Abstract
More than 95% of container-grown longleaf pine (Pinus palustris P. Mill.) seedlings had roots growing downward vertically (geotropically) when examined 7 to 8 mo after transplanting into sand. Geotropic roots were rarely the original taproot (< 0.5%) but were usually adventitious lateral roots that had formed about the callus tissue. Air-pruning in the nursery results in callus formation at the end of the taproot and typically, 1 or more adventitious roots emerge just above the callus tip. Although many first-order lateral roots were deflected downward by container walls, few exhibited positive geotropic growth after transplanting. Most grew in directions other than straight down. In this study, about 4% of the seedlings lacked geotropic roots. Longleaf pines with a long taproot or sinker roots are less susceptible to toppling at a young age than are trees without vertical roots.
