Division of labour
To transport water and nutrients from the soil, the xylem in broadleaf trees contains vessel elements. A vessel element, about half a millimetre in diameter, is two to twenty times larger than a tracheid, and can hold 25 to 2,500 of them!
In conifers, the tracheids, which account for most of the wood, give the tree rigidity and form most of the xylem. The vessel elements in broadleaf trees, on the other hand, account for only about 30% of the volume of the wood on average. The remainder, 20% rays and 50% tracheids and fibres, gives a broadleaf tree the rigidity its trunk needs
