Most plants go through a process of physiological aging where a plant progresses through a juvenile, transition and mature phase.
The juvenile phase is defined as a physiological age where the plant can not flower even though the environmental conditions are suitable for flower induction.
English ivy (Hedera helix)
English ivy (Hedera helix) dramatically shows this phase change by having a different leaf shape and growth habit in the juvenile and mature phase.
Plants in the juvenile phase tend to produce cuttings that are easier to root from cuttings.
Numerous trees species show dramatic morphological changes between juvenile and mature phases of growth.
The image to the right shows the abrupt morphological changes in toothed lancewood, a New Zealand native.
The juvenile phase (white arrow) is non-branched and the leaves hang downward. The mature phase (black arrow) shows branched growth with smaller leaves no longer point down and lack the toothed leaf margin.
Toothed lancewood (Pseudopanax ferrox)
One of the important implications of phase change is the difference in the ability for cuttings to root from the juvenile versus the mature phase in woody plants.
In general, cuttings root most easily from juvenile phase cuttings. For more information on this aspect of phase change see the section on hedging.
The juvenile to mature gradient in seedling trees represent a "cone of juvenility".
The physiologically mature section of the tree is at the shoot tips, while the most juvenile section is at the root-shoot junction.
This seems odd because the chronologically oldest section of the tree behaves as the most juvenile.
Shoots (especially adventitious shoots) that arise from juvenile parts of the tree retain their juvenile characteristics and can be rooted more easily from cuttings than shoots taken from mature parts of the tree.
Juvenile shoots can be induced from stump sprouts, hedged limbs, or root suckers.
Another source of juvenile shoots are pre-existing buds under the bark that give rise to epicormic shoots or from specialized areas of the trunk called spheroblasts.
This is important to propagation because juvenile shoots root easier and perform better in tissue culture.
Leaf retention in the fall is a juvenile character and the maple tree on the right nicely illustrates the cone of juvenility.