plants-buds-twigs-3

plants-buds-twigs-3 - 3 Leaf fall axillary bud Leaf fall,...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
Leaf fall, or abscission (Fig. 4) Most trees shed their leaves. Deciduous trees do so in the autumn, while evergreens may shed theirs at intervals throughout the year. In certain trees, abscission takes place as follows: cells at the base of the leaf-stalk divide and form layers of cells across the region where the petiole joins the stem. The inner layers of this new tissue become corky and the vessels become blocked so that the leaf is deprived of water. Before this occurs, the contents of the cell begin to break down chemically, producing the characteristic red and yellow autumnal tints. The cells' contents are digested and the soluble products absorbed back into the tree. The cells beyond the corky layer degenerate, and the dried-up leaf falls, leaving a scar on the stem protected from the entry of bacteria and fungi by impermeable cork. The details of abscission vary in different species. axillary
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/29/2011 for the course BIO 218 taught by Professor Young during the Fall '11 term at BYU.

Ask a homework question - tutors are online