ANNUAL RING FORMATION IN PINUS PALUSTRIS SEEDLINGS

Abstract

Longleaf pine (Pinus palustris Miller) in its seedling stage differs markedly from all the other pines indigenous to the Southern States. When the longleaf pine seed falls on the ground during October and November, it does not lie dormant until the following spring as do the seeds of the other pines, but in two or three weeks, if weather conditions are favorable, the seed germinates. Three definite stages in the development of the seedling can be observed. The first stage is characterized by the presence of the cotyledonary or seed leaves, which function for only a few months. These are succeeded by the primary leaves, which arise on the main axis, and after several months may disappear or be transformed into permanent scales. This second stage usually terminates at the beginning of the second spring; when secondary or foliage leaves appear in the axils of the primary leaves. The third stage then follows, in which the foliage leaves are fully developed and are morphologically distinct from the primary leaves. At this time the main axis of the stem is hidden by the central tuft of the foliage leaves. The growth of the stem is very slow and hardly noticeable. In this condition the seedling may remain for several years, showing very little increment in height or diameter. In the other southern species of pine the seedlings begin height growth soon after germination; such a stand of seedlings, now I2 years old, is under observation in southern Louisiana. The roots of the longleaf seedlings, however, grow rapidly, resulting at the end of 3 or 4 years in a well developed root system. Seedlings in this stage-that is, when the needles arise from a central cushion-like region and not directly from a terminal, well developed bud-are said to be in the grass stage, for at this time they are practically indistinguishable from the surrounding grasses. Only an experienced eye can detect a longleaf pine seedling in a stand of green grass. During the grass stage there appears to be no marked active and dormant season in the growth of longleaf seedlings. Even during the winter months if weather conditions are favorable, new needles are often seen arising from the central cushion-like region. After several years, depending on individual seedlings and on site conditions, the main axis, which up to that time has been hidden by the central tuft of needles, begins to rise and ultimately forms a pointed bud. When this becomes the characteristic fuzzy, silvery longleaf pine bud, the third stage is 599