Evidence is provided that T. ambiguum, in common with other legumes, responds to inoculation with an effective strain of Rhizobium both in the field and in the glasshouse. There were consistent differences between the responses of 2x, 4x; and 6x: chromosome races to inoculation. Grass plants grown alongside effectively nodulated T. ambiguum plants gave significantly higher yields than those grown with ineffectively nodulated plants. The higher percentage germination associated with inoculation may be due to an effect of the skim milk used as inoculum carrier.
We wish to thank Professor P. T. Thomas and Mr W. Ellis Davies of the Welsh Plant Breeding Station, for their interest and advice, and Professor A. H. Bunting, of Reading University, for reading and correcting the manuscript.