On the Anatomy of the Roots of Apple Seedlings

Abstract

1. Differentiation in the apple root proceeds in an acropetal direction. Although vacuolation occurs in the metaxylem region first, this tissue is the last to mature. Sieve tubes are the first vascular elements to mature, followed by xylem. 2. Thickenings occur on the radial and transverse walls of the cortical cells just outside the endodermis. These thickenings develop simultaneously with the first protoxylem elements. The phloroglucin-hydrochloric acid test indicated that they become lignified at the same time and to the same degree as the protoxylem elements. 3. The layer of cells immediately outside the primary vascular tissue was designated as pericycle, and the next layer of cells as endodermis. 4. Suberin lamellas develop on the walls of the cells of the endodermis. The deposition takes place at first in the cells outside the primary phloem poles and then proceeds toward the primary xylem poles. 5. The number of xylem arcs which develop is not constant but appears to be correlated with the diamete...