11. What is the outermost surface of an herbaceous stem? 12. The outer walls of this layer are encrusted with a chemical made up of fatty substance that makes the wall impermeable to water. The chemical itself has one name; the encrusted layer has its own name. a. What is the name of the substance? b. What is the name of the layer? 13. A stoma allows carbon dioxide to pass through the epidermis. a. What is the name of the two cells that control the opening and closing of a stoma? b. What is the name of the hole itself that carbon dioxide passes through? 14. Leaves carry out many roles in a plant's life. Give examples of leaves that do the following: a. Provide protection b. Provide support c. Provide storage d. Obtain nitrogen 15. If a leaf has a blade that consists of one piece of tissue, we say the leaf is a. But if the blade consists of several pieces, we say it is a b. What type of leaf found on rose? c. What type of leaf found on Virginia creeper?.