The images show the prepairation of the cleavage of tissue at the base of the petiole. During the perspiration, ions, which are introduced via the roots, constantly remain behind in the leave tissue, which accumulate over time to such an extent, that they slow down the photosynthesis.
In addition, the water supply in freezing weather becomes so difficult, that the perspiration has to be greatly reduced. Therefore, our deciduous trees shed their leaves in autumn or sooner, also depending on the amount of accumulated ions. This is an active, hormonally controlled process, which takes place in a separating layer consisting of multiple layers of parenchyma cells, at the base of the petiole. There, several enzymes dissolve either the middle lamellae alone, or together with the primary walls or the entire cells. Then the vascular bundles tear off, and the leaf can drop. As the images show, the point of attachment of the petiole is protected from dehydration and infection, by a layer of cork, which has already been laid out before the leaf falls.
Premature defoliation at the base of the leafstalk or petiole. Damage from road salt (ions).
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