Initiation of primordia in apical meristems is correlated to heightened auxin levels. The primary meristems in turn produce the two secondary meristem types. Shoot apical meristems produce one or more axillary or lateral buds at each node. Branching occurs to form new apical meristems. Secondary growth occurs at the lateral meristems, namely the vascular cambium and cork cambium. Plant inflorescence architecture depends on which meristems becomes flowers and which become shoots. Light activates photo-receptors and triggers signal cascades in plant cells of apical or lateral meristems. Root apical meristems are not readily cloned, however. Growth from apical meristems is known as primary growth, which encompasses all elongation. Proplastids are commonly found in an adult plant's apical meristems. The apical meristems start growing and give rise to the root and shoot. Plant stem cells are innately undifferentiated cells located in the meristems of plants. The apical meristems are layered where the number of layers varies according to plant type. Each seed has an embryo that is undifferentiated and lacks root and shoot meristems. Apical meristems are the completely undifferentiated (indeterminate) meristems in a plant.