Sites of first phellogen initiation in conifers

Abstract

Sites of first phellogen initiation were studied in ten species of Pinaceae and Cupressaceae. The distance from the apex, age and the tissue from which the first phellogen is initiated, were determined. In Pinaceae the first phellogen arises at a shorter distance from the apex than in Cupressaceae. In fast-growing leaders, or seedlings, suberization appears at a larger distance from the apex as compared to slow growing branches. Differences between Pinaceae and Cupressaceae are probably related to differences in the contribution of leaf-bearing organs and branches to photosynthesis. These differences represent a compromise between protection by suberisation in Pinaceae and increase in the photosynthetic area in Cupressaceae.