Development of white spruce (Picea glauca) seedling roots

Abstract

The root system of container-grown white spruce seedlings (Picea glauca (Moench) Voss) consists of a taproot and many lateral roots. The lateral roots can be divided into three classes on the basis of external morphology. Although growth cycles of individual roots are independent, there are overall trends of growth in the root system. A preponderance of one morphological root class is usually associated with a specific phase of the growth cycle. Apical organization in absorbing and elongating roots is similar. When elongation ceases, roots become brown as a result of two separate processes, suberization of the endodermis and metacutization of a discrete layer enveloping the root apex. Zonation in the apex is reduced in brown roots. Renewed growth is marked by swelling of the brown root apex followed by the emergence of a white root tip.