| Abstract: | A quantitative study of the fixation of nitrogen and of itstransfer from the nodules to the remainder of the plant hasbeen made in Alnus plants during their first season of growth.Fixation per plant reached a maximum in late August but fellrapidly with the onset of autumn, while fixation per unit dryweight of nodule tissues was greatest in young nodules and wasof the same order as in nodulated legumes. Throughout the growthseason there was a steady transfer from the nodules of some90 per cent, of the nitrogen fixed. The rate of fixation relativeto the growth of the endophyte is much higher than in free-livingnitrogen-fixing organisms and is clearly governed by the nitrogenrequirements of the entire symbiotic system. These findingsare compatible with the view that the fixation process is extracellularto the endophyte. |
