“…Oak, on the other hand, used by Usoskin et al [2013] and Rakowski et al [2015], is a ring-porous angiosperm (also called hardwood or deciduous tree) [Ladefoged, 1952;Speer, 2010]. Studies of modern Δ 14 C values in earlywood and latewood fractions from gymnosperms, in particular, cedar [Yamada et al, 2008;Rakowski et al, 2010] and pine trees [Sheng et al, 2016], suggest that both fractions are consistent with the average atmospheric Δ 14 C value of the warm summer months (May-September) during the year of formation. The cell types forming gymnosperms are generally simpler than the cell types in angiosperms.…”