My thanks to Guy Bussières at Université Laval, in Québec City for directing me to a 2012 paper by Colin et al. (Annals of Botany 110: 995-1005) which describes these bumps as a form of epicormic growth they called spheroblasts, "Isolated buds progressively engulfed in a small ball of wood generated from the base of the bud on the external side". John A. McLaughlin, PhD Forest Research Pathologist Ontario Forest Research Institute 1235 Queen St. E. Sault Ste. Marie, ON Canada P6A 2E5 tel: +1 705-946-7419 cell: 705-542-2851 John.McLaughlin@ontario.ca<mailto:John.McLaughlin@ontario.ca> http://ontario.ca/ofri