This woody central part of a tree trunk consists of sapwood & heartwood
Similar to the veins in 
animals, veins in leaves and tree trunks transport fluid and minerals ... heartwood
: The older, non-living central wood of a tree or woody plant, usually darker and... [DOC] [TLE] Wood - Wikipedia [PAR] Wood is a porous and fibrous structural tissue found in the stems and roots of 
trees, and other woody plants.