ON THE ABSCISSION REGION IN LEAVES OF THE BLUE SPRUCE

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Abstract
The problem of leaf fall due to desiccation was re-examined in Picea. It was found that abscission took place with equal facility regardless of which side of the abscission zone was subjected to more rapid desiccation; that prior to a certain stage of development the leaves failed to fall when dried; and that, for some time after this, they fell more rapidly than after reaching maturity. Microchemical study indicated that a change from pectic acid to soluble pectin in the abscission layer coincided in time with the earliest stage at which fall would be produced by desiccation, and that the decreasing ease of abscission for some time after this corresponded with the increase in amount and lignification of the secondary vascular tissue. It was concluded that the changes leading to abscission here are identical with those in deciduous forms and that the leaves are retained on the branches because of their strong vascular bundles, which become brittle on drying.

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