives at the 

 expense of the cells which it has enslaved, and forced to 

 greater and greater physiological activity, it does not destroy 

 them. In the second stage we have a period during which 

 the struggle for existence is evidently extremely intense ; at 

 first the invading organism takes everything the cells can give 

 it, but gradually it passes into a more passive condition, and 

 fills the cells with bacteroids, and all proceeds to a state 

 of comparative rest. Now begins the third stage. The 

 more and more vigorous leguminous plant exerts a draught 



