Symbiotic Nitrogen Fixation in Non-leguminous Plants. III. Experiments on the Growth in Vitro of the Endophyte of Alnus glutinosa

1. A method is described that enables the determination of the amount of endophyte in a suspension of root nodules or an inoculated nutrient solution in a semi-quantitative way. 2. This method is used for the study of the development of the endophyte in several nutrient solutions. 3. The usual nutrient solutions do not enable any development of the endophyte. The development is not promoted by the addition of the well known growth substances, amino acids and nucleic acid components. 4. While most soil- and peat suspensions do not enable the development of the endophyte, in some peat suspensions a definite development was measured. 5. The difference between the usable and the unusable peat suspensions is caused by the presence of growth-inhibiting substances in the unusable peat. 6. Alcoholic extracts of the usable peat, prepared after a previous water extraction, contain a growth-promoting factor that enables the growth of the endophyte on the usual nutrient solution. 7. The endophyte does not grow in suspensions of alder roots. 8. Alcoholic extracts of nitrogen-poor alder roots, prepared after a thorough water extraction sometimes contain the growth-promoting subst g ces, while other extracts contain growth-inhibiting substances.