Changes in guard cell shape and stomatal opening and closing (surface view). Guard cells of a typical angiosperm are illustrated in their turgid (stoma open) and flaccid (stoma The orientation of cellulose microfibrils in the cell walls causes the guard cells to more in length than width when turgor Since the two guard cells are tightly joined at their tips, they bow outward when turgid, causing the stomatai pore to open.