Fig. 10.4-1. Transverse section of milkweed petal (Asclepias tuberosa). Compare the upper and lower epidermises of this petal – the epidermis cells on the lower side have a rather ordinary shape, but those on the upper side each bulge outward as a large papilla. You can see that the papilla is formed as the outer wall and the protoplast bulge outward; this same surface texture could also be created by having a round protoplast with a thickened wall or an ordinary protoplast and wall with a thickened cuticle. Papillose epidermis cells are quite common on petals, giving them a velvety appearance.