From the Editors. 223

Adams, M.W. Plant architecture and yield breeding. 225

Heichel, G.H. Breeding alfalfa for improved nitrogen fixation: A physiological perspective, 255

Loomis, R.S. McDermitt's method for relating elemental composition of plant materials to respiration and yield. 281

McCree, J.J. The role of respiration in crop production. 291

Shannon, J.C. A search for rate-limiting enzymes that control crop production. 307