If there was gradually increasing light center of the tree trunk (as if it were a tunnel out), it would lead back to the Kokiri Forest, but if it was a flat wall of blackness, it would continue through the woods. (zelda.gamepedia.com)
At the center of the tree - filled atrium, an opulent chandelier dangles over a grandiose fountain, as luxurious a setting for a bacon club sandwich as there ever was. (bonappetit.com)
In timber production, the older, darker heartwood in the center of the tree trunk is particularly valuable, and it was this wood that was investigated in the study. (sciencedaily.com)