As we move toward later (cooler) types along the main sequence after A5, the hydrogen lines now begin to weaken, as the hydrogen lines reach their maximum strength in the early A-type stars. In addition, the Ca II K-line continues to strengthen, although it becomes essentially saturated by the late F-type stars. The general strength of the metallic-line spectrum (note especially the features marked on the illustration) grows dramatically. Around F2, depending upon the resolution of the spectrum, the G-band makes its first appearance. The G-band is a molecular band, composed of thousands of closely spaced lines due to the diatomic molecule CH.