LEAVES ARE THE MAIN SITES OF PHOTOSYNTHESIS and transpiration (water loss &nbs p; by evaporation ) in plants A typical leaf consist of a thin , flat lamina (blade) supported by a network of veins , a petiole(leaf stalk); and a leaf base ,where the petiole join the stem . Leaves can be classified as simple , in which the lamina is a single unit , or compound , in leaflets.Compound leaves may be pinnate , with pinnae (leaflets) on both sides of a rachis (main axis ),or...