The 407-year-old pear tree in Gansu can still bear fruit after being burned out. Why?

Let's first understand the structure of trees, especially the part of nutrient and water transportation. Firstly, two basic concepts, phloem and xylem, are introduced.

Phloem transports nutrients in ferns and seed plants, and also has the function of support and storage. The phloem consists of sieve tubes and companion cells, phloem fibers and phloem parenchyma cells. The sieve tube is the basic component of phloem, and its main function is to transport nutrients such as sugar, protein and some mineral ions. The sieve tube is very obvious under the microscope, while the bast fiber is tough and has strong bending resistance, which plays a mechanical support role in the phloem.

Phloem is divided into primary phloem and lifelong phloem. For plants like pear trees, the primary phloem will be squeezed in the growth process of various parts of the plant, and then quickly lose its function and be completely destroyed, while the secondary phloem constitutes most of the bark, so this can explain why hollow pear trees can still survive, because the bark contains secondary phloem to transport nutrients and promote the maintenance of basic life activities of pear trees.

Xylem is also the transport organization of vascular plants, which is responsible for transporting water absorbed by roots and inorganic ions dissolved in water upward for other organs and tissues in plants, and also has the function of supporting plants. Xylem is composed of vessels, tracheids, wood fibers, xylem parenchyma cells and wood rays. Secondary xylem is located between primary xylem and primary phloem, such as annual rings. The secondary xylem produced by vascular cambium in a growing period constitutes a growth ring. In xylem, vessels and tracheids are mainly responsible for transporting water.

Phloem for transporting nutrients and xylem for transporting water form vascular system in various organs of plants.

Hollow pear trees can blossom and bear fruit without these two parts. This pear tree is over 400 years old, so it is very enlightening to think about it.