Maidenhair tree (Ginkgo biloba) petiole. Light micrograph of a section through a leaf from a maidenhair tree (Ginkgo biloba), showing the upper and lower epidermis (both blue) and stomata (pores). Beneath this is the palisade mesophyll tissue (brown), containing chloroplasts and air spaces. Then there is the spongy mesophyll (brown) of parenchyma cells and chloroplasts. The mid-rib (vein) contains the vascular bundle composed of a ring of endodermis (white) with metaxylem of thick-walled tracheid cells (red) and protoxylem (also red) of thin-walled cells. Beneath the xylem is the phloem, consisting of sieve tube cells (blue). Magnification: x37 when printed 10 centimetres wide.