 This is not the case in tree forks, as each branch is roughly equal in size and no substantial tissues from either branch is embedded into the other, so there is no reinforcing knot to supply the mechanical strength to the junction that will be needed to hold the branches aloft.Research has shown that a unique wood grain pattern at the apex of forks in hazel trees ("Corylus avellana" L.) acts to hold together the branches in this species, and this is probably the case in most other woody plants and trees.This is an example of 'trade-off' in xylem, where mechanical strength to the tree's junction is gained at the expense of efficiency in tree sap conductance by the production of this specialised wood, known as 'axillary wood'.