The Leaves of Juvenility

Why do autumn leaves stay up there in the trees sometimes until spring?  Ah, yes, there they are.  The Leaves of Juvenility.  Some species of plants are interesting this way.  Some plants start out from seed as a physiologic juvenile. That is they cannot sexually reproduce until they are older.  They are similar to animals who go through puberty before they can sexually reproduce.  (Exceptions to this are called neonates but we will pretend they are the freaks that they are).  But plants are funny creatures.  As a seed sprouts, it lays down a history of growth.  The first part of the stem and the branches are produced when they are young and forever retain the  characteristics of juvenility.  They get bigger around and all, just juvenile.  (Definition of juvenile is not able to sexually reproduce.)  When the plant has grown some and has gone through a certain  number of cell divisions, the growing point decides that it is now time to sexually reproduce.  It now makes plant stems that, when given the correct cues, may flower and reproduce.  Most plants are not visually clear when they do this.  But some species have differently shaped leaves, or color or other characteristics that are only present in the mature parts of the plants.  One of the characteristics is the ability to make an abscission layer and shed their autumn leaves in the fall.  When you see a tree with a bunch of retained dead brown leaves in the center of the tree, you know something.  It probably grew from a seed and the base of the tree is of juvenile origin.  The tree made branches and stuff but only the tips of branches were of sufficient age to become mature tissue. 

The trees that I can think of that do this are few.  The oak and beech do this but not too many others.  Ivy and maples have a different leaf shape when they are juvenile and change shape when they are old enough to flower and fruit.  A more inclusive list should be drawn up. Someone should do that.

Tags:Autumn leaves,trees

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