A Comparison of Root- and Shoot-wood Development in Conifer Seedlings

Tracheid diameter, wall thickness, and wall area per tracheidincreased towards the root tip in first-year seedlings of Piceasitchensis and Pinus sylvestris; this is shown to be associatedwith differences in duration of the expansion and wall thickeningphases of tracheid development. Transfer to short days producesa similar response throughout the plant, tracheid diameter andwall thickness decreasing shortly after transfer, due to a declinein rate of development. These data are discussed in relationto growth-regulator gradients likely to exist between root andshoot. It is pointed out that though effects of growth regulatorson tracheid dimensions are well documented, it has yet to beestablished whether this is due to their regulation of the rateor of the duration of development.