The first leaves to appear when the seed germinates are often the seed leaves or cotyledons ). There can be only one (in MONOCOTS), two (in DICOTS) or many cotyledons (in conifers).
Jewel weed (a dicot)	Spiderwort (a monocot)
Vascular tissue from the stem continues through the petiole into the veins of leaves. Leaves have a waxy protective layer on the outer surface of their cells called the cuticle (Q-tick-uhl). This protective layer reduces the loss of water (DEHYDRATION) and helps prevent disease-causing organisms from entering. Sometimes the cuticle makes it difficult for herbicides to stick to and enter the leaf.
Section of lilac leaf

New seedlings and houseplants should be gradually moved into sunlight. This allows the layer of cutin to build up gradually and protect tender plants from SUNSCALD. Sunscald is the result of too much water being lost from heat and wind.