TY - JOUR AU - Valentine, Raymond C. TI - ‘Nif’ and ‘hup’ genes JF - California Agriculture JO - Calif Agr Y1 - 1982/08/01 VL - 36 IS - 8 SP - 10 EP - 10 PB - University of California Agriculture and Nature Resources SN - 0008-0845 UR - http://www.ucanr.edu/sites/calagjournal/archive/?article=ca.v036n08p10a AB - Not available – first paragraph follows:All crops need nitrogen for growth. Nitrogen fixation—the enzymatic conversion of atmospheric nitrogen gas into a form available to the plant—is a trait that only some bacteria have evolved.