Pine tree needle. Light micrograph of a transverse cross-section through a needle from a black pine (Pinus nigra) tree. This leaf is needle-like in order to reduce water loss (transpiration). The epidermis consists of thick-walled cells covered with a layer of cuticle. Below the epidermis is the mesophyll, which includes the resin canals. The central oval is the vascular cylinder, surrounded by the endodermis. Bright field illumination. Magnification: x70 when printed at 10 centimetres wide.