Above and below oak leaf greens
oil on canvas, 300mm x 300mm

Private collection

The two sides of oak leaves are different colours: a waxy cuticle seals the 
top, which is darker, to prevent uncontrolled loss of water by evaporation;
the underside has open pores (stomata) that control water loss and carbon
dioxide change. That is why oak trees appear to change colour in the wind.