It is, in fact, fully established that these leguminous crops acquire a considerable amount of nitrogen by the fixation of the free nitrogen of the atmosphere under the influence of the symbiotic growth of their root-nodule-microbes and the higher plant.
Eitel, knot, nodule, cf.
The heaviest nodule weighed over 20 tons.
In 1897 Peary brought the largest nodule to New York; it was estimated to weigh nearly loo tons.
The bacteria, which are present in almost all soils, enter the root-hairs of their host plants and ultimately stimulate the production of an excrescent nodule, in which they live.
Later the nitrogen-content of the nodule decreases, most of the organisms, which are largely composed of proteid material, becoming digested and transformed into soluble nitrogenous compounds which are conducted to the developing roots and seeds.
The nitrogen-fixing nodule bacteria can be cultivated on artificial media, and many attempts have been made to utilize them for practical purposes.
At the base of the Red Crag in East Anglia, and occasionally at the base of the other Pliocene Crags, there is a " nodule bed," consisting of phosphatic nodules, with rolled teeth and bones, which were formerly worked as " coprolites " for the preparation of artificial manure.
The "eagle stones" of older writers were generally concretions of this kind, containing some substance, like sand, which rattled when the hollow nodule was shaken.
A, root nodule of the lupin, nat.
Thus, to mention examples, diphtheria toxin produces inflammatory oedema which may be followed by necrosis; dead tubercle bacilli give rise to a tubercle-like nodule, &c. Furthermore, a bacillus may give rise to more than one toxic body, either as stages in one process of change or as distinct products.
In the cells of the nodule the bacteria multiply and develop, drawing material from their host.