Spectroscopic observations are reported for 23 population II subdwarfs (selected for age homogeneity) and 31 other stars (mainly population I F and G dwarfs). The spectra were obtained in the 670.7-nm line of Li I using coude spectrographs on the 2.7-m reflector at McDonald Observatory, the 3.0-m reflector at Lick Observatory, and the 4-m Mayall reflector at KPNO during 1983-1985. The results are presented (along with selected published data) in extensive tables and graphs and analyzed. For 12 stars with space velocities v(LSR) = 160 km/s or greater and Fe/H = -1.4 or less, the atmospheric Li/H abundance is shown to depend on T(e), the mean value for T(e) = 5600 K or more being Li/H = (1.2 + or - 0.3) x 10 to the -10th. This result, also found for many of the population I stars, is interpreted as a significant constraint on the cosmic baryon/photon ratio.