An extensive summary of publications reporting radial specific gravity (SG) variation for North American conifers is presented. SG varies from pith to bark in 3 patterns before reaching asymptomatic values: Type 1 (SG increases with cambial age), Type 2 (SG is initially high at the pith, then decreases with age before increasing) and Type 3 (SG decreases with cambial age). North American Pinaceae have either a Type 1 or 2 pattern (majority are Type 2). North American Cupressaceae have a Type 3 pattern, but radial SG data does not exist for some species. We reviewed publications in Table 7-1 of Panshin and de Zeeuw (1970) which reports SG variation by species and Type (the 1980 edition has an equivalent table but doesn’t reference publications), examining sampling strategies and radial patterns. For a small number Type was either incorrectly interpreted or sampling made a conclusion regarding pattern of radial variation impossible. Specific examples of mislabeled Types reported by Panshin and de Zeeuw for Douglas-fir, lodgepole, red and shortleaf pine, and western redcedar are described. We conclude within an individual species the pattern of radial SG variation is consistent, however different patterns have been reported for subspecies of Douglas-fir and ponderosa pine.