cross section through petiole (x-xylem, d-phloem)
This shows a closer view of the xylem and phloem inside the petiole. Notice that the xylem vessels have a very thick secondary wall. This offers the vessel the support it needs to withstand the tension created as the water is drawn up from the roots.

cross section through petiole (x-xylem, d-phloem)
This cross section shows us an even closer view of the vascular tissue inside petioles.

longitudinal section through petiole (vb-vascular bundle, c-collenchyma, p-parenchyma, arrows indicate trichomes)
This is a longitudinal section of the leaf petiole. Note how the vascular bundles are visible on both sides of the petiole. This is because they are distributed in a semi cylinder. We are seeing one plane of that cylinder.

cross section through petiole (x-secondary xylem, ph-secondary phloem, vc-vascular cambium, p-parenchyma)
This petiole is undergoing secondary growth. Notice that the xylem is no longer in distinct bundles but a continuous semi cylindar.

Introduction | Flowers&Fruit | Roots | Stems | Leaves

© Thomas L. Rost 1996
Section of Plant Biology Division of Biological Sciences