1. Akkermans, A.D.L. 1971. Nitrogen fixation and nodulation of Alnusand Hippophaëunder natural conditions. Ph.D. Thesis, Univ. Leiden, The Netherlands, 85 pp.
2. Akkermans, A.D.L., van Straten, J. and Roelofsen, W. 1977 Nitrogenase activity of nodule homogenates of Alnus glutinosa: A comparison with the Rhizobium—peasystem. In: Recent Developments in Nitrogen Fixation, pp. 591–603. Newton, N., Postgate, J.R. and Rodriguez-Barrueco, C., (eds.), Proceedings 2nd International Symposium on Nitrogen Fixation, Salamanca, 1976, Academic Press, London.
3. Akkermans, A.D.L., Abdulkadir, S. and Trinick, M.J. 1978 N2-fixing root nodules in Ulmaceae: Parasponiaor (and) Tremaspp.? Plant and Soil 49, 711–715.
4. Akkermans, A.D.L., Abdulkadir, S. and Trinick, M.J. 1978 Nitrogen fixing root nodules in Ulmaceaea. Nature, London, 274, 190.
5. Allen, M.B. and Arnon, D.I. 1955 Studies on nitrogen-fixing blue-green algae I. Growth and nitrogen fixation by Anabaena cylindricaLemm. Pl. Physiol. 30, 366–372.